JP6425581B2 - Digital temperature compensated oscillator - Google Patents

Description

  The present invention relates to a digital temperature compensated oscillator that compensates for frequency variations due to temperature changes based on digitized temperature information.

  In recent years, as mobile environments such as high-performance mobile terminals such as smartphones become small cells such as femtocells, picocells, and microcells, the requirements for the frequency stability of their base station side clocks become severe. A temperature compensated oscillator is generally used as a clock for applications requiring this high frequency stability.

  Conventionally, various temperature-compensated oscillators are known, but as the digital temperature-compensated oscillator, a temperature sensor having a large fluctuation in oscillation frequency due to temperature is used to digitally control external temperature change information detected by the temperature sensor. The digital code is made by the circuit, and the digital temperature compensation code generated by the digital temperature compensation circuit based on the temperature digital code is converted into an analog signal by the D / A converter to generate the temperature compensation voltage (frequency control voltage) There is known a configuration in which this temperature compensation voltage is input to a voltage controlled oscillator to control the oscillation frequency of the voltage controlled oscillator. The temperature compensation digital data for compensating the change of the oscillation frequency to the environmental temperature generated by the voltage controlled oscillator is correction data for canceling the change of the oscillation frequency due to the temperature drift of the voltage controlled oscillator. Conventionally, it is common to obtain by a polynomial approximation.

  However, the correction data based on this polynomial approximation does not match the original correction data to be temperature-compensated, that is, the actually measured correction data, and has a difference which can not be corrected (hereinafter referred to as residual). For example, as shown in FIG. 13, in the polynomial approximation correction data represented by a solid line approximated by a tenth-order polynomial in an environment temperature range of −40 to 100 ° C., the residual component to the correction data obtained by measurement is corrected. It is necessary to add a residual correction component represented by a dotted line which is the difference between the measured correction data and the polynomial approximation correction data. In FIG. 13, the display range of the polynomial approximation correction is ± 25,000 ppb, and the display range of the residual correction is one-tenth ± 2,500 ppb (this value is a frequency of 25 ° C. Normalized value with).

  In order to obtain this residual correction amount, while the correction data is obtained by actual measurement for every temperature interval, when the environmental temperature does not correspond to the actual correction data, it is calculated based on the actual correction data. It is common to obtain residual correction data. In the related art, as a measure for obtaining the residual correction data by calculation, a linear function is used as an approximate expression, spline interpolation using a second or higher order polynomial, or the least squares method is used. It has been proposed to use the approximate curve used (Patent Document 1).

JP, 2013-98865, A

  However, according to this conventional proposal, when using a linear function as an approximation formula, there is a disadvantage that residual correction data can not be calculated with high accuracy unless the interval to be measured is reduced. In addition, when spline interpolation using a second or higher order polynomial is used, the coefficients used for the calculation are different in each temperature section, so a large number of non-volatile memories for storing the respective coefficients are required. There is a disadvantage. For example, in the case of spline interpolation using a quadratic polynomial, if the number of temperature sections is M, the number of words in the non-volatile memory is 3 M, and in the case of spline interpolation using a cubic polynomial, 4 M is required. Then, in the case where an approximate curve using the least squares method is used, there is a disadvantage that residual correction data can not be calculated with high accuracy.

  An object of the present invention is to solve these problems and provide a digital temperature compensated oscillator capable of accurate temperature compensation over a wide temperature range.

  In order to achieve the above object, a digital temperature compensated oscillator according to claim 1 of the present invention generates an oscillation frequency (first oscillation frequency) whose frequency changes with respect to a change in environmental temperature, and at the same time by the control voltage. A voltage controlled oscillator that generates an oscillation signal capable of controlling the oscillation frequency of the second oscillation frequency; and an oscillation frequency (a second oscillation frequency) whose change rate is larger than a first oscillation frequency of the voltage controlled oscillator with respect to changes in the environmental temperature. Digital information obtained by comparing the temperature-sensitive oscillator that generates the oscillation frequency) with the first oscillation frequency generated by the voltage-controlled oscillator and the second oscillation frequency generated by the A temperature digital data generation unit for calculating based on the temperature data and generating the environmental temperature when the comparison is performed as temperature digital data; A temperature compensation circuit for generating temperature compensated digital data to compensate for a change in environmental temperature of a first oscillation frequency generated by a voltage controlled oscillator, a passive multistage low pass filter (hereinafter referred to as an LPF) comprising a ΔΣ modulator and a passive element And D / A converter configured to convert the temperature compensation digital data into the control voltage represented by an analog voltage, the temperature compensation circuit essentially including correction data to be temperature compensated and polynomial approximation The difference from the polynomial approximation correction data approximated by is used as residual correction data, and sampling is performed at a discrete temperature within the operating temperature range of the digital temperature compensated oscillator, and the sampled residual correction data is Temperature digital data stored in advance in memory and obtained from the temperature digital data generation unit The residual correction data in the temperature digital data is calculated by the digital filter based on the data and the residual correction data corresponding to four or more sampling points before and after sandwiching the temperature digital data, and the result is obtained as the temperature digital The data is added to the polynomial approximation correction data corresponding to the data to obtain temperature compensation digital data.

  In order to achieve the above object, a digital temperature compensated oscillator according to claim 2 of the present invention uses a polyphase FIR filter as the digital filter in the configuration according to claim 1, and also uses polyphase FIR filter interpolation (hereinafter referred to as The residual correction data is calculated by combining linear interpolation with FIR interpolation).

  In order to achieve the above object, a digital temperature compensated oscillator according to claim 3 of the present invention is constituted by dividing the working environment temperature range into high temperature side and low temperature side according to the configuration of the second invention, and sampling points for each part. Are sequentially set from the maximum temperature value and the minimum temperature value to the opposite side, and calculation is performed using different FIR filter interpolation formulas for each part.

  According to the digital temperature compensation oscillator according to claim 1 of the present invention, it is possible to cope with residuals which can not be coped with by temperature correction data by polynomial approximation with high accuracy, so that temperature compensation in a wide temperature range is possible. The effect of becoming

  According to the digital temperature compensated oscillator of claim 2 of the present invention, in addition to the effects of claim 1, the use of the polyphase FIR filter brings about an effect that efficient calculation can be performed on the residual component. .

  According to the digital temperature compensation oscillator of the present invention, in addition to the effects of the second aspect, one sampling point is added to each of the maximum temperature side and the minimum temperature side of the operating environment temperature range. If it is enough, there is no need to add a plurality of sampling points, so it is effective.

FIG. 1 is a block diagram showing an entire configuration of an embodiment of a digital temperature compensation oscillator according to the present invention. Similarly, a block diagram of a temperature compensation circuit. The graph which similarly shows the sampling example of residual correction data. Data No. of residual correction data sampled similarly. Schematic explanatory drawing of the look-up table which shows the correspondence with temperature. The graph which shows typically the relationship of the temperature digital data and residual correction data which were similarly output from the temperature digital generation part. Similarly, a graph schematically showing residual correction data by FIR interpolation and linear interpolation. The table which similarly shows an example of the coefficient for FIR interpolation operation. The graph which similarly shows the coefficient of FIG. The block diagram which similarly shows an example of a FIR interpolation remainder correction arithmetic circuit. A graph schematically showing an example in which two extra sampling points are required on the high temperature side. A graph schematically showing an example in which one extra sampling point is sufficient on the high temperature side. A graph schematically showing an example in which one extra sampling point is sufficient on the low temperature side. The graph which similarly shows the relationship between a polynomial approximation correction part and a residual correction part.

  First, the entire configuration of a digital temperature compensated oscillator according to the present invention will be described based on FIG. 1 of the accompanying drawings. The digital temperature compensated oscillator comprises a voltage controlled oscillator 1, a temperature sensitive oscillator 2, a temperature digital data generation unit 3, a temperature compensation circuit 4, a ΔΣ modulator 5 and a passive four-stage LPF 6 Is equipped.

  The voltage control type oscillation circuit 12 of the voltage control type oscillator 1 has a known configuration and has an externally attached vibrator 11. The voltage controlled oscillator 1 generates an oscillation frequency (first oscillation frequency) whose frequency changes in response to a change in environmental temperature, and the first oscillation frequency is controlled by the control voltage output from the passive four-stage LPF 6 An oscillation signal that can be controlled is generated. The generated oscillation signal having the first oscillation frequency is output to the buffer 8 and is input to the first counter 31 of the temperature digital data generation unit 3 through the divider circuit 9, while the oscillation signal having the first oscillation frequency is output from the buffer 8. It is output to the outside through the buffer 10.

  The temperature-sensitive oscillator 2 is a ring oscillator formed by connecting an odd number of inverters in a ring shape, and the change rate of the temperature-controlled oscillator 2 is larger than the first oscillation frequency generated by the voltage controlled oscillator 1 with respect to changes in environmental temperature. The oscillation frequency (second oscillation frequency) is generated. The generated oscillation signal having the second oscillation frequency is output to the second counter 32 of the temperature digital data generation unit 3.

  The temperature digital data generation unit 3 includes the counters 31 and 32 and a control circuit / temperature conversion circuit 33. The counters 31 and 32 are controlled by control signals of the control circuit. The counter 31 counts the first oscillation frequency generated by the voltage controlled oscillator 1, and the counter 32 counts the second oscillation frequency generated by the temperature-sensitive oscillator 2. The oscillation frequencies are compared by the control circuit / temperature conversion circuit 33, and the environmental temperature is calculated as digital data from the oscillation frequency of the temperature-sensitive oscillator 2 to generate temperature digital data. The temperature digital data is output from the control circuit / temperature conversion circuit 33 to the calculation circuit 41 of the temperature compensation circuit 4.

  The temperature compensation circuit 4 includes an arithmetic circuit 41 and a memory 42, and generates temperature compensation digital data for compensating the change of the first oscillation frequency generated by the voltage controlled oscillator 1 with respect to the environmental temperature. This temperature compensation digital data is digital data which is a correction for canceling a change in oscillation frequency due to temperature drift of the voltage control type oscillator 1, and this polynomial approximation correction data is obtained by polynomial approximation correction data to be obtained by a polynomial approximation formula. In the above, residuals remaining without correction are obtained by adding residual correction data obtained by FIR interpolation and linear interpolation.

  As shown in FIG. 2, the arithmetic circuit 41 to which the temperature digital data of the temperature compensation circuit 4 is input is a polynomial correction arithmetic circuit 41a for calculating polynomial approximation correction data, and a cascaded FIR interpolation residual for obtaining residual correction data. The polynomial approximation correction data obtained by the circuit 41a and the residual correction data obtained by the circuits 41b and 41c are composed of a difference correction calculation circuit 41b and a linear interpolation residual correction calculation circuit 41c. , And output as temperature-compensated digital data. On the other hand, the memory 42 includes a polynomial coefficient memory 42 a storing coefficients necessary for the calculation of polynomial approximation expressions, and a residual data memory 42 b storing residual data required for FIR interpolation. It comprises an FIR coefficient memory 42c in which necessary coefficients are stored.

Here, generation of temperature compensation digital data will be described in detail. For example, polynomial approximation correction data in a use environment temperature range of the voltage control type oscillator 1 in the range of -40 to 100 ° C. is a tenth-order polynomial if the target value of the error is about ± 200 ppb TC ₁₀ = A ₀ + A ₁ (T-T ₀ ) + A ₂ (T-T ₀ ) ² + A ₃ (T-T ₀ ) ³ + A ₄ (T-T ₀ ) ⁴ + A ₅ (T-T ₀ ) ⁵ + A ₆ (T- T ₀ ) ⁶ + A ₇ (T−T ₀ ) ⁷ + A ₈ (T−T ₀ ) ⁸ + A ₉ (T−T ₀ ) ⁹ + A ₁₀ (T−T ₀ ) ¹⁰ can be calculated (see FIG. 13) ). Here, TC ₁₀ is polynomial approximation correction data output from the polynomial correction operation circuit 41 a, A _{0 to} A ₁₀ are coefficients stored in advance in the polynomial coefficient memory, and (T−T ₀ ) is a control circuit / temperature conversion It is temperature digital data output from the circuit 33.

  FIG. 3 shows an example in which residual correction data (see FIG. 13) is sampled and extracted at a temperature interval of 4 ° C. The sampled residual correction data is stored in advance in the residual data memory 42b. ing. FIG. 4 shows the data No. of the residual correction data at 4 ° C. intervals. The correspondence relationship with the temperature is shown as a look-up table (hereinafter referred to as a LUT). In the residual data memory 42b, data No. 1 is stored. Is the address, and the residual correction data is stored as data. Is associated with the temperature. Note that i, n and N in FIG. 4 are all integers, the temperature interval ΔT is {T (N) −T (0)} / N, and in this example, ΔT = 4 (° C.).

  When the temperature digital data T output from the control circuit / temperature conversion circuit 33 is a temperature corresponding to the address of the residual correction data, residual correction data is stored in the residual data memory 42b. For example, when the temperature digital data T is between the temperature T (n) and the temperature T (n + 1) in the LUT of FIG. 4, it is necessary to obtain residual correction data by calculation. FIG. 5 schematically shows the relationship between temperature digital data and residual correction data shown in FIG. 4 sampled in advance, for temperature digital data in the range of T (n−3) to T (n + 3). T) is the residual correction data to be obtained.

  In the present embodiment, residual correction data y (T) shown in FIG. 5 is divided into four temperature steps T (n-1), T (n), T (n + 1) which are before and after sandwiching the temperature digital data T. On the basis of the residual correction data corresponding to T (n + 2), calculation is made by 4-phase FIR interpolation, and the result is further calculated by linear interpolation, in other words, interpolation by a linear function. More specifically, as shown in FIG. 6, three interpolation points are obtained by quartering between T (n) and T (n + 1) before and after sandwiching the temperature digital data T in FIG. 5 by FIR interpolation. Here, the data No. corresponding to the interpolation point. Is n + k / 4, temperature digital data is T (n + k / 4), residual correction data is y (n + k / 4), and k is an integer satisfying 0 <k ≦ 4. In the case of k = 4, T (n + 1) is obtained. Therefore, three interpolation points T (n + 1/4), T (n + 1/2), and T (n + 3/4) may be obtained as interpolation points.

  Then, residual correction data y (n + 1/4), y (n + 1/2), y (respectively) of these three interpolation points T (n + 1/4), T (n + 1/2), T (n + 3/4) Among n + 3/4), residual correction data of temperature digital data before and after temperature digital data T is located, and in the example of FIG. 6, residual correction data of T (n + 1/2) and T (n + 3/4) Interpolation is performed to obtain residual correction data y (T) corresponding to the temperature digital data T. Therefore, in this example, it is possible to obtain residual correction data y (T) without obtaining residual correction data corresponding to the interpolation point T (n + 1/4).

Specifically, as shown in FIG. 5, four temperature digital data T (n-1), T (n), T (two), ie, two on the low temperature side and two on the high temperature side, sandwich the temperature digital data T. Residual correction data y (n-1), y (n), y (n + 1), y (n + 2), and four-phase polyphase FIR filter coefficients c (i, j) of n + 1) and T (n + 2) The following equation is substituted for the following equation to obtain FIR interpolation data.
y (n + 1/4) = c (3,1) * y (n-1) + c (3,2) * y (n) + c (3,3) * y (n + 1) + c (3,4) * y (n + 2)
y (n + 1/2) = c (2, 1) * y (n-1) + c (2, 2) * y (n) + c (2, 3) * y (n + 1) + c (2, 4) * y (n + 2)
y (n + 3/4) = c (1,1) * y (n-1) + c (1,2) * y (n) + c (1,3) * y (n + 1) + c (1,4) * y (n + 2)
y (n + 1) = c (0,1) * y (n-1) + c (0,2) * y (n) + c (0,3) * y (n + 1) + c (0,4) * y (n + 2) )
The arithmetic expressions correspond to the FIR filter 3 (phase 3), the FIR filter 2 (phase 2), the FIR filter 1 (phase 1), and the FIR filter 0 (phase 0) in this order from the top. Further, the coefficient c (i, j) is obtained in consideration of the filter characteristics of the cut-off frequency, the pass band, and the stop band in the temperature region of the residual correction data, and in the 16-tap polyphase FIR filter, An example used for the above-mentioned arithmetic expression is shown in FIGS. 7 and 8.

  FIG. 9 calculates residual correction data y (n + 1/2) and y (n + 3/4) of the interpolation points T (n + 1/2) and T (n + 3/4) before and after the temperature digital data T described above is located An example of the circuit configuration for performing this is shown. Here, FIR filter A (phase A) and FIR filter B (phase B) indicate two FIR filters selected from FIR filters 0 to 3 (phases 0 to 3), and in this example, FIR filters 1 (phase 1) and FIR filter 2 (phase 2) correspond. When the temperature digital data T is input, the interpolation temperature position calculation circuit 411 calculates the temperature position (the position of the temperature T in FIG. 5) corresponding to the data T, and the residual data address calculation circuit 412 and the FIR coefficient address calculation circuit Output to 413. The residual data address calculation circuit 412 has data No. 1 for reading residual correction data necessary for interpolation from the residual data memory 42 b. Calculate the address corresponding to On the other hand, at the same time, the FIR coefficient address calculation circuit 413 calculates an address for reading out the FIR filter coefficients of two phases before and after the temperature position.

  Based on the results of these address calculations, the residual data memory 42b calls corresponding residual correction data y (n-1), y (n), y (n + 1), y (n + 2), The corresponding FIR coefficients of phase 1 and phase 2 are called from the memory for FIR coefficients 42c. Then, interpolation data y (n + 1/2) and y (n + 3/4) are calculated based on the above-described arithmetic expressions in two phases corresponding to these FIR coefficients, and each interpolation data y (n + 1/2) and y is calculated. The (n + 3/4) is added by the adder 416 and output to the linear interpolation residual correction operation circuit 41 c (see FIG. 2).

  The linear interpolation residual correction operation circuit 41c shown in FIG. 2 corrects the residual corresponding to the temperature digital data T by a linear approximation based on the two interpolation data y (n + 1/2) and y (n + 3/4). Data y (T) is obtained, and the residual correction data y (T) is output to the adder 41 d. Then, in the adder 41d, the polynomial approximation correction data obtained by the polynomial correction operation circuit 41a and the residual correction data y (T) are added to generate temperature compensation digital data.

  The ΔΣ modulator 5 to which the temperature compensation digital data generated by the temperature compensation circuit 4 as described above is input, as shown in FIG. 1, includes the multiplier 51, the adders 52a, 52b and 52c, and the delay circuit 53a, 53 b and 53 c, multipliers 54 a and 54 b, a quantizer 55, and a PWM modulator 56. A dither signal is input to the adder 52 b, and the dither signal is composed of data of lower bits of the output of the counter 32 which has received the output of the temperature-sensitive oscillator 2. For example, assuming that the output of the counter 32 receiving the output of the temperature sensitive oscillator 2 is 18 bits of data, it is preferable that the lower 4 bits of data be a dither signal.

  Further, the quantizer 55 is a multi-value quantizer of three or more values, and for example, a four-value PDM signal quantized at four levels of “00”, “01”, “10”, and “11” , And to the adder 52c. The PWM modulator 56 outputs a binary PWM signal with a multi-level pulse width of three or more levels. For example, if the quantizer 55 has four values (four levels), “0 Among the four pulse widths of “1”, “2” and “3”, converting to a binary PWM signal having a pulse width of a level corresponding to the level of the input PDM signal, Output to the 4-stage LPF 6. On the other hand, together with the output of the quantizer 55, a signal to be input to the adder 52b is also input to the adder 52c, and a quantization error by the quantizer 55 is output from the adder 52c.

  The delay circuits 53a, 53b, and 53c delay the quantization error by one cycle, two cycles, and three cycles. The output of the delay circuit 53a is input to the adder 52a after being multiplied by a predetermined coefficient by the multiplier 54a. The output of the delay circuit 53b is multiplied by a predetermined coefficient by a multiplier 54b and input to the adder 52a. On the other hand, the output of the delay circuit 53c is directly input to the adder 52a. The output of the multiplier 51 is input to the adder 52a in addition to these inputs, and the inputs are added and output to the adders 52b and 52c.

  The passive four-stage LPF 6 includes four stages of LPFs each including a resistive element and a capacitive element. The total resistance value of each resistance element is, for example, 1 GΩ, the resistance of the first stage is 700 MΩ, and the other three resistance elements are set to 100 MΩ. For each capacitance element, for example, the sum of capacitance values is 100 pF, the fourth-stage capacitance element at the final stage is 70 pF, and the other three capacitance elements are each set to 10 pF. There is. As described above, when the resistance value of the first stage and the capacitance value of the final stage are set larger than the other resistance values or capacitance values, the attenuation amount in the low frequency range can be increased. The PWM signal is converted to an analog signal by passing through the passive four-stage LPF 6, and this analog signal is input to the voltage controlled oscillator circuit 12 of the voltage controlled oscillator 1 as a control voltage signal.

Subsequently, the operation of the above-described digital temperature compensated oscillator will be described.
When the voltage control type oscillator 1 generates and outputs an oscillation signal of a frequency (first oscillation frequency) corresponding to the environmental temperature, the oscillation signal is output from the buffer 8 to the external device through the buffer 10, The buffer 8 is inputted to the divider circuit 9. The divider circuit 9 divides the input oscillation frequency and outputs it to the counter 31. On the other hand, the temperature-sensitive oscillator 2 generates an oscillation signal of a frequency (second oscillation frequency) whose change rate is larger than the first frequency with respect to the environmental temperature, and outputs the oscillation signal to the counter 32.

  The oscillation frequencies counted by the counters 31 and 32 are compared by the control circuit / temperature conversion circuit 33, and the control circuit / temperature conversion circuit 33 compares the digital information obtained by the comparison. The ambient temperature at that time is generated as temperature digital data, and this temperature digital data is output to the arithmetic circuit 41.

  The arithmetic circuit 41 including the polynomial correction arithmetic circuit 41a, the FIR interpolation residual correction arithmetic circuit 41b, and the linear interpolation residual arithmetic circuit 41c obtains the polynomial coefficient memory 42a and the residual from the input temperature digital data as described above. Calculation is performed based on each arithmetic expression, data and coefficient value stored in the memory 42 including the difference data memory 42 b and the memory for FIR coefficient to compensate for the change of the oscillation frequency of the voltage control type oscillation circuit 12 with respect to the environmental temperature Temperature compensation digital data is output to the .DELTA..SIGMA.

  The temperature compensated digital data input to the ΔΣ modulator 5 is converted to a four-level (four-level) PDM signal by the quantizer 55, and further converted to a binary PWM signal with a four-level pulse width by the PWM modulator 56. Be done. Then, the PWM signal is converted into an analog signal by the passive four-stage LPF 6 to convert the temperature compensation digital data into a control voltage represented by an analog voltage and input the voltage control oscillation circuit 12 to the voltage control. The oscillation frequency of the oscillator 1 is controlled.

  In the above embodiment, since the use environment temperature range of −40 ° C. to 100 ° C. is sampled at 4 ° C. intervals which is a divisor of 140, from the lowest temperature value of −40 ° C. to the high temperature side of the use environment temperature range. Even if the sampling points are sequentially determined or the sampling points are sequentially determined from the maximum temperature value of 100 ° C. toward the low temperature side, both temperature values become sampling points. Therefore, when the temperature digital data T is between the lowest temperature value or the highest temperature value and the sampling point immediately before that, the temperature data T is supported by FIR interpolation using four residual correction values before and after In order to obtain residual correction data to be corrected, it is sufficient for the low temperature side and the high temperature side to have a sampling point one ahead of the operating environment temperature range. That is, in FIG. 5, if T (n + 1) is the maximum temperature value, T (n + 2) is sufficient on the high temperature side, and T (n + 3) or more is unnecessary. If T (n) is the lowest temperature value, T (n-1) is sufficient on the low temperature side, and T (n-2) or less is unnecessary.

  However, when sampling the use environment temperature range of -40 ° C to 100 ° C at intervals of 3 ° C or 8 ° C not a divisor of 140, the sampling point is -40 ° C, which is the lowest temperature value of the use environment temperature range. Then, on the high temperature side, the sampling point is 98 ° C. for 3 ° C. intervals and 96 ° C. for 8 ° C. intervals, and the maximum temperature value of 100 ° C. is not a sampling point (see FIG. 10). Conversely, if the sampling point is 100 ° C, which is the maximum temperature value in the operating environment temperature range, -38 ° C at 3 ° C intervals on the low temperature side and -36 ° C at 8 ° C intervals are the lowest temperature sampling points, The lowest temperature of -40 ° C does not become the sampling point.

  Therefore, for example, as shown in FIG. 10, when the temperature digital data T is between the maximum temperature value of the operating environment temperature range which is not the sampling point and the sampling point T (n) one before that, In order to obtain residual correction data corresponding to temperature data T by FIR interpolation using residual correction data, sampling points T (n + 1) and T (n + 2) up to two points after the maximum temperature value are required. . Therefore, it is necessary to set an extra sampling point and obtain residual correction data from the actual measurement. In the above example, if the lowest temperature value is the sampling point, the range of -43 ° C to 104 ° C at 3 ° C interval Also, since the range of −46 ° C. to 112 ° C. is an actual measurement range at an interval of 8 ° C., there is a disadvantage that the actual measurement temperature range is expanded more than necessary.

  In order to solve this problem, the lowest temperature value and the highest temperature value are used as sampling points, and sampling points are determined from the sampling points toward the opposite side at a predetermined temperature interval, and it is possible to If the operating environment temperature range is -40 ° C to 100 ° C, they cross each other at around 25 ° C. For example, two sampling points on one side are provided from the center to the other side, and the sampling points on the other side are One is provided from the center to one side. Then, on the high temperature side shown in FIG. 11, the interpolation data 0 equal to the residual correction data y (n + 1) is an equation corresponding to the FIR filter 0 (phase 0) using the above-described equation. The equation corresponding to (phase 1), the interpolation data 2 can be obtained by the equation corresponding to the FIR filter 2 (phase 2), and the interpolation data 3 can be obtained by the equation corresponding to the FIR filter 3 (phase 3).

On the other hand, on the low temperature side shown in FIG. 12, calculation is performed using the following operation equation different from the above-described operation equation.
y (n + 1) = c (0,4) * y (n-1) + c (0,3) * y (n) + c (0,2) * y (n + 1) + c (0,1) * y (n + 2) )
y (n + 1/4) = c (1,4) * y (n-1) + c (1,3) * y (n) + c (1,2) * y (n + 1) + c (1,1) * y (n + 2)
y (n + 1/2) = c (2, 4) * y (n-1) + c (2, 3) * y (n) + c (2, 2) * y (n + 1) + c (2, 1) * y (n + 2)
y (n + 3/4) = c (3, 4) * y (n-1) + c (3, 3) * y (n) + c (3, 2) * y (n + 1) + c (3, 1) * y (n + 2)
In this arithmetic expression, an FIR filter 0 (phase 0) for obtaining interpolation data 0 equal to residual correction data y (n), an FIR filter 1 for obtaining interpolation data 1 (phase 1), and interpolation data 2 are calculated in order from the top The FIR filter 2 (phase 2) and the FIR filter 3 for obtaining the interpolation data 3 (phase 3) correspond to each other. The coefficients c (i, j) may be those shown in FIG. 7 and FIG.
Note that T (n + 1) is the highest temperature value in FIG. 11 and T (n) is the lowest temperature value in FIG. 12 due to the relationship with each arithmetic expression.

  As described above, in the above-described embodiment, both the highest temperature value and the lowest temperature value are sampling points, and the high temperature side computing equation and the low temperature side computing equation reverse the order of the coefficients of each phase, and By using a different equation in which the order corresponding to phases 1 to 3 is reversed, temperature digital data T is the maximum temperature value in the operating environment temperature range, or the lowest temperature value and the sampling point T (n) one before that Even if there is an interval, when obtaining residual correction data corresponding to temperature data T by FIR interpolation using four residual correction data before and after, an extra necessary sampling point outside the operating environment temperature range is also on the high temperature side Even one on the cold side is enough.

The present invention is not limited to the above-described embodiment. For example, sampling points of residual correction data used for calculation with a digital filter are not limited to four before and after sandwiching temperature digital data. Further, the polynomial for obtaining the polynomial approximation correction data is not limited to the 10th order, but may be a 7th to 9th polynomial, for example.
Furthermore, the coefficients used in the FIR interpolation equation are not limited to those described above. Furthermore, when using different arithmetic expressions on the high temperature side and the low temperature side, the position dividing the operating environment temperature range is not limited to the central portion.

Reference Signs List 1 voltage control type oscillator 2 temperature-sensitive oscillator 3 temperature digital data generation unit 4 temperature compensation circuit 5 ΔΣ modulator 6 passive four-stage LPF
7 D / A converter 11 oscillator 12 voltage control type oscillation circuit 31, 32 counter 33 control circuit / temperature conversion circuit 41 arithmetic circuit 41a polynomial correction arithmetic circuit 41b FIR interpolation residual correction arithmetic circuit 41c linear interpolation residual correction arithmetic circuit 41d Adder 42 Memory 42a Polynomial coefficient memory 42b Residual data memory 42c FIR coefficient memory 51 Multipliers 52a, 52b, 52c Adders 53a, 53b, 53c Delay circuits 54a, 54b Multiplier 55 Quantizer 56 PWM modulation Unit 411 Interpolation temperature position calculation circuit 412 Residual data address calculation circuit 413 FIR coefficient address calculation circuit 414 FIR filter A operation circuit 415 FIR filter B operation circuit 416 Adder

Claims (3)

A voltage controlled oscillator that generates an oscillation frequency (first oscillation frequency) whose frequency changes in response to a change in environmental temperature and generates an oscillation signal whose control of the first oscillation frequency is possible by a control voltage;
A temperature-sensitive oscillator that generates an oscillation frequency (second oscillation frequency) whose change rate is larger than a first oscillation frequency of the voltage controlled oscillator with respect to a change in the environmental temperature;
The comparison is performed based on digital information obtained by comparing the first oscillation frequency generated by the voltage controlled oscillator with the second oscillation frequency generated by the temperature-sensitive oscillator. A digital temperature data generation unit for generating the ambient temperature at the same time as digital temperature data;
A temperature compensation circuit for generating temperature compensated digital data for compensating a change with respect to the environmental temperature of the first oscillation frequency generated by the voltage controlled oscillator based on the temperature digital data;
A digital multi-stage low pass filter comprising a Δ 多 段 modulator and a passive element, and D / A converter for converting the temperature compensated digital data into the control voltage represented by an analog voltage;
The temperature compensation circuit takes the difference between the correction data originally to be temperature-compensated and the polynomial approximation correction data approximated by polynomial approximation as residual correction data, and performs sampling at discrete temperatures within the operating temperature range of the digital temperature compensation oscillator. Based on the temperature digital data obtained from the temperature digital data generation unit and residual correction data corresponding to four or more sampling points before and after sandwiching the temperature digital data, they are extracted and stored in a memory in advance. Digital temperature compensation characterized in that residual correction data in the temperature digital data is calculated by a digital filter, and the result is added to the polynomial approximation correction data corresponding to the temperature digital data to obtain temperature compensation digital data. Oscillator.   2. The digital temperature compensated oscillator according to claim 1, wherein a polyphase FIR filter is used as the digital filter in the temperature compensation circuit, and linear interpolation is combined with the polyphase FIR filter interpolation to calculate residual correction data. The operating environment temperature range is divided into high temperature side and low temperature side, sampling points are set sequentially from the maximum temperature value and the minimum temperature value to the opposite side for each part, and calculation is performed using different FIR filter interpolation formulas for each part A digital temperature compensated oscillator as claimed in claim 2, characterized in that:

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