JP6513927B2 - Oscillator and calibration method therefor - Google Patents

Description

  The present invention relates to an oscillator and a calibration method thereof.

  2. Description of the Related Art In recent years, in base stations of mobile phones and transmission devices that require the Stratum 3 specification, an oscillator with a higher degree of frequency stability (for example, ± 0.28 ppm or less for Stratum 3) is required. The required level of frequency stability is further increased, and in some cases, the same degree of stability as that of an oven controlled crystal oscillator (OCXO) may be required.

The temperature compensated crystal oscillator used as the reference clock source in these applications controls the temperature characteristic of the crystal oscillator or the piezoelectric oscillator by the control signal of the voltage controlled oscillator to control the crystal oscillation frequency with respect to temperature. Make the change smaller. For example, the temperature characteristic of a crystal oscillator (AT cut) made of crystal cut at a cutting angle is approximated by a cubic function, and a control signal that cancels the temperature characteristic is generated to perform temperature compensation. In addition, frequency control (AFC: Auto Frequency Control) may be performed to adjust the offset frequency and the aging of the temperature characteristic. In this case, generally, the AFC control signal is externally input, and the input voltage thereof does not depend on temperature.
Patent Document 1 International Publication No. 2011/077705

  Generally, temperature compensation adjustment is performed by setting the AFC input to zero. After that, AFC is performed to adjust the offset frequency. If the offset frequency generated by the AFC is constant regardless of the temperature, the temperature compensation accuracy does not deteriorate at the time of AFC. However, in practice, since the equivalent capacitance of the oscillator varies with temperature and the oscillator sensitivity has temperature characteristics, the temperature compensation accuracy at the time of AFC deteriorates. Since the temperature compensation is realized by giving temperature characteristics to the equivalent capacitance of the oscillator, it is difficult to prevent the temperature compensation accuracy from deteriorating at the time of AFC.

  In a first aspect of the present invention, a quartz oscillator, a first control terminal and a second control terminal connected to the quartz oscillator, and a predetermined temperature are detected to generate a first temperature signal. (1) A temperature detection circuit, a temperature compensation signal generation unit that generates a first control signal that is input to the first control terminal and controls the oscillation frequency of the crystal oscillator based on the first temperature signal, and the oscillation frequency of the crystal oscillator And a variable gain amplifier that is input to the second control terminal and generates a second control signal that controls the oscillation frequency of the crystal oscillator based on a frequency control signal that controls the second temperature, and detects a predetermined temperature, An oscillator is provided that includes a second temperature detection circuit that generates a signal, and a gain adjustment signal generation unit that generates a gain adjustment signal that controls the gain of the variable gain amplifier based on the second temperature signal.

  In the second aspect of the present invention, at each temperature, a first control signal is input such that a predetermined constant value is input as the frequency control signal, and the oscillation frequency of the crystal oscillator matches the predetermined oscillation frequency. In the state of being input to the first control terminal, a gain adjustment signal that corresponds to the frequency control signal and in which the oscillation frequency of the crystal unit coincides with the target oscillation frequency is input to the variable gain amplifier, and the gain at each temperature An oscillator that measures the gain adjustment signal output from the adjustment signal generation unit and adjusts the set value of the gain adjustment signal generation unit so that the output gain adjustment signal and the input gain adjustment signal match at each temperature Provide a way to adjust the

  Note that the above summary of the invention does not enumerate all the necessary features of the present invention. In addition, a subcombination of these feature groups can also be an invention.

The structural example of the conventional oscillator 100 is shown. 2 shows an exemplary configuration of an approximate n-th order function generation circuit 20. 2 shows an exemplary configuration of a first gain variable circuit 30. FIG. The ideal value of the temperature characteristic of the frequency at the time of offset frequency adjustment is shown. The actual value of the temperature characteristic of the frequency at the time of offset frequency adjustment is shown. The relationship between the oscillation frequency f of the oscillator 100 and the equivalent capacitance C _CL is shown. 7 shows an exemplary configuration of an oscillator 200. A specific configuration example of the oscillator 200 is shown. 7 shows an exemplary configuration of a second gain variable circuit 60. 7 shows an exemplary configuration of a gain adjustment signal generation unit 80 and a second temperature detection circuit 90. 7 shows an exemplary configuration of a gain adjustment signal generation unit 80 and a second temperature detection circuit 90. 7 shows an exemplary configuration of an oscillator 300. The structural example of the 1st gain variable circuit 30, the 2nd gain variable circuit 60, and the gain amplifier circuit 110 is shown. An exemplary configuration of the oscillator 400 is shown. 7 shows an exemplary configuration of a gain adjustment signal generation unit 120 and a second temperature detection circuit 90. An example of a temperature compensation adjustment sequence is shown. An example of a gain temperature characteristic adjustment sequence is shown.

  Hereinafter, the present invention will be described through the embodiments of the invention, but the following embodiments do not limit the invention according to the claims. Moreover, not all combinations of features described in the embodiments are essential to the solution of the invention.

  FIG. 1 shows a configuration example of a conventional oscillator 100. As shown in FIG. The oscillator 100 includes an oscillating unit 10, an approximate nth-order function generating circuit 20, and a gain variable circuit 30.

  The oscillating unit 10 oscillates at a frequency according to the first control signal V1 and the second control signal V2 input from the approximate n-th order function generation circuit 20 and the gain variable circuit 30. The oscillation unit 10 has a crystal oscillator SS, a feedback resistor R, an amplifier A, a first control element 11, a second control element 12, a first control terminal 13 and a second control terminal 14.

  The approximate n-th order function generation circuit 20 outputs the first control signal V1 to the first control terminal 13 in order to make the temperature characteristic of the oscillating unit 10 constant. In general, the frequency of the quartz oscillator SS fluctuates according to the change of the environmental temperature. For example, the frequency of the quartz oscillator SS deviates from the predetermined reference frequency by the first frequency offset due to the change of the environmental temperature. In this case, the first control signal V1 is determined to compensate for the first frequency offset.

  For example, the approximate nth-order function generation circuit 20 determines a first correction value according to the environmental temperature as the first control signal V1. Here, the first correction value is a correction value that makes the temperature characteristic of the oscillation unit 10 to which the second control signal V2 is input constant in order to operate with the first frequency offset. The first correction value may be measured at each predetermined temperature. Although the environmental temperature in this example is the temperature of the approximate n-th order function generation circuit 20, it may be any environmental temperature inside the oscillator 100 or the temperature outside the oscillator 100.

  In the present specification, the “temperature characteristic” indicates the oscillation frequency characteristic of the oscillation unit 10 with respect to a change in temperature. Further, "the temperature characteristic is constant" indicates that the oscillation frequency is substantially constant regardless of the temperature change. Further, “substantially constant” may indicate that the fluctuation of the oscillation frequency of the oscillation unit 10 is reduced by about 90% as compared with that before the correction by the approximate nth-order function generation circuit 20.

The first gain variable circuit 30 adjusts the oscillation frequency of the oscillation unit 10 according to the input frequency control signal. The frequency control signal is a signal corresponding to the target oscillation frequency of the oscillation unit 10. For example, the frequency control signal of the present embodiment, the input voltage V _in input from the outside. First gain variable circuit 30 generates a second control signal V2 obtained by amplifying the input voltage _{V in.} The second control signal V 2 is input to the second control element 12 via the second control terminal 14 to control the oscillation frequency of the oscillating unit 10.

  The crystal oscillator SS vibrates at an oscillation frequency corresponding to the crystal parameter and the oscillator parameter. The input terminal Va and the output terminal Vb of the crystal unit SS are connected to the first control element 11 and the second control element 12, respectively.

  The feedback resistor R is a resistor connected in parallel to the crystal unit SS. The feedback resistor R feeds a signal back to the input terminal Va of the crystal unit SS from the output terminal Vb side of the crystal unit SS to determine the DC operating point of the input and output of the crystal unit SS.

  The amplifier A is connected in parallel with the crystal unit SS to generate a negative resistance to continue the oscillation of the crystal unit SS. For example, the amplifier A is configured by a CMOS inverter.

  The first control element 11 controls the oscillation frequency of the crystal oscillator SS based on the first control signal V1 output from the approximate n-th order function generation circuit 20. The first control element 11 includes a first variable capacitance element MA1 and a first variable capacitance element MB1 whose capacitance changes in accordance with the input voltage.

  Each of the first variable capacitance elements (MA1, MB1) is formed of a MOS transistor. In the first variable capacitance element MA1, the gate terminal is connected to the approximate n-th order function generation circuit 20 via the first control terminal 13, and the source terminal is connected to the input terminal Va of the crystal unit SS. In the first variable capacitance element MB1, the gate terminal is connected to the approximate n-th order function generation circuit 20 via the first control terminal 13, and the source terminal is connected to the output terminal Vb of the crystal unit SS. The first control signal V1 from the approximate n-th order function generation circuit 20 is input to the gate terminal of the first variable capacitance element (MA1, MB1).

  The second control element 12 controls the oscillation frequency of the crystal oscillator SS based on the second control signal V2 output from the first gain variable circuit 30. The second control element 12 includes a second variable capacitance element MA2 and a second variable capacitance element MB2 whose capacitances change in accordance with the input voltage.

  Each of the second variable capacitance elements (MA2, MB2) is formed of a MOS transistor. In the second variable capacitance element MA2, the gate terminal is connected to the first gain variable circuit 30 via the second control terminal 14, and the source terminal is connected to the input terminal Va of the crystal unit SS. In the second variable capacitance element MB2, the gate terminal is connected to the first gain variable circuit 30 via the second control terminal 14, and the source terminal is connected to the output terminal Vb of the crystal unit SS. The second control signal V2 from the first gain variable circuit 30 is input to the gate terminal of the second variable capacitance element (MA2, MB2).

  A reference voltage (for example, a ground potential) is applied to the bulk of the MOS transistor constituting the variable capacitance element (MA1, MA2, MB1, MB2). The drain terminals of the MOS transistors constituting the variable capacitance elements (MA1, MA2, MB1, MB2) of this example do not have connection targets, but the drain terminals may be connected to the source terminals.

  In addition, the oscillation part 10 of this example adjusted the oscillation frequency of the crystal oscillator SS by providing four variable capacitance elements (MA1, MA2, MB1, MB2). However, the oscillation unit 10 can adjust the oscillation frequency of the crystal oscillator SS if it has at least one variable capacitance element. For example, the oscillation unit 10 has two variable capacitance elements (MA1, MA2) connected to the input terminal Va, but does not have two variable capacitance elements (MB1, MB2) connected to the output terminal Vb. It may be. Furthermore, two variable capacitive elements (MA1, MA2) and (MB1, MB2) may be shared, and a control signal obtained by adding the first control signal V1 and the second control signal V2 may be used as an input.

  FIG. 2 shows a configuration example of the approximate n-th order function generation circuit 20. The approximate nth-order function generation circuit 20 includes a first temperature detection circuit 50 and a temperature compensation signal generation unit 40.

The first temperature detection circuit 50 detects an environmental temperature of a predetermined portion of the oscillator 100. The environmental temperature in this example is the temperature of the approximate nth-order function generation circuit 20. For example, the first temperature detection circuit 50 generates a first temperature sensor voltage V _tsens as a first temperature signal. The first temperature sensor voltage V _tsens is input to the temperature compensation signal generation unit 40.

The temperature compensation signal generation unit 40 generates a first control signal V1 based on the input first temperature sensor voltage _Vtsens . The temperature compensation signal generation unit 40 includes a function generation unit 41 and a voltage adder 42.

  The function generation unit 41 generates a plurality of functions in order to generate the first control signal V1 that causes the oscillation unit 10 to oscillate at a predetermined oscillation frequency. The function generation unit 41 includes a primary component generation circuit 41a, a secondary component generation circuit 41b, a tertiary component generation circuit 41c, a quaternary component generation circuit 41d, and a quaternary component generation circuit 41e. The function generation unit 41 does not have to include all of the primary component generation circuit 41a to the fifth component generation circuit 41e, and includes at least one of the first component generation circuit 41a to the fifth component generation circuit 41e. Just do it.

The first temperature sensor voltage V _tsens is input to each of the primary component generation circuit 41 a to the fifth order component generation circuit 41 e. The first-order component generation circuit 41a to the fifth-order component generation circuit 41e generate a voltage _obtained by _powering the first temperature sensor voltage V _tsens according to the order and _multiplying the first temperature sensor voltage V _tsens by a predetermined coefficient of positive or negative value. . Each coefficient in the primary component generating circuit 41a to the fifth component generating circuit 41e is determined by a first correction value to be generated for each temperature. The coefficients in the primary component generation circuit 41a to the primary component generation circuit 41e are set variably. Thus, the relationship between the environmental temperature detected by the first temperature detection circuit 50 and the first control signal V1 can be variably set.

  The voltage adder 42 adds the signals of the respective orders generated by the function generation unit 41. As a result, the signal output from the voltage adder 42 is the temperature-dependent first control signal V1 having an arbitrary order from the first to the fifth.

FIG. 3 shows a configuration example of the first gain variable circuit 30. As shown in FIG. The first gain variable circuit 30 includes an operational amplifier 31, a resistor 32, and a variable feedback resistor 33 to configure an inverting amplification circuit. That is, the inverting input terminal of the operational amplifier 31 is connected to one end of the resistor 32, and the variable feedback resistor 33 is connected to the inverting input terminal and the output terminal of the operational amplifier 31 in parallel with the operational amplifier 31. The first gain variable circuit 30 outputs a second control signal V 2 obtained by amplifying the input voltage V _in with an arbitrary gain to the second control terminal 14.

4 and 5 show an ideal value (FIG. 4) and an actual value (FIG. 5) of the temperature characteristic of the frequency at the time of offset frequency adjustment. The horizontal axis represents temperature, and the vertical axis represents frequency f. In this example, the reference frequency is f ₀ and the offset amount of the first frequency offset is 0. Also, let f ₁ be the frequency offset by the second frequency offset. That is, f ₀ indicates the frequency in the state where the offset is not adjusted (at the time of VAFC center). The offset refers to the amount of change from the reference frequency at the VAFC center. VAFC refers to a voltage for AFC. For example, VAFC is the input voltage V _in input to the first gain variable circuit 30.

FIG. 4 shows the temperature characteristic of the ideal frequency after offset adjustment. The oscillator 100 is adjusted by the first control signal V1 output from the approximate n-th order function generation circuit 20 so that the oscillation frequency of the oscillation unit 10 becomes constant at f ₀ regardless of the temperature. That is, the first control signal V1 is detected such that the temperature characteristic of the oscillating unit 10 becomes constant. Even if the second control signal V2 by the oscillation frequency f from the first gain variable circuit 30 is changed from f ₀ to f _1, and controls the oscillation section 10 by the first control signal V1 described above. Ideally, even when the oscillation frequency changes to f ₁ , as shown in FIG. 4, at any of the temperatures (T _a , T ₀ , T _b ), the amount of change in frequency (Δf L _a , It is preferable that ΔfL ₀ and ΔfL _b ) be equal to each other, and the temperature characteristic of the oscillation frequency of the oscillation unit 10 be constant at f ₁ .

FIG. 5 shows the temperature characteristics of the actual frequency after the offset adjustment. In fact, when the oscillation frequency f is changed from f ₀ to f ₁ , if the same first control signal V 1 as before the change of the oscillation frequency is used, the frequency at the temperature (T _a , T ₀ , T _b ) The amount of change (ΔfL _a , ΔfL ₀ , ΔfL _b ) of each other is different from each other. Therefore, frequency f after offset adjustment does not become constant frequency f ₁ . That is, even if the temperature characteristic of the frequency f is adjusted at the VAFC center, the temperature characteristic deteriorates after the offset adjustment, and the temperature characteristic of the oscillator 100 can not be accurately compensated.

FIG. 6 shows the relationship between the oscillation frequency f (vertical axis) of the oscillator 100 and the equivalent capacitance C _CL (horizontal axis). It can be seen from FIG. 6 that although the oscillation frequency f of the oscillator 100 decreases as the equivalent capacitance C _CL of the oscillator 100 increases, the slope of the decrease is not constant.

When the equivalent capacitance C _CL of the oscillator 100 is reduced by ΔCL at each frequency (f _a , f ₀ , f _b ) having different frequency offset, the oscillation frequency f of each frequency (f _a , f ₀ , f _b ) The amounts of change (ΔfL _a , ΔfL ₀ , ΔfL _b ) have mutually different values. For this reason, when the frequency offset is changed, the magnitude of the frequency compensated by the first control signal V1 fluctuates, and the temperature characteristic is compensated excessively or excessively. That is, the temperature characteristic after offset adjustment is degraded because the equivalent capacitance C _CL of the oscillator 100 is different due to the temperature characteristic of the first control signal V 1 and the oscillator sensitivity seen from the second control terminal is changed. In addition, it is also one of the causes that the sensitivity of the original oscillator 100 has temperature characteristics.

  The deterioration of the temperature characteristic as described above has less influence on a temperature compensated oscillator that requires frequency stability of about several ppm. However, for example, it is not preferable in a temperature compensated oscillator such as a mobile phone base station requiring high frequency stability, such as 0.5 ppm or less, or a transmission apparatus of Stratum 3 standard. As an example, Stratum 3 requires frequency stability within ± 0.28 ppm. Furthermore, in recent years, frequency stability comparable to OCXO may be required.

  FIG. 7 shows a configuration example of the oscillator 200. The oscillator 200 differs from the oscillator 100 in that a second gain variable circuit 60 for adjusting gain temperature characteristics is provided instead of the first gain variable circuit 30.

  The second gain variable circuit 60 compensates for the deterioration of the temperature characteristic that occurs when the oscillating unit 10 has the temperature characteristic of the sensitivity of the second control signal V2. The second gain variable circuit 60 generates a second control signal V2 based on the detected environmental temperature. For example, the second gain variable circuit 60 generates a second correction value as the second control signal V 2 and outputs the second correction value to the second control terminal 14.

The second correction value is a correction value that makes the temperature characteristic of the oscillation unit 10 to which the first control signal V1 is input constant. That is, the second correction value is a second control signal V2 that makes the temperature characteristic of the oscillating unit 10 constant while the first control signal V1 corresponding to the first correction value is input to the first control terminal 13. is there. That is, at the time of measurement at each temperature of the second correction value, the first control signal V1 corresponding to the first correction value at each temperature is input to the first control terminal 13. Specifically, the second control signal V2 is generated by amplifying the difference between the input voltage V _in and the bias voltage V _bias by the gain determined by the gain variable circuit.

  FIG. 8 shows a specific configuration example of the oscillator 200. The second gain variable circuit 60 of this example includes a variable gain amplifier (VGA) 70, a gain adjustment signal generation unit 80, and a second temperature detection circuit 90.

The second temperature detection circuit 90 detects an environmental temperature of a predetermined portion of the oscillator 200. The environmental temperature detected by the second temperature detection circuit 90 of this example is the temperature of the second gain variable circuit 60. The environmental temperature detected by the second temperature detection circuit 90 may be the same as or different from the environmental temperature detected by the first temperature detection circuit 50. For example, the second temperature detection circuit 90 generates a second temperature sensor voltage V _tsens as a second temperature signal. The second temperature sensor voltage V _tsens is input to the gain adjustment signal generation unit 80. As will be described later, by making the input voltage V _in generating the first offset frequency the same as the bias voltage V _bias , the second gain variable can be adjusted even if the gain is changed by adjusting the gain of the second gain variable circuit 60. Since the signal amplified by the circuit 60 is 0, the potential of the second control signal V2 does not change. Thus, the second gain variable circuit 60 compensates for the temperature characteristic independently of the approximate nth-order function generation circuit 20. By compensating the temperature characteristics independently, even if the second gain variable circuit 60 performs AFC after the approximate n-th order function generation circuit 20 performs temperature compensation, the temperature compensation accuracy does not easily deteriorate.

The gain adjustment signal generation unit 80 generates a gain adjustment signal based on the second temperature sensor voltage _Vtsens . Further, the gain adjustment signal generation unit 80 outputs the generated temperature dependent current to the variable gain amplifier 70. For example, the gain adjustment signal is a temperature-dependent current defined by a fifth-order function with the environmental temperature as a variable.

The variable gain amplifier 70 amplifies the input voltage V _in with a gain corresponding to the temperature dependent current from the gain adjustment signal generation unit 80. The variable gain amplifier 70 outputs the amplified signal to the second control terminal 14 as the second control signal V2.

FIG. 9 shows a configuration example of the second gain variable circuit 60. The variable gain amplifier 70 of this example amplifies and outputs the single input voltage V _in as it is (without generating a differential signal). The variable gain amplifier 70 includes a mirror circuit 73, an operational amplifier 71 and a resistor 72.

The mirror circuit 73 includes a first MOS transistor MOS1, a second MOS transistor MOS2, a first transistor Tr1, and a second transistor Tr2. The base terminal of the first transistor Tr1 input voltage V _in, the base terminal of the second transistor Tr2 bias 1 are input. The bias 1 in this example is a variable bias, and is set such that the differential input of the gain variable circuit becomes 0 when the input voltage V _in is the reference voltage.

The collector terminal and the emitter terminal of the first transistor Tr1 are connected to the drain terminal of the first MOS transistor MOS1 and the gain adjustment signal generation unit 80, respectively. The drain terminals of the first MOS transistor MOS1 and the second MOS transistor MOS2 become the reference voltage V _ref . The gate terminals of the first MOS transistor MOS1 and the second MOS transistor MOS2 are connected to the drain terminal of the first MOS transistor MOS1. This constitutes a current mirror circuit.

  The drain terminal of the second MOS transistor MOS2 is connected to the collector terminal of the second transistor Tr2 and the inverting input terminal of the operational amplifier 71. The emitter terminal of the second transistor Tr2 is connected to the gain adjustment signal generation unit 80.

The first 1MOS transistor MOS1 and first transistors Tr1, a current _{I 1} flows in accordance with the input voltage _{V in.} The first 2MOS transistor MOS2, flows current _{I 2} mirrored current _{I 1.} If the characteristics of the 1MOS transistor MOS1 and a 2MOS transistor MOS2 is the same, the current _{I 1} and the current _{I 2} are equal.

The gain adjustment signal generation unit 80 adjusts the gain of the output current I _out with respect to the input voltage V _in according to the environmental temperature. Specifically, the gain adjustment signal generation unit 80 finely adjusts the tail current output to the mirror circuit 73 according to the environmental temperature to control the gain of the mirror circuit 73.

The mirror circuit 73 generates the output current I _out with a gain corresponding to the tail current generated by the gain adjustment signal generation unit 80. The output current I _out is the difference between the current I ₂ flowing to the second MOS transistor MOS ₂ and the current I ₂ ′ flowing to the second transistor Tr ₂ . Further, the gain adjustment signal generation unit 80 adjusts the output current I _out by finely adjusting the tail current that defines the magnitude of the sum of the current I ₁ and the current I ₂ ′ according to the environmental temperature. The output current I _out is proportional to the product of the difference between the input voltage V _in and the bias voltage V _bias and the tail current.

The operational amplifier 71 amplifies the output current I _out and outputs it to the second control terminal 14. The output current I _out from the mirror circuit 73 is input to the inverting input terminal of the operational amplifier 71. The operational amplifier 71 forms an amplifier circuit with the resistor 72 connected to the output terminal and the inverting input terminal so as to be in parallel with the operational amplifier 71.

  FIG. 10 shows a configuration example of the gain adjustment signal generation unit 80. The gain adjustment signal generation unit 80 of this example includes a function generation unit 81, a voltage adder 82, and a V-I conversion circuit 83.

  The function generation unit 81 generates a multi-order function to generate the second control signal V2 that causes the oscillation unit 10 to oscillate at a predetermined oscillation frequency. The function generation unit 81 includes a primary component generation circuit 81a, a secondary component generation circuit 81b, a tertiary component generation circuit 81c, a quaternary component generation circuit 81d, and a quaternary component generation circuit 81e. The function generation unit 81 does not have to include all of the primary component generation circuit 81a to the fifth component generation circuit 81e, and at least one of the first component generation circuit 81a to the fifth component generation circuit 81e. Just do it.

The second temperature sensor voltage V _tsens detected by the second temperature detection circuit 90 is input to the primary component generation circuit 81 a to the fifth order component generation circuit _{81 e} . The primary component generation circuit 81a to the fifth component generation circuit 81e are configured to raise the input second temperature sensor voltage V _tsens according to the order and to multiply the predetermined coefficient of positive or negative value. Generate a voltage. Each coefficient in the primary component generating circuit 81a to the fifth component generating circuit 81e is determined according to the second correction value to be generated for each temperature. The respective coefficients in the primary component generation circuit 81a to the primary component generation circuit 81e are variably set. Thus, the relationship between the environmental temperature detected by the second temperature detection circuit 90 and the gain of the variable gain amplifier 70 can be variably set.

  The voltage adder 82 generates a signal obtained by adding the signals of each order generated by the function generation unit 81. Thus, the signal output from the voltage adder 82 is a temperature-dependent signal having an arbitrary order from the first to fifth orders.

  The V-I conversion circuit 83 converts the voltage added by the voltage adder 82 into a current to generate a temperature dependent current. The V-I conversion circuit 83 outputs the converted temperature-dependent current as a tail current of the mirror circuit 73 to the variable gain amplifier 70. The tail current input to variable gain amplifier 70 is dependent on the ambient temperature, and is used to compensate for the deviation of the frequency temperature characteristic that occurs during AFC operation after temperature compensation.

  FIG. 11 shows a more specific configuration example of the gain adjustment signal generation unit 80. As shown in FIG. The gain adjustment signal generation unit 80 of this example is different from the gain adjustment signal generation unit 80 described in FIG. 10 in that the function adjustment unit 84 and the storage unit 89 are included.

  The function variable unit 84 includes a plurality of volumes 1 to 5 (84a to 84e) that adjust each voltage output from the function generation unit 81. Volumes 1 to 5 (84a to 84e) are connected to respective primary component generation circuits 81a to 5th component generation circuits 81e of function generation unit 81. The volumes 1 to 5 (84a to 84e) adjust the coefficients of the respective orders in the function generated by the function generation unit 81 by adjusting the voltage values output from the function generation unit 81. Each volume 1 to 5 (84a to 84e) may be adjusted by an EEPROM (Electrical Programmable Read-Only Memory).

  The storage unit 89 stores adjustment values for adjusting the gain of the variable gain amplifier 70. The storage unit 89 is connected to the function variable unit 84. For example, the adjustment value stored in the storage unit 89 is input to each of the plurality of volumes 1 to 5 (84a to 84e). Thereby, the function variable unit 84 can adjust each voltage output from the function generation unit 81 with a coefficient based on the adjustment value stored in the storage unit 89.

  The voltage adder 82 adds the outputs from the function variable unit 84 to generate first to fifth function voltages. The voltage adder 82 includes an operational amplifier 85, resistors (86a, 86b, 86c, 86d, 86e) and a feedback resistor 86f to form a summing amplifier circuit.

  The resistors (86a-86e) are connected in series to volumes 1-5 (84a-84e) respectively. The resistors (86a to 86e) are arranged in parallel with each other and connected to the inverting input terminal of the operational amplifier 85.

  The non-inverting input terminal of the operational amplifier 85 is connected to the analog ground. Further, a feedback resistor 86 f is disposed in parallel with the operational amplifier 85 between the output terminal and the inverting input terminal of the operational amplifier 85. Thus, the voltage adder 82 adds the voltages output from the function variable unit 84 and outputs the result to the V-I conversion circuit 83.

  The V-I conversion circuit 83 converts the voltage added by the voltage adder 82 into a current and outputs the current as a tail current of the mirror circuit 73 to the variable gain amplifier 70. The V-I conversion circuit 83 includes an operational amplifier 87, a resistor 88, a third transistor Tr3 and a fourth transistor Tr4.

  The voltage added by the voltage adder 82 is input to the inverting input terminal of the operational amplifier 87. The output terminal of the operational amplifier 87 is connected to the base terminals of the third transistor Tr3 and the fourth transistor Tr4. The voltage at the collector terminal of the third transistor Tr3 is input to the non-inverting input terminal of the operational amplifier 87. Emitter terminals of the third transistor Tr3 and the fourth transistor Tr4 are connected to the ground.

The collector terminal of the third transistor Tr3 is connected to the reference voltage V _ref via the resistor 88. That is, the operational amplifier 87, the third transistor Tr3, and the resistor 88 are circuits for converting the voltage input from the voltage adder 82 into a current. On the other hand, the third transistor Tr3 and the fourth transistor Tr4 generate a mirror current obtained by mirroring the converted current, and output the mirror current to the variable gain amplifier 70.

  FIG. 12 shows a configuration example of the oscillator 300. The oscillator 300 of this example differs from the oscillator 200 in that the oscillator 300 further includes the first gain variable circuit 30 and the gain amplification circuit 110.

The gain amplification circuit 110 amplifies the input voltage V _in and outputs the amplified input voltage V _in to the first gain variable circuit 30. Further, the gain amplification circuit 110 is provided in parallel with the second gain variable circuit 60. That is, amplified signals are input to the first gain variable circuit 30 from the second gain variable circuit 60 and the gain amplifier circuit 110. A signal may be selectively input to the first gain variable circuit 30 from the second gain variable circuit 60 or the gain amplification circuit 110.

  FIG. 13 shows a configuration example of the first gain variable circuit 30, the second gain variable circuit 60, and the gain amplifier circuit 110 shown in FIG. The second gain variable circuit 60 of this example has the same configuration as the second gain variable circuit 60 shown in FIG.

The gain amplifier circuit 110 of this example includes an operational amplifier 111, a resistor 112, and a feedback resistor 113, and operates as an inverting amplifier circuit. The input voltage V _in is input to the inverting input terminal of the operational amplifier 111 via the resistor 112. The non-inverting input terminal of the operational amplifier 111 is connected to the analog ground. A feedback resistor 113 is provided in parallel with the operational amplifier 111 between the output terminal of the operational amplifier 111 and the inverting input terminal.

  The first gain variable circuit 30 is an addition circuit that adds the output of the second gain variable circuit 60 and the output of the gain amplification circuit 110. The first gain variable circuit 30 includes, in parallel, resistors 32 and 34 to which the outputs of the second gain variable circuit 60 and the gain amplifier circuit 110 are respectively input. The outputs of the second gain variable circuit 60 and the gain amplification circuit 110 combined via a resistor are input to the inverting input terminal of the operational amplifier 31.

  FIG. 14 shows a configuration example of the oscillator 400. The oscillator 400 of this example differs from the oscillator 200 shown in FIG. 8 in that a gain adjustment signal generation unit 120 is provided instead of the gain adjustment signal generation unit 80. The configuration having the same reference numeral as that of the oscillator 200 shown in FIG. 8 functions in the same manner as the oscillator 200.

The gain adjustment signal generation unit 120 generates a temperature dependent current based on the second temperature sensor voltage V _tsens generated by the second temperature detection circuit 90. Further, the gain adjustment signal generation unit 120 outputs the generated temperature dependent current to the variable gain amplifier 70. The gain adjustment signal generation unit 120 of this example generates a temperature-dependent current further based on the second control signal V2 output from the variable gain amplifier 70. Accordingly, the gain adjustment signal generation unit 120 can increase the temperature compensation accuracy of the second gain variable circuit 60.

  FIG. 15 shows a configuration example of the gain adjustment signal generation unit 120. The gain adjustment signal generation unit 120 of this example further includes a determination circuit 121 and a multiplexer 124 in addition to the configuration of the gain adjustment signal generation unit 80 shown in FIG.

  The determination circuit 121 compares the relationship between the second control signal V2 input to the gain adjustment signal generation unit 120 and a predetermined reference value. The determination circuit 121 determines whether the AFC gain should be on the + side or the − side based on the comparison result of the second control signal V2 and the reference value, and generates a determination signal. Also, the generated determination signal is input to the control terminal of the multiplexer 124. The AFC gain indicates the ratio of the second control signal V2 to the frequency control signal. The determination circuit 121 may compare the relationship between the frequency control signal and the reference value. For example, the reference value indicates analog ground.

  The storage unit 89 includes an AFC + side ROM 122 and an AFC− side ROM 123. The storage unit 89 stores a plurality of adjustment values corresponding to the determination result of the determination circuit 121. The AFC + side ROM 122 outputs the gain adjustment signal on the AFC + side to the input terminal of the multiplexer 124. The AFC-side ROM 123 also outputs the AFC-side gain adjustment signal to the input terminal of the multiplexer 124. In this example, the ROM switching has been described, but the same applies to the case where a plurality of voltage generating units (the function generating unit 81, the voltage adder 82, and the function variable unit 84 in FIG. 15) are provided and the voltage is switched by a switch or the like. The effect of

  The multiplexer 124 selects a signal to be output based on the input determination signal. The multiplexer 124 outputs one of the selected gain adjustment signals to the function variable unit 84 in accordance with the determination signal from the determination circuit 121. The gain adjustment signal may be input to each of the volumes 1 to 5 (84a to 84e). Thereby, the gains of the volumes 1 to 5 (84a to 84e) can be adjusted on the + side and the-side. Further, the gains of the set volumes 1 to 5 (84a to 84e) may be stored in the storage unit 89.

  The gain adjustment signal generation unit 120 of this example adjusts the AFC gain separately on the + side and the − side even when the AFC gain deviates on the + side and the − side with the frequency control signal 0 as the boundary. it can. Therefore, the gain adjustment signal generation unit 120 can increase the accuracy of AFC gain adjustment, and can further reduce the degradation of the temperature compensation accuracy at the time of AFC startup.

  FIG. 16 shows an example of a temperature compensation adjustment sequence for measuring the first correction value. In this example, the oscillator 200 will be described as an example.

In step S101, a predetermined fixed value is input to the second gain variable circuit 60 as a frequency control signal. When the frequency control signal of the present embodiment and the input voltage V _in, the input voltage V _in is input to the second variable gain circuit 60 is set to 0. When the input voltage V _in is 0, the oscillation frequency of the oscillation unit 10 is set to the reference frequency in the state where the offset is not adjusted (at the time of VAFC center).

  In step S102, the temperature of the oscillator 200 is set to an arbitrary temperature. The temperature set in step S102 is maintained constant until the measurement (step S104) of the temperature characteristic of the approximate n-th order function generation circuit 20 at that temperature is completed.

  In step S103, the first external control signal input to the first control terminal 13 from outside the IC is measured. The first external control signal compensates for the temperature characteristic of the oscillation frequency of the oscillator 200. For example, in the mode in which a voltage is input from the outside of the IC, an arbitrary external voltage is input to the first control terminal 13 from the outside of the IC when measuring the first correction value at each temperature. In step S103, a first external control signal in which the oscillation frequency of the oscillation unit 10 is a reference frequency is measured.

  In step S104, the first control signal V1 output from the approximate n-th order function generation circuit 20 is monitored to measure the temperature characteristic. For example, in the mode in which the voltage inside the IC is monitored, the relationship between the set value of the approximate n-order function generation circuit 20 and the first control signal V1 output from the approximate n-order function generation circuit 20 at a set temperature is monitored Do. The setting value of the approximate n-th order function generation circuit 20 indicates a coefficient in each order of the function generated by the approximate n-th order function generation circuit 20.

  In step S105, it is determined whether the temperature sweep has ended. If the temperature sweep is completed, the process proceeds to step S106. If the temperature sweep is not completed, the process returns to step S102, the next temperature is set, and steps S103 to S105 are repeated. For example, the range of the temperature sweep is determined according to the temperature range that can be detected in the oscillator 200. In addition, although the temperature compensation accuracy is improved as the temperature sweep interval is shorter, the user may arbitrarily determine according to the use environment of the oscillator 200 or the required accuracy.

  In step S106, the set value of the approximate n-th order function generation circuit 20 is calculated so as to minimize the error at each temperature. More specifically, the setting value of the approximate n-th order function generation circuit 20 is set such that the first external control signal of step S103 and the signal output from the approximate n-th order function generation circuit 20 are equal in step S104. . Note that "signals are equal" means that the compared signals are approximately equal. Further, “approximately equal” may be, for example, a range that satisfies the accuracy required by the user, and a deviation may occur in the values of the signals.

FIG. 17 shows an example of a gain temperature characteristic adjustment sequence for measuring the second correction value. In step S201, the optimum code of the approximate nth-order function generation circuit 20 is set in accordance with the temperature compensation sequence shown in FIG. Here, by setting the optimum code n-th order approximation function generation circuit 20, in a state where 0 is input to the second variable gain circuit 60 as the input voltage V _in, at each temperature, setting the first correction value Point to

  In step S202, the oscillator 200 is set to a predetermined temperature. For example, although the predetermined temperature is room temperature, it may be set to any temperature other than room temperature.

In step S203, the gain characteristic (G _ref ) of the oscillation frequency with respect to the input voltage V _in at room temperature is measured. In step S202, if you select the temperatures other than room temperature, at any selected temperature, measuring the gain characteristic of the oscillation frequency of the oscillator 10 to the input voltage V _in.

  In step S204, the temperature of the oscillator 200 is set to an arbitrary temperature. The temperature set in step S204 is kept constant until the measurement of the temperature characteristic of the gain adjustment signal generation unit 80 at that temperature (step S206) is completed.

In step S205, the voltage input to the variable gain amplifier 70 from the outside of the IC is measured. For example, in the mode for inputting the voltage from the outside of the IC, the gain characteristic of the oscillation frequency with respect to the input voltage V _in it is such that the G _ref, and inputs the gain control signal to the variable gain amplifier 70 from the gain adjusting signal generation section 80. The gain adjustment signal when the gain characteristic becomes G _ref is the compensation value of the gain adjustment signal.

  In step S206, the temperature characteristic to be compensated is measured in the mode in which the voltage inside the IC is monitored. For example, in the mode of monitoring the voltage inside the IC, the gain adjustment signal output from the gain adjustment signal generation unit 80 is measured.

  In step S207, it is determined whether the temperature sweep has ended. If the temperature sweep is completed, the process proceeds to step S208. If the temperature sweep is not completed, the process returns to step S203, the next temperature is set, and steps S203 to S207 are repeated.

  In step S208, the set value of the second gain variable circuit 60 is adjusted such that the gain adjustment signal output from the gain adjustment signal generation unit 80 matches the compensation value of the gain adjustment signal at each temperature. More specifically, the setting value of the second gain variable circuit 60 is calculated such that the error between the gain adjustment signal output from the gain adjustment signal generation unit 80 and the compensation value of the gain adjustment signal is minimized. Here, the setting value of the second gain variable circuit 60 indicates a coefficient in each order of the function generated by the second gain variable circuit 60.

  In the gain temperature characteristic adjustment sequence of this example, the case where it is executed after the temperature sweep of the temperature compensation adjustment sequence is completed has been described. However, the temperature characteristic adjustment sequence may execute the temperature compensation adjustment sequence and the gain temperature characteristic adjustment sequence at each temperature set in step S102 even if the temperature sweep of the temperature compensation adjustment sequence is not completed. That is, since the temperature sweep of the temperature compensation adjustment sequence and the temperature sweep of the gain temperature characteristic adjustment sequence can be made common, the measurement time can be shortened. In this example, although the oscillator 200 has been described as an example, the gain temperature characteristic adjustment sequence can be similarly executed using the oscillator 300 or the oscillator 400. In this case, the gain adjustment signal generation unit 80 may be replaced with the gain adjustment signal generation unit 120 as appropriate.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It is apparent to those skilled in the art that various changes or modifications can be added to the above embodiment. It is also apparent from the scope of the claims that the embodiments added with such alterations or improvements can be included in the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 10 oscillation part, 11 1st control element, 12 2nd control element, 13 1st control terminal, 14 2nd control terminal, 20 approximate n order function generation circuit, 30 1st gain variable circuit, 31 operational amplifier, 32 resistance, 33 Variable feedback resistor, 34 resistance, 40 temperature compensation signal generator, 41 function generator, 42 voltage adder, 50 first temperature detection circuit, 60 second gain variable circuit

Claims (7)

In the oscillator
A quartz crystal,
A first control terminal and a second control terminal connected to the crystal unit;
A first temperature detection circuit that detects a temperature of a predetermined portion of the oscillator and generates a first temperature signal;
A temperature compensation signal generation unit that generates a first control signal that is input to the first control terminal and controls the oscillation frequency of the crystal unit based on the first temperature signal;
A variable gain amplifier that is input to the second control terminal based on a frequency control signal that controls the oscillation frequency of the crystal unit, and generates a second control signal that controls the oscillation frequency of the crystal unit;
A second temperature detection circuit that detects a temperature of a predetermined portion of the oscillator and generates a second temperature signal;
A gain adjustment signal generation unit configured to generate a gain adjustment signal for controlling the gain of the variable gain amplifier based on the second temperature signal.   The oscillator according to claim 1, wherein the second temperature detection circuit detects the second temperature signal independently of the first temperature signal. The oscillator according to claim 1, further comprising a storage unit that stores an adjustment value for adjusting the gain of the variable gain amplifier. The gain adjustment signal generation unit includes a determination circuit that determines a relationship between a value of the frequency control signal or the second control signal and a predetermined reference value.
The oscillator according to claim 3, wherein the storage unit stores a plurality of adjustment values corresponding to the determination result of the determination circuit. The method of adjusting an oscillator according to any one of claims 1 to 4,
A first step of inputting a predetermined constant value as the frequency control signal to the variable gain amplifier;
A second step of setting the temperature of the oscillator to an arbitrary temperature;
A third step of measuring a first external control signal input from outside the oscillator to the first control terminal;
A fourth step of monitoring a relationship between the first control signal output from the temperature compensation signal generation unit and a set value of the temperature compensation signal generation unit;
A fifth step of determining whether or not the first temperature sweep has ended, and returning to the second step if the first temperature sweep has not ended;
The temperature compensation signal generation such that an error between the first external control signal and the first control signal at each temperature set in the second step is minimized when the first temperature sweep is completed. And a sixth step of calculating the set value of the unit. A seventh step of setting the oscillator to a predetermined temperature;
An eighth step of measuring a gain characteristic of an oscillation frequency with respect to an input of the variable gain amplifier;
A ninth step of setting the temperature of the oscillator to an arbitrary temperature;
A tenth step of measuring a voltage input from outside the oscillator to the variable gain amplifier;
An eleventh step of measuring a gain adjustment signal output from the gain adjustment signal generation unit;
A twelfth step of determining whether or not a second temperature sweep has ended, and returning to the eighth step if the second temperature sweep has not ended;
The setting value of the variable gain amplifier is set such that the error between the gain adjustment signal output from the gain adjustment signal generation unit and the compensation value of the gain adjustment signal is minimized when the second temperature sweep is completed. The method of adjusting an oscillator according to claim 5, further comprising: calculating a thirteenth step.   7. The method of adjusting an oscillator according to claim 5, wherein the predetermined constant value is zero.

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