JP5927060B2 - Signal transmission circuit, integrated circuit, and electrical equipment including the same - Google Patents

Description

  The present invention relates to a signal transmission circuit, an integrated circuit, and an electric device including the same, and more particularly to a signal transmission technique for an analog signal.

  There is known a method of transmitting a pulse signal generated based on a signal to be transmitted using a pulse transformer, a photocoupler, or the like when the electric signal is transmitted while being electrically insulated.

  Japanese Patent Laying-Open No. 2010-10762 (Patent Document 1) discloses a signal transmission circuit device used for a power semiconductor drive circuit device, which transmits a control input signal using a pulse transformer, and the transmitted signal is a control input. A configuration including a self-diagnosis function for detecting and monitoring whether or not a signal is faithfully restored is disclosed.

JP 2010-10762 A

  When an analog signal is transmitted while being electrically insulated, a pulse signal is generated based on a comparison between the analog signal to be transmitted and a reference wave having a predetermined period and amplitude, and the pulse signal is used using a pulse transformer or the like. In some cases, it is transmitted and restored as a digital duty signal.

  In such an analog signal transmission configuration, the amplitude of the reference wave is generally set as appropriate in accordance with the rated usage range of the analog signal to be transmitted. However, for example, when a failure occurs in a sensor that generates an analog signal or a signal line from the sensor to the signal transmission circuit is short-circuited or disconnected, the analog signal input to the signal transmission circuit is May be outside the amplitude range.

  In this way, when the input analog signal is out of the amplitude range of the reference wave, if a temporary transmission failure of the pulse signal occurs due to noise or the like, the input analog signal There may be a case where the signal state does not match the output duty signal.

  The present invention has been made to solve such a problem, and an object thereof is to improve signal transmission accuracy in a signal transmission circuit that transmits an analog signal while being electrically insulated.

  The signal transmission circuit according to the present invention includes a pulse generation unit, first and second transmission units, and a latch circuit, and transmits an analog signal while being electrically insulated. The pulse generation unit generates and outputs first and second pulses based on a comparison between the analog signal and a predetermined reference wave. The first and second transmission units transmit the first and second pulses generated by the pulse generation unit while being electrically insulated. The latch circuit sets the output signal on according to the first pulse transmitted by the first transmission unit, and resets the output signal off according to the second pulse transmitted by the second transmission unit, An analog signal is output as a duty. The pulse generator outputs additional pulses for the first and second pulses when the increase or decrease of the amplitude of the reference wave is switched.

  Preferably, the pulse generation unit generates the first pulse when the amplitude of the reference wave coincides with the size of the analog signal while the amplitude of the reference wave increases, and the amplitude of the reference wave decreases. A path for generating a second pulse when the amplitude of the reference wave and the magnitude of the analog signal coincide with each other.

  Preferably, the pulse generation unit outputs an additional pulse for the first pulse when the amplitude of the reference wave is switched from increase to decrease, and the second is generated when the amplitude of the reference wave is switched from decrease to increase. Output additional pulses for the other pulses.

  Preferably, the amplitude of the reference wave increases or decreases within a predetermined range defined by the upper limit value and the lower limit value. When the reference wave amplitude reaches the upper limit value, the reference wave amplitude can be switched from increase to decrease, and when the reference wave amplitude reaches the lower limit value, the reference wave amplitude can be switched from decrease to increase. It is done.

  Preferably, when the magnitude of the analog signal exceeds the upper limit value, the pulse generation unit does not output an additional pulse for the first pulse even if the amplitude of the reference wave is switched from increase to decrease. .

  Preferably, when the magnitude of the analog signal falls below the lower limit value, the pulse generation unit does not output an additional pulse for the second pulse even when the amplitude of the reference wave is switched from decrease to increase. .

  Preferably, each of the first and second transmission units includes a transformer or a photocoupler.

  Preferably, the pulse generation unit outputs a plurality of continuous pulses as the first and second pulses.

  Preferably, the pulse generation unit stops the output of the first pulse while the amplitude of the reference wave is decreasing, and stops the output of the second pulse while the amplitude of the reference wave is increasing.

An integrated circuit according to the present invention is obtained by integrating the signal transmission circuit described above.
An electrical device according to the present invention includes the signal transmission circuit described above.

  The signal transmission circuit according to the present invention includes a pulse generation unit, first and second transmission units, and a latch circuit, and transmits an analog signal while being electrically insulated. The pulse generation unit generates and outputs first and second pulses based on a comparison between the analog signal and a predetermined reference wave. The first and second transmission units transmit the first and second pulses generated by the pulse generation unit while being electrically insulated. The latch circuit sets the output signal on according to the first pulse transmitted by the first transmission unit, and resets the output signal off according to the second pulse transmitted by the second transmission unit, An analog signal is output as a duty. The pulse generation unit outputs a plurality of continuous pulses as the first and second pulses. The pulse generator stops outputting the first pulse while the amplitude of the reference wave is decreasing, and stops outputting the second pulse while the amplitude of the reference wave is increasing.

  According to the present invention, signal transmission accuracy can be improved in a signal transmission circuit that transmits an analog signal while being electrically insulated.

1 is an overall block diagram of a motor drive system in which a signal transmission circuit according to the present embodiment is used. It is a functional block diagram which shows the detail of the temperature monitor circuit in FIG. It is a time chart for demonstrating the general method which transmits an analog signal by the comparison with a reference wave. It is a figure for demonstrating the problem in the signal transmission method of FIG. It is the 1st figure for demonstrating the signal transmission method at the time of using the signal transmission circuit according to Embodiment 1. FIG. FIG. 11 is a second diagram for illustrating a signal transmission method when the signal transmission circuit according to the first embodiment is used. FIG. 11 is a third diagram for illustrating a signal transmission method when the signal transmission circuit according to the first embodiment is used. FIG. 10 is a fourth diagram for illustrating a signal transmission technique when the signal transmission circuit according to the first embodiment is used. FIG. 10 is a first diagram for illustrating a signal transmission technique when a signal transmission circuit according to the second embodiment is used. FIG. 10 is a second diagram for illustrating a signal transmission technique when the signal transmission circuit according to the second embodiment is used. FIG. 11 is a third diagram for illustrating a signal transmission method when the signal transmission circuit according to the second embodiment is used.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

[Basic configuration of signal transmission circuit]
FIG. 1 is an overall block diagram of a motor drive system 100 to which a signal transmission device 200 including a signal transmission circuit according to the present embodiment is applied. The motor drive system 100 is used for home appliances, electric vehicles, and the like, for example. The motor drive system 100 is an example of an electric device to which the signal transmission circuit of the present embodiment is applied. If the application requires an analog signal to be transmitted while being insulated, the motor drive system 100 can be applied to other than the motor drive system. The signal transmission circuit can also be applied.

  Referring to FIG. 1, motor drive system 100 includes a power source 110, a power conversion device 120, a motor 130, a signal transmission device 200, and a control device 300.

  The power source 110 is composed of an AC power source such as a commercial power source or a DC power source such as a battery.

  The power conversion device 120 is typically configured to include an inverter or a converter having a power switching element, and converts the power supplied from the power supply 110 to drive the motor 130.

  Control device 300 has a function of generating a drive signal for driving motor 130 and detecting an abnormality in power conversion device 120 and motor 130. Control device 300 transmits the drive signal to power conversion device 120 through signal transmission device 200 and receives a signal indicating the state of power conversion device 120 and / or motor 130.

  The signal transmission device 200 includes a drive signal transmission circuit 210 and a temperature monitor circuit 220. The drive signal transmission circuit 210 receives a gate signal (digital signal) for driving the switching element, which is generated by, for example, PWM (Pulse Width Modulation) control in the control device 300, and converts the received gate signal into a power conversion device. 120 is output.

  The temperature monitor circuit 220 receives an analog signal indicating temperature from the temperature sensor 125 provided in the power conversion device 120 and outputs a signal corresponding to the received analog signal to the control device 300.

  In the motor drive system as shown in FIG. 1, there is an electrical connection between the motor drive unit (power conversion device 120 and motor 130) that uses a relatively high voltage and the control device 300 that uses a relatively low voltage. It is desirable to perform signal transmission in an insulated state. Therefore, in the drive signal transmission circuit 210 and the temperature monitor circuit 220 included in the signal transmission device 200, it may be necessary to electrically insulate the reception side and the transmission side.

  As a technique for transmitting a signal while being electrically insulated, it is known to use a pulse transformer or a photocoupler. In this case, generally, a signal is transmitted by a pulsed digital signal.

  As described above, since the temperature monitor circuit 220 receives an analog signal from the temperature sensor 125, in the case of signal transmission using a pulse transformer, a photocoupler, or the like, the received analog signal and a predetermined reference wave In some cases, a method of generating a duty signal based on the comparison and digitally transmitting the duty signal may be used.

  FIG. 2 is a functional block diagram for explaining the details of the temperature monitor circuit 220 in FIG. 1, which is an example of the signal transmission circuit of the present embodiment.

  Referring to FIG. 2, temperature monitor circuit 220 includes comparison unit 221, reference wave generation unit 222, pulse generation unit 223, excitation circuits 224 and 226, transmission units 225 and 227, and latch circuit 228. Including.

  Comparison unit 221 receives analog signal TEMP indicating the temperature of power conversion device 120 from temperature sensor 125 in FIG. Further, the comparison unit 221 receives the reference wave CR generated by the reference wave generation unit 222.

  The reference wave CR generated by the reference wave generator 222 is, for example, a triangular wave voltage signal having a predetermined period and amplitude, as will be described later with reference to FIG. The reference wave CR oscillates between the highest voltage VH and the lowest voltage VL, for example. The maximum voltage VH and the minimum voltage VL are set according to a voltage corresponding to the rated range of the analog signal to be compared in the comparison unit 221.

  The comparison unit 221 compares the received temperature signal TEMP with the reference wave CR, and outputs the comparison result CMP to the pulse generation unit 223.

  Based on the comparison result CMP from the comparison unit 221, the pulse generation unit 223 generates a pulse signal for generating a duty signal corresponding to the analog signal. More specifically, the drive signal PLS_A for generating the rise of the duty signal and the drive signal PLS_B for generating the fall of the duty signal are generated. The pulse generator 223 outputs the generated pulse signals PLS_A and PLS_B to the excitation circuits 224 and 226, respectively.

  The excitation circuits 224 and 226 are circuits for exciting the pulse transformers included in the transmission units 225 and 227 based on the pulse signals PLS_A and PLS_B, respectively. In the transmission units 225 and 227, a pulse signal can be transmitted by a pulse transformer while electrically insulating the input side and the output side.

  Note that the transmission unit may have a configuration other than the pulse transformer as long as it can transmit the pulse signal while being electrically insulated. For example, the transmission unit can be configured using a photocoupler. In that case, the excitation circuit may be omitted, or an amplifier circuit or the like may be provided instead of the excitation circuit.

  The pulse signal transmitted to the output side of the transmission units 225 and 227 is output to the latch circuit 228.

  Latch circuit 228 is typically formed of a flip-flop. A set input (S) of latch circuit 228 receives pulse signal PLS_A transmitted by transmission unit 225. The reset input (R) of the latch circuit 228 receives the pulse signal PLS_B transmitted by the transmission unit 227.

  Latch circuit 228 sets and holds output signal SIG output from output (Q) at a logic high state at the rising edge of the pulse received at set input (S). On the other hand, the latch circuit 228 sets and holds the output signal SIG output from the output (Q) at the logic low state at the rising edge of the pulse received at the reset input (R).

  The latch circuit 228 outputs the output signal SIG generated based on the pulse signals PLS_A and PLS_B to the control device 300.

  In this way, the temperature monitor circuit 220 converts the analog signal TEMP received from the temperature sensor 125 into a digital duty signal while being electrically insulated, and transmits it to the control device 300.

The signal transmission circuit described with reference to FIG. 2 may be configured as an integrated circuit.
[Embodiment 1]
FIG. 3 is a time chart for explaining a signal transmission method generally performed in the signal transmission circuit as shown in FIG. 3 and the subsequent FIGS. 4 to 11, time is shown on the horizontal axis, the voltage of the analog signal to be transmitted with the reference wave, and the pulse signal PLS_A generated by the pulse generator 223 on the vertical axis. PLS_B and the output signal SIG of the latch circuit 228) are shown.

  Referring to FIGS. 2 and 3, the waveform W <b> 10 in the uppermost diagram in FIG. 3 is a reference wave CR generated by the reference wave generator 222. In the present embodiment, the reference wave CR is described as an example of a triangular wave whose amplitude increases or decreases in a predetermined cycle between the highest voltage VH and the lowest voltage VL, but as another example of the reference wave CR, For example, it is possible to use a sine wave or a saw wave.

  A waveform W11 is an analog signal to be transmitted, and in the example of the temperature monitor circuit of FIG. 2, is the temperature TEMP of the power converter 120 (FIG. 1) detected by the temperature sensor 125 (FIG. 1).

  As described above, the maximum voltage VH and the minimum voltage VL of the reference wave CR are determined based on the rated operating voltage range of the analog signal to be transmitted. Therefore, in a normal case, the detected temperature TEMP varies between the highest voltage VH and the lowest voltage VL of the reference wave CR.

  When the reference wave CR (W10) increases from the lowest voltage VL to the highest voltage VH and coincides with the temperature TEMP (W11) (time t11, t13, t15 in FIG. 3), the pulse generator 223 A pulse signal PLS_A is generated.

  When the pulse signal PLS_A output from the pulse generator 223 is transmitted to the latch circuit 228 via the transmitter 225, the output signal SIG is set to logic high (ON) in the latch circuit 228.

  On the other hand, when the reference wave CR (W10) coincides with the temperature TEMP (W11) while decreasing from the highest voltage VH to the lowest voltage VL (time t12, t14, t16 in FIG. 3), the pulse generator 223 A pulse signal PLS_B is generated.

  When the pulse signal PLS_B output from the pulse generation unit 223 is transmitted to the latch circuit 228 via the transmission unit 227, the output signal SIG is set to logic low (OFF) in the latch circuit 228.

  In this way, by comparing the reference wave CR with the analog signal to be transmitted, the output signal SIG whose logical high duration changes according to the magnitude of the analog signal is generated. That is, the output signal SIG is a duty signal that is in a logic high state for a time during which the voltage of the reference wave CR is larger than the voltage of the analog signal to be transmitted, and the duty decreases as the voltage of the analog signal increases. Conversely, the duty increases as the voltage of the analog signal decreases. Note that the magnitude relationship between the voltages of the analog signals and the magnitude relationship between the temperatures TEMP depend on the characteristics of the temperature sensor used. In other words, both the case where the voltage increases as the temperature increases and the case where the voltage increases as the temperature decreases can be appropriately adapted to the characteristics of the temperature sensor used.

  Control device 300 can recognize temperature TEMP by detecting the duty of output signal SIG from temperature monitor circuit 220.

  In such a signal transmission method, a case is considered in which, for example, an abnormality occurs in which an analog signal transmission path is in an open state due to a temperature sensor failure, wiring breakage, or the like. In general, when a sensor signal is captured, a voltage is supplied from a device on the signal capturing side. Therefore, when the transmission path is opened, the input voltage is a reference wave CR as shown by a waveform W21 in FIG. It can be in a state larger than the fluctuation range.

  When the input signal changes at time t24 when the transmission path is in the open state, the pulse signal PLS_B is output from the pulse generator 223 because it intersects the reference wave CR at the point P2.

  At this time, when the pulse signal PLS_B is normally transmitted to the latch circuit 228, the output signal SIG becomes logic low (OFF), that is, the duty is 0%, as shown by the broken line waveform W23 in FIG. The actual input voltage is appropriately represented.

  However, for example, when the transmission failure of the pulse signal PLS_B occurs due to the influence of noise or the like, the output signal SIG is not reset by the latch circuit 228. After the occurrence of an abnormality, a state in which the reference wave CR and the input signal voltage do not coincide with each other does not occur, and thus the output signal SIG continues to be in a logic high (ON) state, that is, a duty 100% state (FIG. 4). Middle waveform W22). This indicates a state in which the input voltage is equal to or lower than the minimum voltage VL, and a tendency opposite to the actual input voltage state is shown.

  In the case where the input signal is normal and a pulse signal transmission failure occurs accidentally, the output signal SIG may temporarily indicate an inaccurate state. However, in this case, the output signal SIG is returned to a normal state by the pulse signal of the next cycle of the reference wave CR.

  Although not shown, when the analog signal transmission path is short-circuited and closed, the input voltage becomes smaller than the minimum voltage VL of the reference wave CR. When abnormalities that are not transmitted occur at the same time, as in the case of FIG. 4, an output signal SIG that shows a tendency opposite to the actual input voltage may be output to the control device 300.

  In this way, when a transmission path abnormality and a pulse signal transmission failure occur at the same time, the temperature state detected by the control device 300 is greatly different from the actual state, which causes a control problem. There is a risk that.

  Therefore, in the first embodiment of the present invention, an additional pulse signal (hereinafter also referred to as “additional pulse”) is output at the switching timing of the increase / decrease of the amplitude of the reference wave CR, thereby transmitting the transmission path. This improves the reliability of signal transmission in the case where the abnormality of the pulse signal and the poor transmission of the pulse signal occur simultaneously.

  FIG. 5 is a time chart for explaining the signal transmission method according to the first embodiment. Hereinafter, FIG. 5 will be described in comparison with FIG. 3 described above.

  Referring to FIGS. 3 and 5, in FIG. 5, when the reference wave CR and the analog signal (W31) coincide with each other while the voltage of the reference wave CR (W30) is increasing (time t31, t35, t39 in FIG. 5). ) When the pulse signal PLS_A is generated and the reference wave CR and the analog signal coincide with each other while the voltage of the reference wave CR is decreasing (time t33, t37, t41 in FIG. 5), the pulse signal PLS_B is output. This is the same as the case of 3.

  In FIG. 5, in addition to the above timing, when the voltage amplitude of the reference wave CR is switched from increase to decrease (time t32, t36, t40 in FIG. 5), the pulse generator 223 outputs a pulse as an additional pulse. A signal PLS_A is additionally output. When the voltage amplitude of the reference wave CR is switched from decrease to increase (time t34, t38 in FIG. 5), the pulse signal PLS_B is additionally output from the pulse generator 223 as an additional pulse.

  For example, if a transmission failure of the pulse signal PLS_A occurs at time t35 in FIG. 5, the output signal SIG is not changed to logic high at this time, so the method of the first embodiment as shown in FIG. 3 is applied. If not, the output signal SIG remains in the logic low state until time t39, which is the output timing of the pulse signal PLS_A of the next cycle. Therefore, in one cycle from time t34 to t38, the duty of the output signal SIG is 0%. Therefore, in the control device 300, the voltage of the analog signal is equal to the maximum voltage VH, that is, can be detected by the temperature sensor 125. Recognized as the maximum temperature.

  On the other hand, when the technique of the first embodiment is applied, an additional pulse of the pulse signal PLS_A is output at time t36 within the same cycle of the reference wave CR even when a transmission failure of the pulse signal PLS_A occurs at time t35. Is done. Thus, in one cycle from time t34 to time t38, the output signal SIG becomes logic high between time t36 and time t37, and the duty becomes larger than 0%.

  As described above, when the input analog signal fluctuates in the normal range, even if a temporary transmission failure of the pulse signal occurs, the state of the output signal SIG is set to a normal state within the same cycle of the reference wave CR. Can be returned. Therefore, even when a pulse signal transmission failure occurs, the error amount of the transmitted signal can be reduced.

  Next, a case where an abnormality in an analog signal transmission path and a pulse signal transmission failure occur in the first embodiment will be described with reference to FIGS. FIG. 6 shows a case where the analog signal transmission path is in an open state, and FIG. 7 shows a case where the analog signal transmission path is in a closed state.

  First, referring to FIG. 6, similarly to the description in FIG. 4, the analog signal transmission path is opened at time t57 (waveform W51 in FIG. 6), and the pulse output from pulse generator 223 at that time When a transmission failure of the signal PLS_B occurs, the output signal SIG cannot be set to logic low, and the output signal SIG remains in a logic high state.

  In the case of FIG. 4, since no pulse signal is output thereafter, the output signal SIG continues to be in a logic high state. However, in FIG. 6 of the first embodiment, at time t58 when the voltage amplitude of the reference wave CR is next switched from decrease to increase, an additional pulse of the pulse signal PLS_B is output from the pulse generation unit 223, thereby outputting Signal SIG returns to a logic low indicating the correct state.

  In the first embodiment, when the input voltage exceeds the maximum voltage VH of the reference wave CR, the pulse generator 223 further stops outputting the additional pulse of the pulse signal PLS_A (in FIG. 6). T59). This is to prevent the logical state of the output signal SIG from being unnecessarily switched by both the pulse signal PLS_A and the pulse signal PLS_B.

  More specifically, when the output of the additional pulse of the pulse signal PLS_A is not stopped as described above, the output signal SIG is switched to logic high by the additional pulse of the pulse signal PLS_A, and the additional pulse of the pulse signal PLS_B As a result, the output signal SIG is switched to logic low, and as a result, the output signal SIG having a duty of 50% is output. Therefore, when the duty in which the input voltage exceeds the maximum voltage VH of the reference wave CR is to be 0%, only the additional pulse of the pulse signal that makes the output signal SIG logically low is output.

  Next, referring to FIG. 7, when the transmission path of the analog signal is in a closed state and a transmission failure of pulse signal PLS_A occurs at that time (time t65 in FIG. 7), the output signal SIG is logically normal. Although it should be high, it remains a logic low due to poor transmission of the pulse signal PLS_A. However, by applying the first embodiment, an additional pulse of the pulse signal PLS_A is output from the pulse generation unit 223 at time t66, which is the timing at which the reference wave CR is next switched from increase to decrease, and the output signal SIG switches to a logic high state indicating the correct state.

  Further, since the input voltage is lower than the minimum voltage VL of the reference wave CR, the pulse generator 223 stops outputting the additional pulse of the pulse signal PLS_B (time t67, t69).

  As described above, by applying the first embodiment, the reliability of a signal to be transmitted is improved when an analog signal transmission path abnormality and a pulse signal transmission failure occur simultaneously during system operation. Can do.

  Further, when the method of the first embodiment is not applied, if an abnormality has already occurred in the analog signal transmission path at the timing when the system is first activated, neither of the pulse signals PLS_A and PLS_B is output. The signal SIG becomes indefinite and remains in the default state when the system is started.

  For example, as shown in FIG. 8, when the system is started at time t70, if the analog signal (W71) is already lower than the minimum voltage VL of the reference wave CR (W70), the default state of the output signal SIG is logic. When low, the duty of the output signal SIG should originally be 100% (logic high), but remains in the default logic low state.

  In such a state, when the method of the first embodiment is not applied, the logic low state continues, and the actual input voltage state and the output signal SIG state do not match.

  When the method of the first embodiment is applied, the input voltage is lower than the minimum voltage VL of the reference wave CR, and therefore, the additional pulse of the pulse signal PLS_A is changed at the timing when the voltage amplitude of the reference wave CR is switched from increase to decrease. Is output (time t71, t73, t75 in FIG. 8). As a result, the output signal SIG is switched to a logic high state indicating a correct state.

  As described above, in the signal transmission circuit according to the first embodiment, the additional pulse is additionally output at the timing when the increase / decrease in the amplitude of the reference wave is switched, and the input signal is outside the fluctuation range of the amplitude of the reference wave. In this case, the output of one of the corresponding additional pulses is stopped depending on whether the amplitude exceeds the maximum value or below the minimum value. As a result, it is possible to improve the signal transmission accuracy when a transmission failure of the pulse signal and / or an abnormality in the transmission path of the analog signal to be transmitted occurs.

[Embodiment 2]
In the second embodiment, one or more additional pulses (hereinafter also referred to as “backup pulses”) are continuously generated at the timing of outputting the pulse signal in order to reduce the influence due to the temporary transmission failure of the pulse signal. A signal transmission method for outputting the signal will be described.

  FIG. 9 is a time chart for illustrating the signal transmission method according to the second embodiment. Referring to FIG. 9, in the second embodiment, a plurality of pulse signals PLS_A and PLS_B are output from pulse generation unit 223 at the time when voltage (W80) of reference wave CR matches the voltage (W81) of the analog signal. Is output. As a result, even when a temporary transmission failure of the pulse signal occurs, the output signal SIG can be returned to the correct state by the backup pulse continuously output thereafter.

  More specifically, for example, even when a transmission failure of the pulse signal PLS_A output at time t83 in FIG. 9 occurs, the output signal SIG is in a correct logic high state by the backup pulse output at time t84 immediately after. Can be.

  On the other hand, the following problem may occur in the method of compensating for the transmission failure of the pulse signal using such a backup pulse.

  For example, as shown in FIG. 10, when the voltage of the input analog signal is close to the maximum voltage VH of the reference wave CR, the period from the output of the pulse signal PLS_A to the output of the pulse signal PLS_B is very long Becomes shorter. Then, the output timing of the pulse signal PLS_B arrives while the backup pulse of the pulse signal PLS_A is being output. Then, the output signal SIG is switched to logic low by the backup pulse of the pulse signal PLS_B after the completion of the output of the backup pulse of the pulse signal PLS_A.

  That is, originally, the output signal SIG should be logically high only from time t91 to time t92, but the logical state fluctuates depending on the state of the backup pulse between time t92 and time t93. As a result, the duty of the output signal SIG may become inaccurate.

  Although not shown, the same applies when the voltage of the analog signal is close to the minimum voltage VL of the reference wave. In this case, the period from the output of the pulse signal PLS_B to the output of the pulse signal PLS_A is shortened. The timing at which the output signal SIG becomes logic high is affected.

  In order to cope with such a state, in the second embodiment, as shown in FIG. 11, a masking process of a backup pulse is further executed in accordance with the increase / decrease state of the voltage amplitude of the reference wave CR. More specifically, when the voltage amplitude of the reference wave CR is increased, mask processing is performed so that the backup pulse of the pulse signal PLS_B is not output, and when the voltage amplitude is decreased, the backup of the pulse signal PLS_A is performed. Mask processing is performed so that no pulse is output.

  FIG. 11 is a time chart when the mask processing function is added to the case shown in FIG. At time t1, pulse signal PLS_A is output, and output signal SIG is switched to logic high. After that, a backup pulse of the pulse signal PLS_A should be output subsequently, but since the voltage amplitude of the reference wave CR (W100) begins to decrease, masking of the backup pulse of the pulse signal PLS_A is performed. As a result, the output of the backup pulse of the pulse signal PLS_A is stopped.

  After that, at time t2, the pulse signal PLS_B and subsequently the backup pulse of the pulse signal PLS_B are output. As a result, the duty of the output signal SIG becomes correct.

  In the state of FIG. 11, if a transmission failure of the pulse signal PLS_A occurs, the output signal SIG may not be switched to logic high, and the duty may become 0%. However, when the backup pulse is not output by mask processing in this way, the voltage of the analog signal is originally close to the highest voltage of the reference wave CR, that is, the duty is close to 0%. The influence due to the transmission failure of the signal PLS_A is relatively small.

  As described above, in the signal transmission circuit that transmits the analog signal while being electrically insulated as shown in FIG. 2, the pulse signal is output together with one or more continuous backup pulses, and the reference wave is increased or decreased. By appropriately performing the backup pulse masking process according to the above, it is possible to reduce the influence of the defective transmission of the pulse signal and improve the signal transmission accuracy of the output signal.

  The second embodiment may be used alone or in combination with the first embodiment.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 100 Motor drive system, 110 Power supply, 120 Power converter, 125 Temperature sensor, 130 Motor, 200 Signal transmission apparatus, 210 Drive signal transmission circuit, 220 Temperature monitor circuit, 221 Comparison part, 222 Reference wave generation part, 223 Pulse generation part 224, 226 Excitation circuit, 225, 227 Transmitter, 228 Latch circuit, 300 Control device.

Claims (12)

A signal transmission circuit for transmitting an analog signal while being electrically insulated,
A pulse generator for generating and outputting first and second pulses based on a comparison between the analog signal and a predetermined reference wave;
First and second transmission units for transmitting the generated first and second pulses while being electrically insulated;
The output signal is set on according to the first pulse transmitted by the first transmission unit, and the output signal is reset off according to the second pulse transmitted by the second transmission unit. A latch circuit configured to output the analog signal as a duty,
The signal generation circuit, wherein the pulse generation unit outputs an additional pulse for the first and second pulses when an increase or decrease in the amplitude of the reference wave is switched.   The pulse generation unit generates the first pulse when the amplitude of the reference wave coincides with the magnitude of the analog signal while the amplitude of the reference wave is increasing, and the amplitude of the reference wave is 2. The signal transmission circuit according to claim 1, wherein the second pulse is generated when the amplitude of the reference wave and the magnitude of the analog signal coincide with each other while decreasing.   The pulse generator outputs an additional pulse for the first pulse when the amplitude of the reference wave is switched from increase to decrease, and when the amplitude of the reference wave is switched from decrease to increase, The signal transmission circuit according to claim 2, wherein an additional pulse for the second pulse is output. The amplitude of the reference wave increases or decreases within a predetermined range determined by an upper limit value and a lower limit value,
When the amplitude of the reference wave reaches the upper limit value, the amplitude of the reference wave can be switched from increase to decrease, and when the amplitude of the reference wave reaches the lower limit value, the amplitude of the reference wave becomes The signal transmission circuit according to claim 3, wherein the signal transmission circuit can be switched from decrease to increase.   The pulse generation unit outputs an additional pulse for the first pulse even when the amplitude of the reference wave is switched from increase to decrease when the magnitude of the analog signal exceeds the upper limit value. The signal transmission circuit according to claim 4, which is not performed.   When the magnitude of the analog signal falls below the lower limit, the pulse generator outputs an additional pulse for the second pulse even if the amplitude of the reference wave is switched from decrease to increase. The signal transmission circuit according to claim 4 or 5, which is not performed.   The signal transmission circuit according to claim 1, wherein each of the first and second transmission units includes a transformer or a photocoupler.   The signal transmission circuit according to claim 1, wherein the pulse generation unit outputs a plurality of continuous pulses as the first and second pulses.   The pulse generator stops outputting the first pulse while the amplitude of the reference wave is decreasing, and stops outputting the second pulse while the amplitude of the reference wave is increasing. The signal transmission circuit according to claim 8.   An integrated circuit in which the signal transmission circuit according to claim 1 is integrated.   An electric device comprising the signal transmission circuit according to claim 1. A signal transmission circuit for transmitting an analog signal while being electrically insulated,
A pulse generator for generating and outputting first and second pulses based on a comparison between the analog signal and a predetermined reference wave;
First and second transmission units for transmitting the generated first and second pulses while being electrically insulated;
The output signal is set on according to the first pulse transmitted by the first transmission unit, and the output signal is reset off according to the second pulse transmitted by the second transmission unit. A latch circuit configured to output the analog signal as a duty,
The pulse generator outputs a plurality of continuous pulses as the first and second pulses,
The pulse generator stops outputting the first pulse while the amplitude of the reference wave is decreasing, and stops outputting the second pulse while the amplitude of the reference wave is increasing. A signal transmission circuit.

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