JP7545308B2 - Electronic clock - Google Patents

Description

The present invention relates to an electronic watch.

Patent document 1 discloses an electronic watch equipped with a detection circuit that determines whether or not the rotor is rotating based on the back electromotive force generated by the free vibration of the rotor. Figure 1 of patent document 1 discloses a configuration that determines whether or not the rotor is rotating by using transistors 19 and 20 connected to VDD, which is the high voltage side, and detection resistors 15 and 16 as switches.

JP 2000-75063 A

Here, in order to reduce power consumption, it is preferable to drive the step motor with low power consumption. However, when the step motor is driven with low power consumption, the free vibration of the rotor becomes small, making it difficult to detect rotation with high accuracy. In other words, there is a risk that the rotor may be determined to be not rotating even though it is rotating. Therefore, it is necessary to devise a way to increase the detection sensitivity while reducing power consumption. It is also possible to increase the detection sensitivity by using multiple operational amplifiers and regulators, but this makes the circuit configuration complicated.

The present invention was made in consideration of the above problems, and its purpose is to increase the detection sensitivity of rotation determination using a simple circuit configuration.

(1) An electronic watch comprising: a step motor including a rotor and a coil; a driver circuit for driving the step motor; a first detection resistor; a second detection resistor; a first switch connected to one terminal of the coil via the first detection resistor; and a rotation detection circuit for detecting whether the rotor has rotated based on a back electromotive current generated by free vibration of the rotor, the driver circuit being connected to at least a high reference voltage, and the first switch and the second switch being connected to a low reference voltage lower than the high reference voltage.

(2) In (1), an electronic watch has a variable power supply whose power supply voltage fluctuates and a power supply voltage detection circuit that detects the power supply voltage, and the rotation detection circuit uses the first switch and the second switch to determine whether the rotor has rotated or not when the power supply voltage is greater than a first threshold value at the time of rotation detection.

(3) In the electronic watch of (2), the first switch is an N-channel MOS transistor having a drain terminal connected to the first detection resistor and a source terminal connected to the low reference voltage, and the second switch is an N-channel MOS transistor having a drain terminal connected to the second detection resistor and a source terminal connected to the low reference voltage.

(4) In any one of (1) to (3), the rotation detection circuit includes a first determination unit connected between the first detection resistor and one end of the coil and determining whether a detection value equal to or greater than a second threshold is detected in the first detection resistor, and a second determination unit connected between the second detection resistor and the other end of the coil and determining whether a detection value equal to or greater than a third threshold is detected in the second detection resistor.

(5) In any one of (1) to (4), the circuit detection circuit further includes a third switch connected to one terminal of the coil via the first detection resistor and a fourth switch connected to the other terminal of the coil via the second detection resistor, and the third switch and the fourth switch are connected to the high reference voltage.

(6) In (5), an electronic watch has a detection sensitivity selection circuit that selects whether to use the first switch and the second switch, or the third switch and the fourth switch, or whether to use neither of them during rotation detection operation by the rotation detection circuit.

(7) In (6), an electronic watch has a variable power supply whose power supply voltage fluctuates and a power supply voltage detection circuit that detects the power supply voltage, and the detection sensitivity selection circuit selects the first switch and the second switch when the power supply voltage is greater than a fourth threshold, and selects the third switch and the fourth switch when the power supply voltage is equal to or less than a fifth threshold.

(8) In (6), the electronic watch, in which the detection sensitivity selection circuit selects the first switch and the second switch when the duty ratio of a normal drive pulse that normally moves the hands is smaller than a sixth threshold, and selects the third switch and the fourth switch when the duty ratio is equal to or greater than a seventh threshold.

(9) In any one of (5) to (8), the third switch is a P-channel MOS transistor having a drain terminal connected to the first detection resistor and a source terminal connected to the high reference voltage, and the fourth switch is a P-channel MOS transistor having a drain terminal connected to the second detection resistor and a source terminal connected to the high reference voltage. An electronic watch.

(10) In any of (1) to (9), an electronic watch has a normal drive pulse generation circuit that generates and outputs a normal drive pulse that moves the hands normally, and has a drive rank selection circuit that selects the drive rank of the normal drive pulse based on the detection result by the rotation detection circuit.

(11) In any one of (1) to (10), the high reference voltage is 0 and the low reference voltage is a negative voltage.

According to aspects (1) to (11) of the present invention, it is possible to increase the detection sensitivity of rotation determination with a simple circuit configuration.

1 is a block diagram showing an outline of the overall configuration of an electronic timepiece according to a first embodiment. FIG. 4 is a diagram showing an example of a waveform of each pulse output in the first embodiment. FIG. 2 is a circuit diagram showing a driver circuit and a rotation detection circuit according to the first embodiment. 5A and 5B are diagrams illustrating ON/OFF control of a driver circuit and a rotation detection circuit in the first embodiment. 6 is a flowchart showing rank setting control of a normal driving pulse based on a rotation detection operation in the first embodiment. FIG. 4 is a waveform diagram showing an example of a case where rotation determination is performed in the rotation detection operation of the first embodiment. FIG. 11 is a waveform diagram showing an example of a case where a non-rotation determination is made in the rotation detection operation of the first embodiment. 11 is a diagram showing an example of a waveform detected in a rotation detection operation when a conventional circuit configuration is adopted; FIG. FIG. 11 is a block diagram showing an outline of the overall configuration of an electronic timepiece according to a second embodiment. FIG. 11 is a circuit diagram showing a driver circuit and a rotation detection circuit according to a second embodiment. 10 is a flowchart showing rank setting control of a normal driving pulse based on a rotation detection operation in the second embodiment. FIG. 13 is a circuit diagram showing a driver circuit and a rotation detection circuit in a modified example of the second embodiment. FIG. 1 is a circuit diagram showing a driver circuit and a rotation detection circuit according to a conventional example.

Each embodiment of the present invention will be described in detail below with reference to the drawings.

[Overview of the electronic watch 100]
First, an overview of an electronic timepiece 100 according to a first embodiment will be described with reference to Fig. 1 and Fig. 2. Fig. 1 is a block diagram showing an overview of the overall configuration of an electronic timepiece according to a first embodiment. Fig. 2 is a diagram showing an example of the waveform of each pulse output in the first embodiment.

As shown in FIG. 1, the electronic watch 100 includes a power supply 1, a reference signal generating circuit 2, a normal drive pulse generating circuit 3, a correction drive pulse generating circuit 4, a rotation detection pulse generating circuit 5, a selector 6, a driver circuit 7, a step motor 8, a rotation detection circuit 9, and a drive rank selection circuit 10.

[Overview of the electronic watch 100: Step motor 8]
The step motor 8 is composed of a rotor RT, a coil C, and a stator ST (see FIG. 3 described later), and moves the pointer (second hand) by the rotation of the rotor RT. The rotor RT is a two-pole magnetized disk-shaped rotating body, magnetized with a north pole and a south pole in the radial direction. The stator ST is made of a soft magnetic material, and is wound with a single-phase coil C. Single phase means that there is one coil, and two terminals (terminals O1, O2) for inputting each pulse described later.

[Overview of the electronic watch 100: Reference signal generating circuit 2]
The reference signal generating circuit 2 includes an oscillation circuit 21 that generates a reference clock by the oscillation of a crystal oscillator (not shown), and a frequency dividing circuit 22 that divides the frequency of the reference signal from the oscillation circuit 21 .

[Overview of the electronic watch 100: normal drive pulse generating circuit 3]
The normal drive pulse generating circuit 3 generates and outputs a normal drive pulse SP based on the reference signal output from the reference signal generating circuit 2. The normal drive pulse SP is output to drive the hands one step every unit second (exact second, 1 [sec]). Fig. 2(a) shows an example in which a normal drive pulse SP including a plurality of single pulses output intermittently every 0.5 [ms] and having an output period of 4 [ms] is output every unit second.

[Overview of the electronic watch 100: correction drive pulse generating circuit 4]
The correction drive pulse generating circuit 4 generates and outputs a correction drive pulse FP based on the reference signal output from the reference signal generating circuit 2. The correction drive pulse FP is a pulse that is output to forcibly rotate the rotor RT of the step motor 8 when the step motor 8 is not rotating or when it is uncertain whether it has rotated or not. Fig. 2(d) shows a correction drive pulse FP that is output 32 [ms] after the start of output of the normal drive pulse SP and has an output period of 7 [ms].

[Overview of the electronic watch 100: rotation detection pulse generating circuit 5]
The rotation detection pulse generating circuit 5 generates and outputs a rotation detection pulse based on the reference signal output from the reference signal generating circuit 2. The rotation detection pulse is output to detect whether or not the rotor RT of the step motor 8 has rotated.

[Overview of the electronic watch 100: rotation detection circuit 9]
The rotation detection circuit 9 includes a judgment circuit 90. The judgment circuit 90 has a first judgment unit 91 and a second judgment unit 92. The first judgment unit 91 judges whether or not an induced voltage (detection value) equal to or greater than a threshold value Vth, which is a second threshold, is detected in the first detection mode. The second judgment unit 92 judges whether or not an induced voltage (detection value) equal to or greater than a threshold value Vth, which is a third threshold, is detected in the second detection mode.

The rotation detection circuit 9 outputs the judgment result by the judgment circuit 90 to the selector 6 and the drive rank selection circuit 10. Specifically, the rotation detection circuit 9 detects an induced voltage (detection value) equal to or greater than the threshold value Vth as a rotation detection signal, and outputs the rotation detection signal to the selector 6 and the drive rank selection circuit 10.

When the normal drive pulse SP is supplied to the coil C of the step motor 8, the stator ST is magnetized and the rotor RT vibrates, gradually decreasing the amplitude. The damped vibration of the rotor RT at this time causes a change in magnetic flux to the coil C, which generates a back electromotive force due to electromagnetic induction and causes an induced current (back electromotive current) to flow in the coil C. After the normal drive pulse SP is output, the rotation detection circuit 9 performs a rotation detection operation to detect whether the rotor RT of the step motor 8 has rotated or not, based on the induced voltage generated in the coil C.

In the following explanation, the determination by the rotation detection circuit 9 that the rotor RT of the step motor 8 has rotated will be referred to as a "rotation determination," and the determination that it is not rotating will be referred to as a "non-rotation determination."

In the first embodiment, an example of rotation detection operation is described in which rotation detection is performed in a first detection mode and a second detection mode that is started when a predetermined condition is satisfied in the first detection mode.

The second detection mode detects that rotation has been successful, i.e., that the rotor RT has crossed the magnetic potential peak. By performing the first detection mode before the second detection mode, it is possible to prevent a signal that has exceeded the magnetic potential from being mistakenly detected as a rotation detection signal even when the rotor RT has not yet finished rotating. In other words, in the first embodiment, rotation detection can be performed with high accuracy by performing rotation detection in two stages, the first detection mode and the second detection mode.

Figure 2(b) shows rotation detection pulses B5 to B14 output by the rotation detection pulse generating circuit 5 in the first detection mode. The numbers 5 to 14 of the rotation detection pulses B5 to B14 correspond to the time elapsed from the point when the output of the normal drive pulse SP begins. That is, the rotation detection pulses B5 to B14 shown in Figure 2(b) are pulses with an output interval of 0.5 [ms], which begin to be output 5 [ms] after the point when the output of the normal drive pulse SP begins, and end 14 [ms] later. Note that, since the first detection mode ends with the transition to the second detection mode, it is preferable to end the output of the rotation detection pulses B5 to B14 when the first detection mode ends.

FIG. 2(c) also shows rotation detection pulses F6.5 to F14 output by the rotation detection pulse generating circuit 5 in the second detection mode. The numbers 6.5 to 14 among the rotation detection pulses F6.5 to F14 correspond to the elapsed time from the point at which the output of the normal drive pulse SP begins. In other words, the rotation detection pulses F6.5 to F14 are pulses with an output interval of 0.5 ms, with output commencing 6.5 ms after the point at which the output of the normal drive pulse SP begins, and ending 14 ms later. It is preferable that the output of the rotation detection pulses F6.5 to F14 ends when the second detection mode ends.

In the first embodiment, the rotation detection pulses B5 to B14 are output to the terminal of the coil C opposite to the terminal to which the normal drive pulse SP is output. That is, when the normal drive pulse SP is output to the terminal O1 of the coil C to move the hands, the rotation detection pulses B5 to B14 are output to the terminal O2 of the coil C. The rotation detection circuit 9 then detects the induced voltage generated by the free vibration of the rotor RT after the normal drive pulse SP is output by suddenly changing the impedance of the closed loop including the coil C.

On the other hand, the rotation detection pulses F6.5 to F14 are output to the same terminal of coil C as the terminal to which the normal drive pulse SP is output. In other words, when the normal drive pulse SP is output to terminal O1 of coil C to move the hands, the rotation detection pulses F6.5 to F14 are output to terminal O1 of coil C. Then, the rotation detection circuit 9 detects the induced voltage generated by the free vibration of the rotor RT after the normal drive pulse SP is output by suddenly changing the impedance of the closed loop including coil C.

[Overview of the Electronic Timepiece 100: Selector 6]
The selector 6 selects whether to output a normal driving pulse SP, a correction driving pulse FP, or a rotation detection pulse based on the detection result of the rotation detection circuit 9 , and outputs the selected pulse to the driver circuit 7 .

[Overview of the electronic watch 100: driver circuit 7]
The driver circuit 7 outputs a signal (drive waveform) corresponding to the pulse input from the selector 6 to terminals O 1 and O 2 of the coil C of the step motor 8 .

[Overview of the electronic watch 100: drive rank selection circuit 10]
The drive rank selection circuit 10 selects the drive rank of the normal drive pulse SP and controls the normal drive pulse generation circuit 3. The drive rank corresponds to the duty ratio of the normal drive pulse SP. The larger the duty ratio, the greater the amount of current supplied to the coil C, and the greater the driving force of the step motor 8. The duty ratio indicates the proportion of the normal drive pulse SP that is output within a given period.

For example, it is preferable to prepare in advance 8/32, 16/32, 24/32, and 32/32 as duty ratios for the normal drive pulse SP. The higher the duty ratio, the stronger the driving force of the pulse. In other words, among the normal drive pulses SP with duty ratios of 8/32, 16/32, 24/32, and 32/32, the normal drive pulse SP with a duty ratio of 32/32 has the maximum driving force (driving rank), and the normal drive pulse SP with a duty ratio of 8/32 has the minimum driving force.

When the rotation detection circuit 9 judges that rotation has occurred, the drive rank selection circuit 10 maintains the drive rank of the normal drive pulse SP output by the normal drive pulse generation circuit 3. However, when the state in which the drive rank is maintained reaches a predetermined number of times, the drive rank selection circuit 10 lowers the drive rank of the normal drive pulse SP output by the normal drive pulse generation circuit 3. This is because the drive force of the normal drive pulse SP may be stronger than necessary, and power may be consumed unnecessarily. In the first embodiment, when the rotation judgment is counted 256 times in a row, the drive rank of the normal drive pulse SP is lowered by one rank (see FIG. 5 described later). Note that this is just an example and is not limited to 256 times.

When the rotation detection circuit 9 determines that the rotor RT is not rotating, the drive rank selection circuit 10 outputs the correction drive pulse FP from the correction drive pulse generation circuit 4 and raises the drive rank of the normal drive pulse SP output from the normal drive pulse generation circuit 3. This is because the drive force of the normal drive pulse SP currently being output may be weak. However, if the normal drive pulse SP currently being output is at the maximum rank, it may be lowered to the minimum rank. This is because the drive force may be too strong, and even if the rotor RT can rotate normally with sufficient force, a non-rotation determination may be made during rotation detection. In particular, when the drive rank is at the maximum rank, it is highly likely that the drive rank has increased due to a temporary increase in load. Therefore, it is necessary to return to an appropriate drive rank, but in order to lower the drive rank by one rank, it is necessary to count the rotation determination 256 times, which takes time and increases power consumption, so it is better to set it to the minimum drive rank once and then gradually raise the drive rank until a rotation determination is made.

[Circuit configuration of driver circuit]
Next, the circuit configuration of the driver circuit in the first embodiment will be specifically described with reference to Fig. 3. Fig. 3 is a circuit diagram showing the driver circuit and the rotation detection circuit in the first embodiment. In Fig. 3, the gate terminal of each transistor is indicated by "G", the drain terminal is indicated by "D", and the source terminal is indicated by "S". In the first embodiment, each transistor functions as a switch.

The driver circuit 7 is composed of a first driver circuit 71 and a second driver circuit 72. The first driver circuit 71 includes a P-channel MOS transistor P1 (hereinafter, transistor P1) and an N-channel MOS transistor N1 (hereinafter, transistor N1) that are complementary connected. The second driver circuit 72 similarly includes a P-channel MOS transistor P2 (hereinafter, transistor P2) and an N-channel MOS transistor N2 (hereinafter, transistor N2) that are complementary connected.

The source terminal of transistor P1 is connected to a reference voltage VDD, which is a high reference voltage, and the source terminal of transistor N1 is connected to a reference voltage VSS, which is a low reference voltage. Similarly, the source terminal of transistor P2 is connected to reference voltage VDD, and the source terminal of transistor N2 is connected to reference voltage VSS.

The reference voltage VSS and the reference voltage VDD are based on the power supply voltage of the power supply 1. The reference voltage VSS is a voltage lower than the reference voltage VDD. For example, when a negative power supply is used, the reference voltage VDD may be 0 [V] and the reference voltage VSS may be a negative voltage, and when a positive power supply is used, the reference voltage VDD may be a positive voltage and the reference voltage VSS may be 0 [V].

The drain terminals of transistors P1 and N1 of the first driver circuit 71 are connected to one terminal O1 of the coil C. The drain terminals of transistors P2 and N2 of the second driver circuit 72 are connected to the other terminal O2 of the coil C.

Although not shown in FIG. 3, the gate terminals of the transistors P1, N1, P2, and N2 are connected to the selector 6. The normal drive pulse SP, correction drive pulse FP, and rotation detection pulse selected by the selector 6 are input to the driver circuit 7, and are output from the driver circuit 7 to the step motor 8.

[Driver Circuit Operation]
Next, the operation of the driver circuit 7 will be described with reference to Fig. 3 and Fig. 4. Here, the operation of the driver circuit 7 when performing normal hand movement will be described. Fig. 4 is a diagram for explaining the ON/OFF control of the driver circuit and the rotation detection circuit in the first embodiment.

First, when the normal drive pulse SP is selected by the selector 6, transistors P1 and N2 are turned ON and the other transistors are turned OFF (see the upper part of "SP output" in Figure 4). Next, transistors N1 and P2 are turned ON and the other transistors are turned OFF (see the lower part of "SP output" in Figure 4). By alternately performing this ON/OFF control, the stator ST of the step motor 8 is alternately reversed in magnetization, causing the rotor RT to rotate. The hands then move in conjunction with the rotation of the rotor RT.

[Configuration of rotation detection circuit]
Next, the configuration of the rotation detection circuit in the first embodiment will be specifically described with reference to FIG.

The rotation detection circuit 9 includes a detection resistor R1 which is a first detection resistor, a detection resistor R2 which is a second detection resistor, an N-channel MOS transistor TN1 (hereinafter, transistor TN1) (first switch), an N-channel MOS transistor TN2 (hereinafter, transistor TN2) (second switch), and a determination circuit 90. It is preferable that the resistance values of the detection resistors R1 and R2 are equal.

The source terminals of transistors TN1 and TN2 are connected to a reference voltage VSS. The drain terminal of transistor TN1 is connected to one end of detection resistor R1, and the drain terminal of transistor TN2 is connected to one end of detection resistor R2.

The other end of the detection resistor R1 is connected to the drain terminals of the transistors P1 and N1 (i.e., the output terminal of the first driver circuit 71) and the inverter INV1 of the judgment circuit 90. The other end of the detection resistor R2 is connected to the drain terminals of the transistors P2 and N2 (i.e., the output terminal of the second driver circuit 72) and the inverter INV2 of the judgment circuit 90.

The inverters INV1 and INV2 may be C-MOS inverter circuits with a threshold value Vth. When the reference voltage VDD is 0 V, the threshold value Vth may be 1/2 the reference voltage VSS. In the first embodiment, an example in which the determination circuit 90 includes an inverter is described, but the present invention is not limited to this and may include, for example, an operational amplifier.

The inverter INV1 is connected between the detection resistor R1 and the terminal O1 of the coil C, and determines whether an induced voltage equal to or greater than the threshold Vth is detected in the detection resistor R1. Similarly, the inverter INV2 is connected between the detection resistor R2 and the terminal O2 of the coil C, and determines whether an induced voltage equal to or greater than the threshold Vth is detected in the detection resistor R2.

[Operation when rotation is detected]
Next, the operation at the time of detecting rotation in the first embodiment will be described with reference to FIG. 3 and FIG.

As described above with reference to "SP output" in Figure 4, the rotor RT is rotated by controlling the ON/OFF of transistors P1, P2, N1, and N2, and then the rotor RT starts to vibrate freely. At this time, the rotation detection pulse is selected by the selector 6, and the rotation detection pulse is output to the driver circuit 7, causing the impedance value of coil C of the step motor 8 to change suddenly, and the generated induced current is detected by terminals O1 and O2 of coil C.

Specifically, transistors P2 and TN1 are turned ON while the other transistors are turned OFF, and then transistors P1 and TN2 are turned ON while the other transistors are turned OFF, and this control is alternately switched (see "First detection mode" and "Second detection mode" in FIG. 4). The detected voltage waveform and the determination of whether the rotor RT is rotating will be described later with reference to FIG. 6 to FIG. 8.

Here, the transistors TN1 and TN2 and the detection resistors R1 and R2 have the function of generating a rotation detection signal based on the rotation detection pulse. A pair of signals input to the inverters INV1 and INV2 to which the detection resistors R1 and R2 are connected are rotation detection signals from the rotor RT of the step motor 8. In other words, the rotation detection signal is generated as an induced voltage across the detection resistors R1 and R2 when an induced current from the rotor RT of the step motor 8 flows through the detection resistors R1 and R2. The judgment circuit 90 inputs the induced voltage generated in the detection resistors R1 and R2 and judges whether it has exceeded an internally set threshold value Vth.

In the first detection mode, the inverter INV1 connected to the terminal O1 of the coil C is operated. When a rotation detection signal equal to or greater than the threshold Vth is detected a predetermined number of times in the first detection mode, the first detection mode is stopped and the mode transitions to the second detection mode. In the first embodiment, when a rotation detection signal equal to or greater than the threshold Vth is detected three times, the first detection mode is stopped and the mode transitions to the second detection mode.

In the second detection mode, the inverter INV2 connected to the terminal O2 of the coil C is operated. In the second detection mode, when a rotation detection signal equal to or greater than the threshold Vth is detected a predetermined number of times, a rotation determination is made, and when it is not detected the predetermined number of times, a non-rotation determination is made. In the first embodiment, when a rotation detection signal equal to or greater than the threshold Vth is detected twice, a rotation determination is made, and when it is detected 0 or 1 time, a non-rotation determination is made.

In the first embodiment, the threshold value Vth used in the first detection mode and the second detection mode is the same, but this is not limited to the above and different threshold values may be used.

[Features of the circuit configuration of the first embodiment]
Fig. 13 is a circuit diagram of a driver circuit and a rotation detection circuit of a conventional example, and is a diagram to be referred to for comparison with the first embodiment shown in Fig. 3. As shown in Fig. 13, in the conventional circuit, the output terminal of the step motor 8 is pulled up to the reference voltage VDD via detection resistors R1 and R2.

On the other hand, as shown in FIG. 3, in the first embodiment, the drain terminals of each transistor included in the driver circuit 7, i.e., the output terminal of the driver circuit 7, are connected to the reference voltage VSS via the detection resistors R1 and R2. In other words, the output terminal of the step motor 8 is pulled down to the reference voltage VSS via the detection resistors R1 and R2.

Here, during the rotation detection operation, some of the magnetic flux generated by the free vibration of the rotor RT may not pass through the coil C and may not contribute to the detection current. However, in the circuit configuration of the first embodiment, the moment the transistor TN1 is turned on, a current flows from the reference voltage VDD connected to the source terminal of the transistor P2 to the reference voltage VSS connected to the drain terminal of the transistor TN1, and the magnetic flux generated around the coil C thereby interferes with the magnetic flux generated by the free vibration of the rotor RT, and the magnetic flux that would not have passed through the coil C originally passes through the coil C. Similarly, the moment the transistor TN2 is turned on, a current flows from the reference voltage VDD connected to the source terminal of the transistor P1 to the reference voltage VSS connected to the drain terminal of the transistor TN2, and the magnetic flux generated around the coil C thereby interferes with the magnetic flux generated by the free vibration of the rotor RT, and the magnetic flux that would not have passed through the coil C originally passes through the coil C. This is expected to have the effect of increasing the induced voltage to be detected.

As described above, in the configuration of the first embodiment, the induced voltage detected can be made larger than in the conventional configuration, and the induced voltage is more likely to be equal to or greater than the threshold voltage Vth. As a result, the rotation detection circuit 9 can more easily determine rotation. In other words, the detection sensitivity of the rotation determination can be increased compared to the configuration in which the output terminal of the step motor 8 is pulled up to the reference voltage VDD via the detection resistors R1 and R2 (the conventional example in FIG. 13).

By increasing the detection sensitivity of the rotation judgment, it is possible to suppress the rotor RT from being judged as not rotating even though it is rotating, and the correction drive pulse FP is output. In other words, it is possible to suppress unnecessary increase in power consumption. In particular, when an inverter is used for the judgment circuit 90 and the voltage threshold Vth for judging the rotation detection is set to 1/2 of the power supply voltage V, the threshold Vth becomes larger as the power supply voltage increases, making it difficult to judge the rotation, so it is effective to increase the detection sensitivity of the rotation judgment according to this embodiment. Therefore, when the power supply voltage is equal to or higher than a predetermined value (first threshold), the rotation detection may be performed using the transistors TN1 and TN2. Also, when the power supply voltage is lower than the predetermined value (first threshold), the rotation detection may be performed without using the transistors TN1 and TN2. In this case, the current generated in the coil C due to the rotation of the rotor RT is connected to either VDD or VSS via the parasitic capacitance (not shown) of the driver circuit or the judgment circuit. At this time, the detection sensitivity can be lower than when the transistors TN1 and TN2 are used.

[Rank setting control of normal drive pulse]
Next, the rank setting control of the normal driving pulse SP based on the rotation detection operation in the first embodiment will be described with reference to Fig. 5. Fig. 5 is a flow chart showing the rank setting control of the normal driving pulse based on the rotation detection operation in the first embodiment. Note that Fig. 5 shows the operation every second.

First, the selector 6 selects and outputs the normal drive pulse SP exactly at the second (step ST1).

Then, 5 ms after the second, the rotation detection operation starts (step ST2, see FIG. 2(b)). In the rotation detection operation, the first detection mode is performed first. In the first detection mode, the selector 6 selects and outputs a rotation detection pulse. Then, the rotation detection circuit 9 detects the induced voltage generated in the coil C based on the rotation detection pulse.

Meanwhile, the rotation detection circuit 9 starts a judgment operation by the first judgment unit 91. If the first judgment unit 91 judges that the rotation detection signal has been detected three times (step ST3: Y), the rotation detection circuit 9 transmits an instruction to the selector 6 to end the first detection mode and transmits an instruction to transition to the second detection mode.

On the other hand, if the first judgment unit 91 judges that the rotation detection signal has been detected less than three times (step ST3: N), the rotation detection circuit 9 performs a non-rotation judgment, sends an instruction to the selector 6 to end the first detection mode, and selects and outputs the correction drive pulse FP (step ST5).

When the second detection mode is entered (step ST3: Y), the selector 6 selects and outputs the rotation detection pulse. Then, the rotation detection circuit 9 detects the induced voltage generated in the coil C based on the rotation detection pulse.

Meanwhile, the rotation detection circuit 9 starts a judgment operation by the second judgment unit 92. If the second judgment unit 92 judges that the rotation detection signal has been detected twice (step ST4: Y), the rotation detection circuit 9 transmits an instruction to end the second detection mode to the selector 6, and acquires the number of times that rotation judgment has been made at that time (step ST9).

In step ST4, if the second judgment unit 92 judges that the rotation detection signal has been detected less than twice (step ST4: N), the rotation detection circuit 9 performs a non-rotation judgment, transmits an instruction to end the second detection mode to the selector 6, and selects and outputs the correction drive pulse FP (step ST5).

After the correction drive pulse FP is output in step ST5, the drive rank selection circuit 10 determines whether the drive rank of the normal drive pulse SP output immediately before is the maximum rank (step ST6). If the drive rank is the maximum (step ST6: Y), the drive rank selection circuit 10 lowers the drive rank of the normal drive pulse SP to be output next to the minimum rank (ST7). The number of rotation determinations is then reset (step ST12). On the other hand, if the drive rank is not the maximum (step ST6: N), the drive rank selection circuit 10 increases the drive rank of the normal drive pulse SP to be output next by one rank (step ST8). The number of rotation determinations is then reset (step ST12).

After the second detection mode ends, if the number of rotation determinations acquired in step ST9 is 256 (step ST10: Y), the drive rank selection circuit 10 reduces the drive rank of the normal drive pulse SP to be output next by one rank (step ST11). After that, the number of rotation determinations is reset (step ST12).

On the other hand, if the number of rotation determinations obtained does not reach 256 (step ST10: N), the drive rank selection circuit 10 maintains the drive rank of the normal drive pulse SP that will be output next time.

[Example of detected waveform]
Next, referring to Fig. 6 and Fig. 7, the waveforms detected in the rotation detection operation of the first embodiment will be specifically described. Fig. 6 is a waveform diagram showing an example of a case where rotation is determined in the rotation detection operation of the first embodiment. Fig. 7 is a waveform diagram showing an example of a case where non-rotation is determined in the rotation detection operation of the first embodiment. Figs. 6 and 7 show an example of a circuit configuration in which the output terminal of the step motor 8 is pulled down to the reference voltage VSS via the detection resistors R1 and R2, that is, the circuit configuration in the first embodiment shown in Fig. 3 is adopted. Figs. 6(a) and 7(a) show an example of a current waveform induced in the coil C. Figs. 6(b) and 7(b) show an example of a rotation detection signal (induced voltage) detected in the second detection mode. Figs. 6(c) and 7(c) show an example of a rotation detection signal (induced voltage) detected in the first detection mode.

The waveform c1 shown in FIG. 6(a) is the current waveform when the normal drive pulse SP is output to the coil C. When the output of the normal drive pulse SP ends, the rotor RT enters a free vibration state, and the current waveform becomes the induced current waveform shown in c2, c3, and c4.

When 5 ms have elapsed since the start of output of the normal drive pulse SP, in the first detection mode, the rotation detection pulse B5 (see FIG. 2) is output to terminal O2 of coil C. As shown in FIG. 6(a), when 5 ms have elapsed, the current waveform is in the region of current waveform c2, and the current value is in the negative direction. Therefore, as shown in FIG. 6(c), the induced voltage V5 generated by the rotation detection pulse B5 does not exceed the threshold value Vth of inverter INV2.

When 6.5 ms have elapsed since the start of output of the normal drive pulse SP, the current waveform enters the region of current waveform c3, and the current value changes to the positive direction. As shown in FIG. 6(c), the induced voltage V6.5 generated by the rotation detection pulse B6.5 becomes a rotation detection signal that exceeds the threshold value Vth. Similarly, at 7 ms and 7.5 ms, the current waveform is in the region of current waveform c3, and the induced voltages V7 and V7.5 generated by the rotation detection pulses B7 and B7.5 become rotation detection signals that exceed the threshold value Vth. When the three induced voltages V6.5, V7, and V7.5 exceed the threshold value Vth, the first detection mode ends and the mode switches to the second detection mode.

In the second detection mode, when the next rotation detection pulse after the last rotation detection pulse output in the first detection mode is output, that is, when 8 ms has elapsed from the start of output of the normal drive pulse SP, a rotation detection pulse F8 (see FIG. 2(c)) is output to terminal O1 of coil C.

As shown in FIG. 6(a), after 8 ms has elapsed, the current waveform is in the region of current waveform c3, and the current value is in the positive direction. Therefore, as shown in FIG. 6(b), the induced voltage V8 generated by the rotation detection pulse F8 does not exceed the threshold value Vth.

As shown in FIG. 6(a), after 9.5 ms, the current waveform is in the region of the current waveform c4, and the current value changes to the negative direction. As shown in FIG. 6(b), the induced voltage V9.5 generated by the rotation detection pulse B9.5 becomes a rotation detection signal that exceeds the threshold Vth. Similarly, even at 10 ms, the current waveform is in the region of the current waveform c4, and the induced voltage V10 generated by the rotation detection pulse B10 becomes a rotation detection signal that exceeds the threshold Vth. As the two induced voltages V9.5 and V10 exceed the threshold Vth, the determination circuit 90 makes a rotation determination and ends the second detection mode. Then, without outputting the correction drive pulse FP, the drive rank selection circuit 10 maintains the drive rank of the normal drive pulse SP that is output next time.

Next, referring to FIG. 7, the waveform when non-rotation is determined will be described. FIG. 7(a) shows an example in which a current waveform with a low peak value and a smoother current waveform is detected compared to FIG. 6(a). Note that FIG. 7, like FIG. 6, is an example in which the circuit of the first embodiment shown in FIG. 3 is used.

The waveform c1 shown in FIG. 7(a) is the current waveform when the normal drive pulse SP is output to the coil C. When the output of the normal drive pulse SP ends, the rotor RT enters a free vibration state, and the current waveform becomes the induced current waveform shown in c2 and c5.

As shown in FIG. 7(a), at 5 ms the current waveform is in the region of current waveform c2, and the current value is in the negative direction. Therefore, as shown in FIG. 7(c), the induced voltage V5 generated by the rotation detection pulse B5 does not exceed the threshold value Vth of the inverter INV2.

6 ms after the start of output of the normal drive pulse SP, the current waveform enters the region of current waveform c5, and the current value changes to the positive direction. As shown in FIG. 7(c), the induced voltage V6 generated by the rotation detection pulse B6 becomes a rotation detection signal that exceeds the threshold value Vth. Similarly, at 6.5 ms and 7 ms, the current waveform is in the region of current waveform c5, and the induced voltages V6 and V6.5 generated by the rotation detection pulses B6 and B6.5 become rotation detection signals that exceed the threshold value Vth. When the three induced voltages V6, V6.5, and V7 exceed the threshold value Vth, the first detection mode ends and the mode switches to the second detection mode.

In the second detection mode, when the next rotation detection pulse after the last rotation detection pulse output in the first detection mode is output, that is, when 7.5 ms have elapsed from the start of output of the normal drive pulse SP, a rotation detection pulse F7.5 (see FIG. 2(c)) is output to terminal O1 of coil C.

As shown in FIG. 7(a), the current waveform c5 maintains a positive current value and never becomes a negative current value. Therefore, as shown in FIG. 7(b), the induced voltage V7.5 generated by the rotation detection pulse F7.5 and subsequent induced voltages never exceed the threshold value Vth.

Therefore, the second determination unit 92 performs a non-rotation determination and ends the second detection mode. As a result, the selector 6 selects the correction drive pulse FP and outputs the correction drive pulse FP to the step motor 8. In addition, the drive rank selection circuit 10 increases the drive rank of the normal drive pulse SP to be output next time by one rank.

Now, referring to Figure 8, we will explain the waveforms detected during rotation detection operation when the conventional circuit configuration is adopted. Figure 8 is a diagram showing an example of a waveform detected during rotation detection operation when the conventional circuit configuration, i.e., the circuit configuration shown in Figure 13, is adopted.

As shown in FIG. 8(a), the current waveform induced in coil C is the same as that shown in FIG. 6(a). On the other hand, the induced voltage generated across both ends of detection resistors R1 and R2 is smaller than that shown in FIG. 6(b) and FIG. 6(c). This is because in the conventional example, the output terminal of step motor 8 is pulled up to reference voltage VDD via detection resistors R1 and R2, and the induced voltage generated across both ends of detection resistors R1 and R2 does not become large as in the first embodiment.

Therefore, in the example shown in FIG. 8, in the second detection mode, a rotation detection signal exceeding the threshold value Vth cannot be detected, and a non-rotation determination is made. As a result, the correction drive pulse generation circuit 4 outputs a correction drive pulse FP, and the drive rank of the normal drive pulse SP output next time by the drive rank selection circuit 10 is increased by one rank. Thus, in the example shown in FIG. 8, even though the current waveform generated by the free vibration of the rotor RT is the same, a non-rotation determination is made, and power consumption increases unnecessarily.

As described above, in the first embodiment, a configuration that can prevent the rotor RT from being determined to be non-rotating even though it is rotating can be realized with a simple circuit configuration. As a result, it is possible to prevent the unnecessary output of the correction drive pulse FP from increasing power consumption. The configuration of the first embodiment is particularly effective when driving the step motor 8 with low power consumption.

Second Embodiment
Next, an electronic timepiece 200 according to a second embodiment will be described with reference to Figs. 9 to 11. Fig. 9 is a block diagram showing an outline of the overall configuration of the electronic timepiece according to the second embodiment. Fig. 10 is a circuit diagram showing a driver circuit and a rotation detection circuit in the second embodiment. Fig. 11 is a flow chart showing rank setting control of a normal drive pulse based on a rotation detection operation in the second embodiment. Note that the same reference numerals are used for configurations similar to those described in the first embodiment, and descriptions thereof will be omitted.

The electronic watch 200 according to the second embodiment has a power supply voltage detection circuit 110 and a detection sensitivity selection circuit 120 in addition to the configuration of the electronic watch 100 according to the first embodiment. It also has a variable power supply 11 instead of the power supply 1.

The variable power supply 11 is a power supply whose power supply voltage V fluctuates. For example, the variable power supply 11 may be a secondary battery such as a solar cell. The power supply voltage detection circuit 110 is a circuit that detects the power supply voltage V of the variable power supply 11. The detection sensitivity selection circuit 120 is a circuit that selects the detection sensitivity in the rotation detection circuit 9.

As shown in FIG. 10, the driver circuit 7 of the second embodiment has the same configuration as that described in the first embodiment.

The rotation detection circuit 209 of the second embodiment has four transistors that function as switches. Specifically, the rotation detection circuit 209 has an N-channel MOS transistor TN1 (hereinafter, transistor TN1) as a first switch whose drain terminal is connected to one end of the detection resistor R1, and a P-channel MOS transistor TP1 (hereinafter, transistor TP1) as a third switch. The rotation detection circuit 209 also has an N-channel MOS transistor TN2 as a second switch whose drain terminal is connected to one end of the detection resistor R2, and a P-channel MOS transistor TP2 (hereinafter, transistor TP2) as a fourth switch.

The source terminal of transistor TN1 is connected to a reference voltage VSS, while the source terminal of transistor TP1 is connected to a reference voltage VDD.

The source terminal of transistor TN2 is connected to reference voltage VSS, while the source terminal of transistor TP2 is connected to reference voltage VDD.

In the second embodiment, the detection sensitivity selection circuit 120 selects either the transistor TN1 and the transistor TN2, or the transistor TP1 and the transistor TP2, as the switch to be used during the rotation detection operation based on the power supply voltage V detected by the power supply voltage detection circuit 110.

In the second embodiment, the threshold value Vth is set according to the reference voltage VSS, and specifically, is 1/2 the reference voltage VSS. Therefore, when the power supply voltage V of the variable power supply 11 is high, the threshold value Vth becomes large accordingly, making it difficult to determine rotation.

Therefore, in the second embodiment, the detection sensitivity is increased when the power supply voltage V is relatively high.

When the power supply voltage V detected by the power supply voltage detection circuit 110 is greater than 3.0 [V], the detection sensitivity selection circuit 120 uses transistors TN1 and TN2 during rotation detection operation. In this case, the rotation detection circuit 209 becomes equivalent to the rotation detection circuit 9 of the first embodiment described with reference to FIG. 3. In other words, the detection sensitivity of the rotation determination becomes higher.

On the other hand, when the power supply voltage V detected by the power supply voltage detection circuit 110 is 2.0 V or less, the detection sensitivity selection circuit 120 uses transistors TP1 and TP2 during rotation detection operation. In this case, the rotation detection circuit 209 becomes equivalent to the conventional rotation detection circuit shown in FIG. 13.

The rank setting control of the normal drive pulse based on the rotation detection operation in the second embodiment will be described with reference to FIG. 11. FIG. 11 is a flowchart showing the rank setting control of the normal drive pulse based on the rotation detection operation in the second embodiment. Note that FIG. 11 shows the operation every second.

First, the selector 6 selects and outputs the normal drive pulse SP exactly at the second (step ST1).

Then, 5 ms after the second, the rotation detection operation starts (step ST2, see FIG. 2(b)). In the rotation detection operation of the second embodiment, first, the power supply voltage V of the variable power supply 11 is acquired by the power supply voltage detection circuit 110.

If the acquired power supply voltage V is 2.0 [V] (fifth threshold) or less (step ST20: Y), the detection sensitivity selection circuit 120 selects the transistors TP1 and TP2 (step ST30). That is, the rotation of the rotor RT is detected by controlling the ON/OFF of the transistors TP1 and TP2. In this case, since the power supply voltage V is small, it is possible to appropriately determine the rotation detection by lowering the sensitivity of the rotation detection.

If the acquired power supply voltage V is greater than 2.0 [V] (step ST20: N) and less than or equal to 3.0 [V] (step ST21: Y), the detection sensitivity selection circuit 120 turns off all of the transistors TP1, TP2, TN1, and TN2 (step ST31). In this case, the current generated in the coil C by the rotation of the rotor RT is connected to either VDD or VSS via the parasitic capacitance (not shown) of the driver circuit or the judgment circuit. Since the resistance component of this parasitic capacitance is sufficiently large compared to the detection resistors R1 and R2, the detection sensitivity is intermediate between the detection sensitivity when the transistors TP1 and TP2 are selected and the detection sensitivity when the transistors TN1 and TN2 are selected. In this way, when the power supply voltage V is an intermediate value, the rotation detection can be appropriately judged by setting the rotation detection to the intermediate detection sensitivity.

If the acquired power supply voltage V is greater than 3.0 [V] (fourth threshold) (step ST21: N), the detection sensitivity selection circuit 120 selects the transistors TN1 and TN2 (step ST32). That is, the rotation of the rotor RT is detected by controlling the ON/OFF of the transistors TN1 and TN2. In this case, since the power supply voltage V is large, it is possible to appropriately determine the rotation detection by increasing the sensitivity of the rotation detection.

Below, steps ST3 to ST12 shown in FIG. 11 are the same as the control described in FIG. 5, so the description will be omitted.

In the second embodiment described above, even if the power supply voltage V of the variable power supply 11 fluctuates, it is possible to perform rotation detection with high accuracy. In the second embodiment, the detection sensitivity selection circuit 120 selects each transistor based on the power supply voltage V, but it may also select based on the duty ratio. This is because there is a certain degree of correlation between the power supply voltage V and the duty ratio, and when the power supply voltage V is high, the duty ratio is likely to be small, and when the power supply voltage V is low, the duty ratio is likely to be large. Therefore, when the duty ratio is equal to or greater than a certain threshold (seventh threshold), the detection circuit selection circuit 120 may select the transistors TP1 and TP2, and when the duty ratio is smaller than a certain threshold (sixth threshold), the detection circuit selection circuit 120 may select the transistors TN1 and TN2.

[Modification of the second embodiment]
Next, a modified example of the second embodiment will be described with reference to Fig. 12. Fig. 12 is a circuit diagram showing a driver circuit and a rotation detection circuit in a modified example of the second embodiment. Note that the same reference numerals are used for configurations similar to those described in the first or second embodiment, and descriptions thereof will be omitted.

As shown in FIG. 12, the driver circuit 7 of the modified example of the second embodiment has the same configuration as that described in the second embodiment.

The rotation detection circuit 309 of the modified example of the second embodiment includes, in addition to the configuration shown in FIG. 10, a detection resistor R11, a P-channel MOS transistor TP11 (hereinafter, transistor TP11), and an N-channel MOS transistor TN11 (hereinafter, transistor TN11). Furthermore, the rotation detection circuit 309 includes a detection resistor R21, a P-channel MOS transistor TP21 (hereinafter, transistor TP21), and an N-channel MOS transistor TN21 (hereinafter, transistor TN21).

The resistance values of the detection resistors R1, R2, R11, and R21 may be the same or different.

One end of the detection resistor R11 is connected to the drain terminals of transistors TP11 and TN11, and the other end is connected to terminal O1 of coil C and inverter INV1.

One end of the detection resistor R21 is connected to the drain terminals of transistors TP21 and TN21, and the other end is connected to terminal O2 of coil C and inverter INV2.

In the rotation detection operation of the modified example of the second embodiment, for example, a combined resistance of the detection resistors R1 and R11 may be generated by simultaneously turning on the transistors TP1 and TP11. Similarly, a combined resistance of the detection resistors R1 and R11 may be generated by simultaneously turning on the transistors TN1 and TN11.

In a modified example of the second embodiment, the number of resistance value patterns of the detection resistor, i.e., the number of detection sensitivity patterns, can be increased, allowing for more accurate rotation detection.

In the above embodiments and modified examples, rotation detection for normal needle movement has been described, but the present invention is not limited to this and can also be applied to high-speed needle movement.

The above describes the embodiments and their modifications according to the present invention, but the specific configurations shown in these embodiments are shown as examples and are not intended to limit the technical scope of the present invention. Those skilled in the art may modify these disclosed embodiments as appropriate, and it should be understood that the technical scope of the invention disclosed in this specification includes such modifications.

1 Power supply, 11 Variable power supply, 2 Reference signal generating circuit, 21 Oscillating circuit, 22 Dividing circuit, 3 Normal driving pulse generating circuit, 4 Correction driving pulse generating circuit, 5 Rotation detection pulse generating circuit, 6 Selector, 7 Driver circuit, 71 First driver circuit, 72 Second driver circuit, 8 Step motor, 9, 209, 309 Rotation detection circuit, 90 Judgment circuit, 91 First judgment unit, 92 Second judgment unit, 10 Drive rank selection circuit, 100 Electronic clock, 110 Power supply voltage detection circuit, 120 Detection sensitivity selection circuit, C Coil, RT Rotor, ST Stator.

Claims (13)

a step motor including a rotor and a coil;
a drive pulse generating circuit that generates a drive pulse including a plurality of short pulses and outputs the drive pulse at a predetermined interval;
a driver circuit for driving the step motor based on the drive pulse ;
a rotation detection circuit including a first detection resistor, a second detection resistor, a first switch connected to one terminal of the coil via the first detection resistor, and a second switch connected to the other terminal of the coil via the second detection resistor, the rotation detection circuit detecting whether the rotor has rotated or not based on a back electromotive current generated by free vibration of the rotor during the period from when the output period of the drive pulse has elapsed until when the next drive pulse is output ;
having
the first switch and the second switch are connected to a first reference voltage;
the driver circuit includes a first driver circuit including a first driver switch connected to the one terminal, and a second driver circuit including a second driver switch connected to the other terminal;
the first driver switch and the second driver switch are coupled to at least a second reference voltage;
the driver circuit turns on the first driver switch or the second driver switch when the rotation detection circuit detects rotation.
Electronic clock. the second reference voltage is a high reference voltage;
the first reference voltage is a low reference voltage lower than the high reference voltage;
2. The electronic watch according to claim 1. A variable power supply whose power supply voltage fluctuates;
a power supply voltage detection circuit for detecting the power supply voltage;
having
the rotation detection circuit determines whether or not the rotor has rotated by using the first switch and the second switch when the power supply voltage is greater than a first threshold value during the rotation detection.
3. The electronic watch according to claim 2. the first switch is an N-channel MOS transistor having a drain terminal connected to the first sense resistor and a source terminal connected to the low reference voltage;
the second switch is an N-channel MOS transistor having a drain terminal connected to the second sense resistor and a source terminal connected to the low reference voltage;
4. The electronic watch according to claim 3. The rotation detection circuit includes:
a first determination unit connected between the first detection resistor and one end of the coil and configured to determine whether a detection value equal to or greater than a second threshold is detected in the first detection resistor;
a second determination unit connected between the second detection resistor and the other end of the coil and configured to determine whether a detection value equal to or greater than a third threshold is detected in the second detection resistor;
Including,
5. The electronic watch according to claim 2, wherein the electronic watch is a clock. the rotation detection circuit further includes a third switch connected to one terminal of the coil via the first detection resistor, and a fourth switch connected to the other terminal of the coil via the second detection resistor,
the third switch and the fourth switch are connected to the high reference voltage;
6. The electronic watch according to claim 2, wherein the electronic watch is a clock. a detection sensitivity selection circuit that selects whether to use the first switch and the second switch, or the third switch and the fourth switch, or whether to use neither of them during a rotation detection operation by the rotation detection circuit;
7. The electronic watch according to claim 6. A variable power supply whose power supply voltage fluctuates;
a power supply voltage detection circuit for detecting the power supply voltage;
having
the detection sensitivity selection circuit selects the first switch and the second switch when the power supply voltage is greater than a fourth threshold, and selects the third switch and the fourth switch when the power supply voltage is equal to or less than a fifth threshold.
8. The electronic watch according to claim 7. the detection sensitivity selection circuit selects the first switch and the second switch when a duty ratio of a normal drive pulse for normally moving the hands is smaller than a sixth threshold value, and selects the third switch and the fourth switch when the duty ratio is equal to or greater than a seventh threshold value.
8. The electronic watch according to claim 7. the third switch is a P-channel MOS transistor having a drain terminal connected to the first sense resistor and a source terminal connected to the high reference voltage;
the fourth switch is a P-channel MOS transistor having a drain terminal connected to the second detection resistor and a source terminal connected to the high reference voltage;
10. The electronic watch according to claim 6. the drive pulse generating circuit is a normal drive pulse generating circuit that generates and outputs a normal drive pulse for moving the hands normally;
a drive rank selection circuit that selects a drive rank of the normal drive pulse based on a detection result by the rotation detection circuit;
11. The electronic watch according to claim 1. the drive pulse generating circuit is a normal drive pulse generating circuit that generates and outputs a normal drive pulse for moving the hands normally;
a correction drive pulse generating circuit that generates and outputs a correction drive pulse having a larger drive force than the normal drive pulse when the rotation detection circuit determines that the rotor is not rotating;
11. The electronic watch according to claim 1. the second reference voltage is 0;
the first reference voltage is a negative voltage;
The electronic watch according to any one of claims 1 to 12 .

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