JP2009124401A - Oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oscillator which performs a highly precise temperature compensation on the basis of the respective temperature characteristics of an oscillation circuit and a crystal resonator. <P>SOLUTION: The oscillator includes: an oscillation part having a varactor which oscillates the crystal resonator; a temperature compensation part which compensates fluctuation of an oscillation frequency of the oscillation part by each temperature characteristic of the crystal resonator and the varactor; and a control part which controls the temperature compensation part. The temperature compensation part has: a first control signal output part which outputs three control signals with different voltage levels; a second control signal output part which outputs a reference signal at a voltage level having a primary temperature characteristic; a first comparison part which compares a first control signal with the reference signal to output a first signal in a low temperature region; a second comparison part which compares a second control signal with the reference signal to output a second signal in a high temperature region; a third comparison part which compares a third control signal with the reference signal to output a third signal in a normal temperature region; a first current control part which controls a current value of the first signal; a second current control part which controls a current value of the second signal; and a signal synthesis part which synthesizes the first to third signals. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a temperature compensation type oscillation device using a crystal resonator.

  In recent portable electronic devices, a small and highly accurate crystal oscillation device for generating a reference clock signal is essential. However, the oscillation frequency of the crystal resonator used in the crystal oscillation device has a temperature characteristic having an n-order component (n is a real number of 3 or more). That is, as shown in FIG. 9A in which the horizontal axis is the ambient temperature Ta and the vertical axis is the oscillation frequency f, the oscillation frequency f of the crystal oscillation device without temperature compensation is the difference between the maximum value and the minimum value. Becomes an n-order curve 101A of about 10 ppm to 30 ppm. The ambient temperature Ta is assumed to be about −30 ° C. to + 80 ° C. Therefore, an ideal control voltage curve 102A shown in FIG. 9B in which the horizontal axis is the ambient temperature Ta and the vertical axis is the control voltage Vc is generated, and the control voltage Vc indicated by the curve 102A is generated as a crystal oscillation device. 9 (c), df / dTa = 0 and the oscillation frequency f is substantially independent of temperature.

  As described above, in the temperature compensation method in the crystal oscillation device, for example, a variable capacitance diode that is a frequency adjusting element is connected to the crystal oscillation device, and the approximate n for compensating the temperature characteristics of the crystal resonator to the variable capacitance diode. There is a method of stabilizing the temperature characteristic of the oscillation frequency by applying a control voltage having the following temperature characteristic. However, in practice, since it is technically difficult to generate the ideal control voltage Vc shown in FIG. 9B, in general, a control voltage having a pseudo third-order temperature characteristic is obtained by various methods. Generated and temperature compensation of the oscillation frequency is performed.

  FIG. 10 is a block diagram showing a crystal oscillation device with a temperature compensation function disclosed in Patent Document 1. In FIG. 10 includes a constant voltage circuit 12 as a first analog signal generation circuit that generates and outputs a predetermined voltage value independent of the ambient temperature, and a voltage value proportional to the ambient temperature. The temperature sensor circuit 13 as a second analog signal generation circuit for generating and outputting the voltage, the constant voltage output from the constant voltage circuit 12 and the voltage output proportional to the temperature from the temperature sensor circuit 13 are received, A control circuit 14 that generates a control voltage Vc that performs a polygonal line approximation using a straight line that is a negative cubic curve for compensating the temperature characteristics of the crystal resonator over the temperature region, and a control voltage Vc from the control circuit 14 The voltage control crystal oscillation circuit (hereinafter referred to as “VCXO”) 15 whose oscillation frequency is controlled to a predetermined value by the control voltage Vc, and the control voltage Vc output from the control circuit 14. Against it, and a ROM / RAM circuit 16 for storing temperature compensating coefficient for compensating the temperature characteristic of the control voltage Vc for optimizing the oscillation frequency VCXO15 outputs. Here, the ambient temperature may be the temperature of the VCXO 15 or the temperature of the crystal oscillation device 10.

  In the crystal oscillating device 10, the possible range of the ambient temperature is the first temperature region, the second temperature region, the third temperature region, the fourth temperature region, and the fifth temperature region that are continuous from the low temperature side to the high temperature side. Control signals y 1, y 2, y 3, y 4, and y 5 corresponding to each of the five temperature regions are sequentially generated by the constant voltage circuit 12 and the temperature sensor circuit 13. The control signals y1, y2, y3, y4, and y5 are input to the MAX circuit 14a and the MIN circuit 14b included in the control circuit 14, thereby generating a control signal y7 that approximates a cubic function depending on the ambient temperature. The

  In the crystal oscillation device 10 shown in FIG. 10, control signals y1, y2, y3, y4, and y5 adjusted by the ROM / RAM circuit 16 that stores the temperature compensation coefficient are input to the MAX circuit 14a and the MIN circuit 14b. Since the signal y7 is output, the temperature compensation coefficient is accurately set in the output of the temperature compensation circuit depending on the proportionality coefficient in the temperature characteristics of the control signals y1, y2, y3, y4, and y5 from the characteristics of the MAX circuit 14a and the MIN circuit 14b. There is a problem that it may not be reflected well.

  FIG. 11 is a block diagram illustrating a temperature compensation circuit included in the crystal oscillation device disclosed in Patent Document 1. In FIG. The function generation circuit included in the temperature compensation circuit illustrated in FIG. 11 has substantially the same configuration as the control circuit 14 illustrated in FIG. That is, the function generation circuit generates a tertiary control voltage αVc corresponding to the third-order temperature characteristic coefficient α within a predetermined temperature range in accordance with output signals of the constant voltage circuit 12 and the temperature sensor circuit 13. 14A, a primary characteristic circuit 17 that generates a primary control voltage βVc corresponding to a primary temperature characteristic coefficient β within a predetermined temperature range, and a zero-order temperature characteristic coefficient γ within a predetermined temperature range, that is, A zero-order characteristic circuit 18 that generates a zero-order control voltage γVc that does not depend on temperature within a predetermined temperature range, and the value of the inflection point temperature Ti is adjusted according to the output signal of the temperature sensor circuit 13, and MAX / MIN. A Ti adjusting circuit 19 for outputting a signal to the circuit 14A and the primary characteristic circuit 17;

  The function generation circuit shown in FIG. 11 is configured to improve the problem of the crystal oscillation device 10 shown in FIG. That is, when the function generation circuit shown in FIG. 11 is applied to the crystal oscillation device 10, the third-order temperature characteristic coefficient adjustment and inflection are performed by the MAX circuit / MIN circuit 14A with respect to the control signals y1, y2, y3, y4, and y5. A tertiary control voltage αVc subjected to point coefficient adjustment is generated.

  Further, the primary control voltage βVc subjected to the first-order temperature characteristic coefficient adjustment in the primary characteristic circuit 17 is output, and the zero-order control voltage γVc subjected to the zero-order temperature characteristic coefficient adjustment in the zero-order characteristic circuit 18. Is output. By adding these control voltages αVc, βVc, and γVc, a control signal Vc that accurately reflects the temperature compensation coefficient can be output.

  However, even if the control signal Vc that accurately reflects the temperature compensation coefficient is used, the temperature characteristics of the voltage controlled crystal oscillation circuit (VCXO) 15 shown in FIG. Since the temperature characteristic coefficient is higher than the next, high accuracy of within ± 0.5 ppm of fundamental frequency fluctuation error cannot be satisfied.

FIG. 12 is a diagram illustrating a characteristic change of the control voltage Vc with respect to a temperature compensation coefficient change in the crystal oscillation device disclosed in Patent Document 1. In FIG. The control voltage Vc has a temperature characteristic approximated to a cubic function represented by the following formula (1).
Vc = αc (T−Tc) ³ + βc (T−Tc) + γc (1)
(Where T is the ambient temperature, αc is the third-order coefficient, βc is the first-order coefficient, γc is the zero-order coefficient, and Tc is the inflection point of the function indicating the control voltage Vc.)

  FIG. 12A is a diagram showing a change in the characteristic of the control voltage Vc due to a change in the third-order temperature compensation coefficient αc in the equation (1). FIG. 12B is a diagram showing a change in the characteristic of the control voltage Vc due to a change in the primary temperature compensation coefficient βc in the equation (1). FIG. 12C is a diagram showing a change in the characteristic of the control voltage Vc due to a change in the zeroth-order temperature compensation coefficient γc in the equation (1). FIG. 12D is a diagram showing a change in the characteristic of the control voltage Vc due to a change in the temperature compensation coefficient Tc at the inflection point in the equation (1).

  FIG. 13A is a diagram illustrating the characteristics of the control voltage Vc generated by the function generation circuit illustrated in FIG. FIG. 13B is a diagram showing the difference between the control voltage Vc shown in FIG. 13A and the ideal control voltage. FIG. 13C is a diagram showing a fundamental frequency fluctuation error Δf that is an error from f0 of the output frequency after temperature compensation.

  The control voltage Vc shown in FIG. 13A is an output signal of a function generation circuit for generating an approximate cubic function, but has some errors compared to an ideal cubic curve. The cause may be a diffusion variation in a semiconductor IC manufacturing process, an error due to a layout in the IC chip, or the like. Due to the error ΔVc of the control signal Vc, the error from the ideal first-order approximation in the voltage-controlled crystal oscillation circuit 15, and the error from the ideal third-order approximation in the crystal resonator, the basic frequency fluctuation error Δf is about ± 1 ppm.

Japanese Patent No. 3160299 Japanese Patent Laid-Open No. 8-288741

  A crystal oscillation device included in an electronic device equipped with a GPS function is required to have an accuracy that the fundamental frequency fluctuation error Δf is within ± 0.5 ppm. However, when the temperature characteristics of the crystal resonator are approximated using a third-order function generation circuit, as in the above-described crystal oscillation device with a temperature compensation function, the accuracy of the fundamental frequency fluctuation error Δf is within ± 0.5 ppm. I'm not satisfied. In addition, the influence of the temperature characteristics of the voltage controlled crystal oscillation circuit cannot be ignored.

  In addition, since the crystal oscillation device described above uses A / D conversion for polygonal line approximation for generating a control voltage for temperature compensation, quantization noise is generated and it is inevitable in principle from frequency jump. . Further, since a clock signal generation circuit is necessary, clock noise is mixed. Since crystal oscillators used in electronic devices are used in combination with various devices in electronic devices, noise generated from crystal oscillators affects other devices, causing deterioration of electronic device characteristics and malfunctions. Cause. Therefore, a low-noise crystal oscillation device is desirable.

  As described above, the temperature characteristics of the crystal resonator are generally approximated by a cubic function. However, in order to approximate the function with higher accuracy, it is necessary to approximate the temperature characteristic in consideration of a larger order. Further, the temperature characteristics of the voltage controlled crystal oscillation circuit provided with the variable capacitance element are also approximated by a linear function. However, since the error from the linear function cannot be ignored, it is necessary to approximate the function with higher accuracy as well. is there. That is, it is necessary to realize temperature compensation based on the temperature characteristics of the voltage controlled crystal oscillation circuit and the crystal resonator. Therefore, the function generation circuit used in the crystal oscillation device does not generate a control voltage approximated to a function of the third order or lower, but generates a control voltage approximated to a function of the fourth order or higher. It is necessary to realize without deteriorating other various characteristics.

  An object of the present invention is to provide an oscillation device that can perform highly accurate temperature compensation based on each temperature characteristic of an oscillation circuit and a crystal resonator with low noise.

  The present invention includes an oscillation unit including a variable capacitance element that oscillates a crystal resonator, and a temperature compensation unit that compensates for fluctuations in the oscillation frequency of the oscillation unit due to the temperature characteristics of the crystal resonator and the variable capacitance element. A control unit that controls the temperature compensation unit, wherein the temperature compensation unit is independent of the ambient temperature and outputs three control signals having different voltage levels. An output unit, a second control signal output unit that outputs a reference control signal of a voltage level having a temperature characteristic approximated to a linear function that depends on the ambient temperature, and an output from the first control signal output unit The first control signal is compared with the reference control signal output from the second control signal output unit, and the first signal depending on the ambient temperature in the low temperature region is output. Comparison unit and the first control The second control signal output from the signal output unit and the reference control signal output from the second control signal output unit are compared, and a second signal depending on the ambient temperature in the high temperature region is obtained. The second comparison unit to output, the third control signal output from the first control signal output unit and the reference control signal output from the second control signal output unit are compared, and the normal temperature A third comparator that outputs a third signal that depends on the ambient temperature in the region, and a first current controller that controls the current value of the first signal output from the first comparator A second current control unit that controls a current value of the second signal output from the second comparison unit, and a current output from the first comparison unit that is output from the first comparison unit. The first signal whose value is controlled is output from the second comparison unit, and the second signal A signal synthesis unit that synthesizes the second signal, the current value of which is controlled by the current control unit, and the third signal output from the third comparison unit, and the control unit includes: The first control signal output unit is controlled to adjust the voltage levels of the first control signal and the second control signal, and the first current control unit and the second current control unit are controlled. And an oscillation device that adjusts each current value of the first signal and the second signal.

  In the oscillation device, the signal synthesized by the signal synthesis unit of the temperature compensation unit is applied to the variable capacitance element of the oscillation unit.

  In the oscillation device, the second control signal output unit includes a diode, and the voltage level of the reference control signal is a forward voltage of the diode.

  In the oscillation device, the first signal output from the first comparison unit and the second signal output from the second comparison unit have the same polarity.

  In the oscillation device, the control unit adjusts the voltage level of the first control signal, adjusts the voltage level of the second control signal, adjusts the current value of the first signal, and the second signal. The current value of each is adjusted independently.

  In the oscillation device, the control unit performs adjustment of the first control signal voltage level and adjustment of the voltage level of the second control signal in conjunction with each other.

  In the oscillation device, the control unit adjusts the current value of the first signal and the current value of the second signal in conjunction with each other.

  In the oscillation device, the first control signal output unit has a plurality of resistors connected in series, and each voltage level of the first control signal and the second control signal is selectable. The voltage level is based on the voltage division ratio selected by the control unit from among the voltage division ratios.

In the oscillation device, the first current control unit and the second current control unit are configured by a current mirror circuit capable of changing a mirror ratio,
Each current value of the first signal and the second signal is a current value based on a mirror ratio selected by the control unit from a plurality of selectable mirror ratios.

  In the oscillation device, the low temperature region is a temperature range from a midpoint of a temperature of an intersection of the first control signal and the reference control signal and a temperature of an intersection of the third control signal and the reference control signal. The high temperature region is set to a high temperature region from the midpoint of the temperature of the intersection of the second control signal and the reference control signal and the temperature of the intersection of the third control signal and the reference control signal. The normal temperature region is set to a region between the low temperature region and the high temperature region.

  The present invention provides an oscillator including a crystal resonator and the oscillation device that oscillates the crystal resonator.

  According to the oscillation device of the present invention, the first-order control signal output by the control unit is used to output a higher-order component included in the control signal of the approximate n-order function (n is an integer of 3 or more) output from the temperature compensation unit. Can be adjusted by control of the first current control unit and the second current control unit, so that variations in the oscillation frequency due to the temperature characteristics of the oscillation circuit and the crystal resonator can be accurately performed in a wide temperature range. Can be compensated. Further, the adjustment of the higher-order component included in the control signal is performed by the extreme value of the approximate n-order function by the control of the first control signal output unit, and the approximation by the control of the first current control unit and the second current control unit. Since this is performed by changing the differential coefficient of the n-order function, each order noise is not synthesized. Therefore, temperature compensation can be performed with low noise.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a block diagram illustrating a temperature-compensated crystal oscillation device according to an embodiment. As shown in FIG. 1, the temperature-compensated crystal oscillation device (hereinafter referred to as “TCXO”) includes a regulator circuit 21, a temperature compensation circuit 58, a control unit 510, and a voltage-controlled oscillation circuit (hereinafter referred to as “VCO”). 59). The temperature compensation circuit 58 includes a constant voltage circuit 51, a temperature sensor circuit 52, an approximate n-order function generation circuit 53, a linear function generation circuit 54, a zero-order function generation circuit 55, and an inflection point adjustment circuit 56. And an adder 61. The VCO 59 includes an amplifier 63 and a variable capacitor 64.

  The regulator circuit 21 generates a stabilized constant voltage from the power supply voltage Vcc and supplies it to the constant voltage circuit 51 of the temperature compensation circuit 58 and the amplifier 63 of the VCO 59. The temperature compensation circuit 58 generates a control signal Vc for performing temperature compensation of the oscillation frequency according to the ambient temperature. Control unit 510 stores a temperature compensation coefficient for adjusting the temperature characteristic of control signal Vc, and controls temperature compensation circuit 58. The control signal Vc generated by the temperature compensation circuit 58 is input to the VCO 59. The VCO 59 oscillates the connected crystal resonator 57 and outputs an oscillation signal from the terminal Fout. The control signal Vc is applied to the variable capacitance element 64 of the VCO 59, and the variable capacitance element 64 becomes a load capacitance of the amplifier 63 corresponding to the control signal Vc.

  The approximate n-order function generation circuit 53 included in the temperature compensation circuit 58 generates an approximate n-order function control signal Vn corresponding to the n-th order temperature characteristic coefficient in accordance with the output signals from the constant voltage circuit 51 and the temperature sensor circuit 52. Generate. The linear function generation circuit 54 generates a linear function control signal V1 that depends on the ambient temperature in accordance with the output signals from the constant voltage circuit 51 and the temperature sensor circuit 52. In addition, the zero-order function generation circuit 55 generates a zero-order function control signal V 0 that does not depend on the ambient temperature, in accordance with the output signal from the constant voltage circuit 51.

  The inflection point adjustment circuit 56 adjusts the value of the inflection point temperature Ti of the approximate n-order function control signal Vn generated by the approximate n-order function generation circuit 53. The adder 61 adds the control signal Vn generated by the approximate n-order function generation circuit 53, the control signal V1 generated by the first-order function generation circuit 54, and the control signal V0 generated by the zero-order function generation circuit 55, A control signal Vc is output. The control signal Vc output from the temperature compensation circuit 58 is input to the VCO 59.

  FIG. 2 is a block diagram showing an internal configuration of the approximate n-order function generation circuit 53 included in the temperature compensation circuit 58 provided in the temperature compensation type crystal oscillation device shown in FIG. 2 includes a low temperature region comparator 111, a high temperature region comparator 112, a normal temperature region comparator 113, a low temperature differential coefficient variable circuit 114, a high temperature differential coefficient variable circuit 115, And a signal synthesis circuit 116.

  The low temperature region comparator 111 compares the control signal VL output from the constant voltage circuit 51 with the control signal Vs output from the temperature sensor circuit 52, and outputs a control signal IL corresponding to the magnitude relationship. The high temperature region comparator 112 compares the control signal VH output from the constant voltage circuit 51 with the control signal Vs output from the temperature sensor circuit 52, and outputs a control signal IH corresponding to the magnitude relationship. The normal temperature region comparator 113 compares the control signal Vc output from the constant voltage circuit 51 and the control signal Vs output from the temperature sensor circuit 52, and outputs a control signal Ic corresponding to the magnitude relationship.

  The voltage levels of the control signals VL, VH, Vc output from the constant voltage circuit 51 are different. FIG. 3 is a circuit diagram (a) showing the constant voltage circuit 51 and a diagram (b) showing temperature characteristics of the output voltages VL, VH and Vc. As shown in FIG. 3A, the constant voltage circuit 51 has a plurality of resistors connected in series, and the voltages of the control signals VL, VH, and Vc are determined by the voltage dividing ratio. The constant voltage circuit 51 includes two switch units that select one voltage dividing ratio from three different voltage dividing ratios. One of the two switch sections is provided for selecting the voltage level of the control signal VL, and the other is provided for selecting the voltage level of the control signal VH. The two switch units are controlled by signals (VL control signal, VH control signal) from the control unit 510.

  The voltage level of the control signal Vs output from the temperature sensor circuit 52 varies depending on the ambient temperature. FIG. 4A is a circuit diagram showing the temperature sensor circuit 52, and FIG. 4B is a diagram showing temperature characteristics of the output voltage Vs. As shown in FIG. 4A, the temperature sensor circuit 52 includes a diode 22 having a primary temperature characteristic of about −4 mV / ° C. The temperature sensor circuit 52 may be a sensor using a current proportional to Vt of the bandgap reference or a sensor using a temperature characteristic of resistance. In the present embodiment, as shown in FIG. 4B, the temperature characteristic of the voltage level of the control signal Vs output from the temperature sensor circuit 52 is represented by a negative linear function. Depending on the number of diodes, the output bias of the temperature sensor circuit 52 and the slope of the primary temperature characteristic change.

  The low temperature differential coefficient variable circuit 114 adjusts the current value of the control signal IL output from the low temperature region comparator 111 according to the low temperature control signal output from the control unit 510 and outputs the control signal IL ′. Further, the high temperature differential coefficient variable circuit 115 adjusts the current value of the control signal IH output from the high temperature region comparator 112 according to the high temperature control signal output from the control unit 510 and outputs the control signal IH ′. To do.

The signal synthesis circuit 116 synthesizes the control signal I _L ′ output from the low temperature differential coefficient variable circuit 114, the control signal Ic output from the normal temperature region comparator 113, and I _H ′ output from the high temperature differential coefficient variable circuit 115. Then, the approximate n-order function control signal Vn is output. FIG. 5 is a circuit diagram showing the signal synthesis circuit 116 included in the approximate n-order function generation circuit 53. The signal synthesis circuit 116 selects the maximum voltage from the input voltages Vnl and Vnc that are input, and outputs Vn1. Thereafter, the minimum voltage is selected from the voltage outputs Vn1 and Vnh, and the voltage output Vn is output.

  FIG. 6 is a diagram for explaining the principle of the control signal Vn generated by the approximate n-order function generation circuit 53 included in the temperature compensation circuit 58 and each temperature region. As shown in FIG. 6A, the output voltages VL, VH, and Vc of the constant voltage circuit 51 shown in FIG. 3B are compared with the output voltage Vs of the temperature sensor circuit 52 shown in FIG. To obtain the intersection of these voltages. Next, as shown in FIG. 6C, the temperature TPL at the intersection PL between the output voltage VL and the output voltage Vs, the temperature TPc at the intersection Pc between the output voltage Vc and the output voltage Vs, and the output voltage VH and the output voltage. The temperature TPH of the intersection PH with Vs is obtained. Next, the low temperature region from the middle point of the temperature TPL and the temperature TPc is set as the low temperature region in the present embodiment, and the middle point of the temperature TPL and the temperature TPc to the middle point of the temperature TPc and the temperature TPH in the present embodiment. The temperature region is set, and the high temperature region is set to the high temperature region in the present embodiment from the midpoint of the temperatures TPc and TPH. Each temperature region set in this way becomes the operating temperature range of each comparator included in the approximate n-order function generation circuit 53.

  Next, as shown in FIG. 6B, the difference between the output voltage Vs of the temperature sensor circuit 52 and the output voltage of the constant voltage circuit 51 in each temperature region is output for each temperature region. That is, the low temperature region comparator 111 included in the approximate n-order function generation circuit 53 outputs the difference between the output voltage Vs and the output voltage VL in the low temperature region, and the normal temperature region comparator 113 outputs the difference between the output voltage Vs in the normal temperature region. The difference between the output voltages Vc is output, and the high temperature region comparator 112 outputs the difference between the output voltage Vs and the output voltage VH in the high temperature region.

  As described above, the output of the low temperature region comparator 111 is input to the signal synthesis circuit 116 via the low temperature differential coefficient variable circuit 114, and the output of the high temperature region comparator 112 is input via the high temperature differential coefficient variable circuit 115. As shown in FIG. 2, the low temperature differential coefficient variable circuit 114 and the high temperature differential coefficient variable circuit 115 are configured by a current mirror circuit, and the output of the current mirror circuit is obtained by reversing the polarity. Therefore, the output of the low temperature region comparator 111 via the low temperature differential coefficient variable circuit 114 and the output of the high temperature region comparator 112 via the high temperature differential coefficient variable circuit 115 are respectively inverted and input to the signal synthesis circuit 116. The signal synthesis circuit 116 can generate the control signal Vn of the approximate cubic curve shown in FIG. 6B from the output in each temperature region.

The crystal unit 57 has a temperature characteristic approximated to an n-order function represented by the following formula (2).
Fc = a _n (T−Tx) ⁿ + a _n−1 (T−Tx) ⁿ⁻¹ +... + B (T−Tx) + c (2)
(However, Fc is the output frequency of the crystal oscillator 57, T is the ambient temperature, _{a n} is the n-th order coefficient, b is 1 order coefficient, c is 0 order coefficient, Tx a variation of a function showing the output frequency Fc It is a music point.)

The VCO 59 having the variable capacitance element 64 has a temperature characteristic approximated to an n-order function represented by the following formula (3).
^{_{Fd = d n (T-T1}} ) n + d n-1 (T-T1) n-1 + ··· + e (T-T1) + g ... (3)

(However, Fd is the output frequency of the VCO59, T is the ambient temperature, _{d n} is an n-th order coefficient, e is 1 order coefficient, g is 0 order coefficient, T1 is the inflection point of the function representing the output frequency Fd is there.)

From the above formulas (2) and (3), the temperature characteristics of the entire VCO 59 including the crystal unit 57 and the variable capacitance element 64 are approximated by an n-order function represented by the following formula (4).
F = α _n (T−T0) ⁿ + α _n−1 (T−T0) ⁿ⁻¹ +... + Β (T−T0) + γ (4)
(Where F is the output frequency of the VCO 59 oscillating the crystal unit, T is the ambient temperature, α _n is the nth order coefficient, β is the first order coefficient, γ is the 0th order coefficient, and T0 is the output frequency F. (This is the inflection point of the function shown.)

  In the TCXO (temperature compensated crystal oscillation device) of the present embodiment, the temperature compensation circuit 58 compensates the temperature characteristics of the entire circuit including the crystal resonator 57 and the variable capacitance element 64 having the temperature characteristics described above. A constant oscillation frequency is output regardless of the ambient temperature. As described above, the temperature compensation circuit 58 of the present embodiment includes the approximate n-order function generation circuit 53, the primary function generation circuit 54, and the zero-order function generation circuit 55, and the control signal generated by these circuits is received. By applying voltage to the variable capacitance element of the VCO 59, temperature compensation of the temperature characteristics of the crystal resonator 57 and the variable capacitance element 64 is performed. Note that n is an integer of 3 or more.

  FIG. 7 shows an output waveform of the approximate n-order function generation circuit 53 and a circuit diagram of the constant voltage circuit 51 included in the temperature compensation circuit 58 provided in the temperature compensation type crystal oscillation device. By controlling the input signal VL of the low temperature region comparator 111 and the input signal VH of the high temperature region comparator 112 included in the approximate n-order function generation circuit 53 by the VL control signal and the VH control signal output from the control unit 510, respectively. Then, the operating temperature range of each comparator is changed, the extreme value of the output signal of the approximate n-order function generation circuit 53 is changed, and the coefficient of third order or higher is changed. Note that the VL control signal and the VH control signal may be controlled independently by the control unit 510 or may be controlled in conjunction with each other.

  The example shown in FIG. 7B is a diagram showing a case where the output voltages VL and VH of the constant voltage circuit 51 are set to standard values. The example shown in FIG. 7A is a diagram illustrating a case where the output voltage VL of the constant voltage circuit 51 is set higher and the output voltage VH is set lower than the example shown in FIG. 7B. Further, the example shown in FIG. 7C is a diagram showing a case where the output voltage VL of the constant voltage circuit 51 is lowered and the output voltage VH is set higher than the example shown in FIG. 7B. is there.

  As shown in FIG. 7A, when the output voltage VL is set high, the intersection point PL between the output voltage VL and the output voltage Vs shown in FIG. 6 moves, and the temperature TPL at the intersection point PL becomes low. And the midpoint of the temperature TPc is also lowered. As a result, the low temperature region and the normal temperature region change, and the maximum value of the output signal of the approximate n-order function generation circuit 53 increases. Similarly, when the output voltage VH is set low, the intersection PH between the output voltage VH and the output voltage Vs shown in FIG. 6 moves and the temperature TPH at the intersection PH increases, so that the midpoint between the temperature TPH and the temperature TPc is also Get higher. As a result, the high temperature region and the normal temperature region change, and the minimum value of the output signal of the approximate n-order function generation circuit 53 decreases.

  In this way, by controlling the output voltages VL and VH of the constant voltage circuit 51, the operating temperature range of each comparator can be changed, and the extreme value of the output signal of the approximate nth-order function generation circuit 53 can be changed. The third-order or higher-order coefficient of the output signal of the approximate n-order function generation circuit 53 can be changed.

  FIG. 8 shows the output waveform of the approximate n-order function generation circuit 53 included in the temperature compensation circuit 58 provided in the temperature-compensated crystal oscillation device, the low-temperature differential coefficient variable circuit 114 and the high-temperature differential function included in the approximate n-order function generation circuit 53. Each circuit diagram of the coefficient variable circuit 115 is shown. By controlling the output signal IL of the low temperature region comparator 111 and the output signal IH of the high temperature region comparator 112 included in the approximate n-order function generation circuit 53 by the low temperature control signal and the high temperature control signal output from the control unit 510, respectively. Then, the low-temperature and high-temperature differential coefficients of the output signal of the approximate n-order function generation circuit 53 are changed to change the third-order or higher coefficients. The low temperature control signal and the high temperature control signal may be controlled independently by the control unit 510 or may be controlled in conjunction with each other.

  The example shown in FIG. 8B is a diagram showing a case where the setting of the low temperature differential coefficient variable circuit 114 and the high temperature differential coefficient variable circuit 115 is standard. 8A is compared with the example shown in FIG. 8B, the current value of the control signal IL ′ output from the low temperature differential coefficient variable circuit 114 and the high temperature differential coefficient variable circuit 115. It is a figure which shows the case where the electric current value of the control signal IH 'performed is made low. 8C is different from the example shown in FIG. 8B in that the current value of the control signal IL ′ output from the low-temperature differential coefficient variable circuit 114 and the high-temperature differential coefficient variable circuit 115. It is a figure which shows the case where the electric current value of control signal IH 'output from is made high.

  As shown in FIG. 8A, if the mirror ratio of the current mirror circuit in the low temperature differential coefficient variable circuit 114 and the high temperature differential coefficient variable circuit 115 is reduced, the current of the control signal IL ′ output from the low temperature differential coefficient variable circuit 114 Since the current value of the control signal IH ′ output from the value and high temperature differential coefficient variable circuit 115 is small, the slope of the straight line indicating the control signal Vn in the low temperature region and the high temperature region is small. On the other hand, as shown in FIG. 8C, when the mirror ratio of the current mirror circuit in the low temperature differential coefficient variable circuit 114 and the high temperature differential coefficient variable circuit 115 is increased, the control signal IL ′ output from the low temperature differential coefficient variable circuit 114. Current value and the current value of the control signal IH ′ output from the high temperature differential coefficient variable circuit 115 become large, and the slope of the straight line indicating the control signal Vn in the low temperature region and the high temperature region becomes large. The change in the slope of the straight line indicating the control signal Vn in the low temperature region and the high temperature region means a change in the fourth or higher order component of the control signal Vn.

  In this way, by controlling the mirror ratio of the current mirror circuit in the low-temperature differential coefficient variable circuit 114 and the high-temperature differential coefficient variable circuit 115, the low-temperature and high-temperature differential coefficients of the output signal of the approximate n-order function generation circuit 53 are changed. Therefore, the third or higher order coefficient of the output signal of the approximate nth order function generation circuit 53 can be changed.

  By using the extreme value control shown in FIG. 7 and the differential coefficient control shown in FIG. 8 in combination, the control signal having the n-th order coefficient output from the approximate n-order function generation circuit 53 is more than the third order. Each coefficient can be changed in a complex manner. Therefore, the temperature characteristic data of the frequency of the signal output from the TCXO including the crystal resonator 57 and the variable capacitance element 64 is acquired in advance, and is output from the control unit 510 for extreme value control based on the data. If the optimum values of the VL control signal and the VH control signal and the optimum values of the low temperature control signal and the high temperature control signal output from the control unit 510 for the differential coefficient control are obtained, the optimum values according to the ambient temperature are obtained. Optimal temperature compensation can be performed.

  On the other hand, regarding the noise generated in the temperature compensation circuit 58, the effect of the approximate n-order function generation circuit 53 of this embodiment will be described. The approximate quintic function generator shown in FIG. 2 of the international publication No. WO 2004/025824 has the output signals of the quintic component generator, the quaternary component generator, the tertiary component generator and the primary component generator. Synthesize. In this case, noise included in the output signal of each component generation unit is also synthesized, so that low-temperature and high-temperature noise deteriorates. However, the approximate n-order function generation circuit of the present embodiment changes the extreme value of the output signal approximated by the n-order function by extreme value control and changes the low-temperature and high-temperature differential coefficients by differential coefficient control. There is no such noise synthesis. Therefore, according to the present embodiment, temperature compensation can be performed with low noise.

  As described above, according to the TCXO of the present embodiment, the control signal Vn of the approximate n-order function is controlled while the noise near normal temperature is not deteriorated and the deterioration of noise near low temperature and high temperature is suppressed. High-precision temperature compensation can be performed.

  The oscillation device according to the present invention is useful as a temperature compensated oscillation device using a crystal resonator.

1 is a block diagram illustrating a temperature-compensated crystal oscillation device according to an embodiment. The block diagram which shows the internal structure of the approximate n-order function generation circuit 53 which the temperature compensation circuit 58 provided in the temperature compensation type crystal oscillation apparatus shown in FIG. A circuit diagram showing the constant voltage circuit 51 (a) and a diagram showing temperature characteristics of the output voltages VL, VH, Vc (b) The circuit diagram (a) which shows the temperature sensor circuit 52, and the figure which shows the temperature characteristic of output voltage Vs (b) Circuit diagram showing the signal synthesis circuit 116 included in the approximate n-order function generation circuit 53 The figure explaining the principle of the control signal Vn produced | generated by the approximate n-order function production | generation circuit 53 which the temperature compensation circuit 58 has, and each temperature area | region The output waveform of the approximate n-order function generation circuit 53 included in the temperature compensation circuit 58 provided in the temperature compensation type crystal oscillation device and the circuit diagram of the constant voltage circuit 51 The output waveform of the approximate n-order function generation circuit 53 included in the temperature compensation circuit 58 provided in the temperature-compensated crystal oscillation device, the low-temperature differential coefficient variable circuit 114 and the high-temperature differential coefficient variable circuit 115 included in the approximate n-order function generation circuit 53. Each circuit diagram Temperature characteristics of oscillation frequency of crystal oscillator Block diagram showing a crystal oscillation device with a temperature compensation function disclosed in Patent Document 1 FIG. 2 is a block diagram showing a temperature compensation circuit included in a crystal oscillation device disclosed in Patent Document 1 The figure which shows the characteristic change of the control voltage Vc with respect to the coefficient change for temperature compensation in the crystal oscillation apparatus disclosed by patent document 1 FIG. 11A shows characteristics of the control voltage Vc generated by the function generation circuit shown in FIG. 11, FIG. 13B shows the difference between the control voltage Vc shown in FIG. 13A and the ideal control voltage, and after temperature compensation. (C) which shows fundamental frequency fluctuation error (DELTA) f which is an error with f0 of output frequency of

Explanation of symbols

21 Regulator circuit 51 Constant voltage circuit 52 Temperature sensor circuit 53 Approximate nth order function generation circuit 54 Primary function generation circuit 55 0th order function generation circuit 56 Inflection point adjustment circuit 57 Crystal oscillator 58 Temperature compensation circuit 59 Voltage control oscillation circuit ( VCO)
63 Amplifier 64 Variable capacitance element 510 Control unit 111 Low temperature region comparator 112 High temperature region comparator 113 Normal temperature region comparator 114 Low temperature differential coefficient variable circuit 115 High temperature differential coefficient variable circuit 116 Signal synthesis circuit

Claims (11)

An oscillation unit including a variable capacitance element that oscillates a crystal unit;
A temperature compensation unit that compensates for fluctuations in the oscillation frequency of the oscillation unit due to the temperature characteristics of the crystal resonator and the variable capacitance element;
A control unit for controlling the temperature compensation unit,
The temperature compensation unit is
A first control signal output unit that outputs three control signals having different voltage levels, independent of the ambient temperature;
A second control signal output unit that outputs a reference control signal of a voltage level having a temperature characteristic approximate to a linear function depending on the ambient temperature;
The first control signal output from the first control signal output unit is compared with the reference control signal output from the second control signal output unit, and depends on the ambient temperature in a low temperature region A first comparator that outputs a first signal;
The second control signal output from the first control signal output unit is compared with the reference control signal output from the second control signal output unit, and depends on the ambient temperature in the high temperature region A second comparison unit that outputs a second signal;
The third control signal output from the first control signal output unit is compared with the reference control signal output from the second control signal output unit, and depends on the ambient temperature in the normal temperature region A third comparison unit for outputting a third signal;
A first current control unit that controls a current value of the first signal output from the first comparison unit;
A second current control unit that controls a current value of the second signal output from the second comparison unit;
The first signal output from the first comparison unit, the current value of which is controlled by the first current control unit, and the current value output from the second comparison unit and output from the second current control unit. And a second signal synthesizer that synthesizes the third signal output from the third comparison unit.
The control unit controls the first control signal output unit to adjust voltage levels of the first control signal and the second control signal, and controls the first current control unit and the second control signal. An oscillation device, wherein a current control unit is controlled to adjust each current value of the first signal and the second signal. The oscillation device according to claim 1,
An oscillation device, wherein a signal synthesized by the signal synthesis unit of the temperature compensation unit is applied to the variable capacitance element of the oscillation unit. The oscillation device according to claim 1,
The second control signal output unit includes a diode;
The voltage level of the reference control signal is a forward voltage of the diode. The oscillation device according to claim 1,
The oscillation device, wherein the first signal output from the first comparison unit and the second signal output from the second comparison unit have the same polarity. The oscillation device according to claim 1,
The control unit adjusts the voltage level of the first control signal, adjusts the voltage level of the second control signal, adjusts the current value of the first signal, and adjusts the current value of the second signal. An oscillation device characterized by performing each independently. The oscillation device according to claim 1,
The oscillating device according to claim 1, wherein the control unit adjusts the voltage level of the first control signal and the voltage level of the second control signal in conjunction with each other. The oscillation device according to claim 1,
The control device performs adjustment of the current value of the first signal and the adjustment of the current value of the second signal in conjunction with each other. The oscillation device according to claim 1,
The first control signal output unit has a plurality of resistors connected in series,
The voltage level of each of the first control signal and the second control signal is a voltage level based on a voltage division ratio selected by the control unit from a plurality of selectable voltage division ratios. apparatus. The oscillation device according to claim 1,
The first current control unit and the second current control unit are configured by a current mirror circuit capable of changing a mirror ratio,
Each of the current values of the first signal and the second signal is a current value based on a mirror ratio selected by the control unit from a plurality of selectable mirror ratios. The oscillation device according to claim 1,
The low temperature region is set to a low temperature region from the midpoint temperature of the intersection of the first control signal and the reference control signal, and the temperature of the intersection of the third control signal and the reference control signal,
The high temperature region is set to a high temperature region from the midpoint of the temperature of the intersection of the second control signal and the reference control signal, and the temperature of the intersection of the third control signal and the reference control signal,
The normal temperature region is set to a region between the low temperature region and the high temperature region.   An oscillator comprising: a crystal resonator; and the oscillation device according to claim 1 that causes the crystal resonator to oscillate.

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