JPH07154138A - Digital temperature compensation oscillator - Google Patents

Abstract

PURPOSE:To make responsiveness and stability of temperature compensation control compatible with each other. CONSTITUTION:An analog signal generating circuit 21 of a D/A converter circuit 20 generates a PWM signal corresponding to temperature compensation digital value for a predetermined period. Upon the receipt of a PWM signal pulse, a 1st peak hold circuit 22 is charged by using the PWM signal as a power to hold a peak of a charged voltage. When a succeeding pulse is received, the circuit 22 is discharged. The charging, peak holding and the discharge are repeated alternately. A 2nd peak hold circuit 23 repeats alternately the charging of the PWM signal, peak holding and the discharge and its timing is reverse to that of the 1st peak hold circuit 22. A switch circuit 24 selects an output voltage of the 1st peak hold circuit 22 or an output voltage of the 2nd peak hold circuit 23 which is in holding and provides an output to a voltage controlled crystal oscillation circuit 30 as a temperature compensation analog voltage. Thus, the highly accurate digital temperature compensation oscillator is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital temperature-compensated oscillator, and more particularly to a digital temperature-compensated oscillator capable of achieving both the response and stability of temperature compensation control.

[0002]

2. Description of the Related Art FIG. 7 is a block diagram of an example of a conventional digital temperature compensation oscillator. The digital temperature compensation oscillator 500 includes a temperature compensation data generation circuit 10 and a D /
It is composed of an A conversion circuit 50 and a voltage controlled crystal oscillation circuit 30.

The temperature compensation data generation circuit 10 detects a temperature by a temperature sensor 11, and the temperature is detected by the A / D converter 1.
Converted to digital value by 2 and input to MPU13,
The MPU 13 reads the temperature compensation data corresponding to the digitally converted temperature data from the memory 14 and outputs it as a temperature compensation digital value.

The D / A conversion circuit 50 uses the PWM circuit 21 to generate a rectangular wave having a constant period, a constant amplitude, and a pulse width according to the temperature compensation digital value, and the rectangular wave is LPF. It is smoothed by the circuit 52 and output as a temperature-compensated analog voltage.

The voltage-controlled crystal oscillation circuit 30 causes an output frequency variation due to a temperature variation of the crystal oscillator, but the output frequency is controlled by the temperature-compensated analog voltage so as to cancel the output frequency variation. Maintains a constant output frequency that is not affected by temperature fluctuations.

[0006]

In the above conventional digital temperature compensation oscillator 500, the D / A conversion circuit 50 smoothes a rectangular wave to obtain a temperature compensation analog voltage. However, it is difficult to set the time constant of the LPF circuit 52,
There is a problem that it is difficult to achieve both the responsiveness and the stability of the temperature compensation control. That is, when the time constant of the LPF circuit 52 with respect to the period τ of the rectangular wave is reduced, the response is improved, but as shown in FIG. It changes with the wave period τ. On the other hand, the LPF for the period τ of the rectangular wave
When the time constant of the circuit 52 is increased, the stability is improved, but as shown by the solid line in FIG. 9, the response of the temperature-compensated analog voltage is deteriorated (the dotted line shows the case where the response is good).
When the temperature fluctuates rapidly, the output frequency fluctuates. Therefore, an object of the present invention is to provide a digital temperature-compensated oscillator that can achieve both the response and stability of temperature compensation control.

[0007]

A digital temperature compensation oscillator according to the present invention includes a temperature compensation data generating circuit for generating temperature compensation data of a digital value at a predetermined cycle based on a temperature change sensed by a temperature sensor, and the digital value. In a digital temperature compensation oscillator having a D / A conversion circuit for converting the temperature compensation data of 1 to an analog amount of the temperature compensation signal and an oscillation circuit whose output frequency is controlled by the temperature compensation signal, the D / A conversion circuit comprises: An analog signal generation circuit for generating an analog signal of an amplitude-time product according to a digital value of the temperature compensation data for each predetermined period,
A first peak that alternately repeats charging, peak holding, and discharging of the analog signal every predetermined period.
A hold circuit; a second peak and hold circuit that alternately repeats charging and peak holding and discharging of the analog signal at a timing opposite to the charging and discharging timing of the first peak and hold circuit; The peak of
And a switch circuit for alternately selecting a held one of the output voltage of the hold circuit and the output voltage of the second peak hold circuit and outputting the selected voltage as the temperature compensation signal. To do.

In the above structure, a time division type D / A converter such as a PWM circuit or a PAM circuit or an integrating type D / A converter can be used as the analog signal generating circuit.

[0009]

In the digital temperature compensation oscillator of the present invention, D
In the A / A conversion circuit, an analog signal generation circuit generates an analog signal of an amplitude-time product according to a digital value of the temperature compensation data in a predetermined cycle, and a first peak hold circuit and a second peak hold circuit. To enter. When the analog signal is input, the first peak hold circuit charges the analog signal as a power source and performs peak hold of the charging voltage. Then, when an analog signal is next input, discharging is performed. In this way, the charging and peak-holding of the analog signal and the discharging thereof are alternately repeated with the input of the analog signal as a trigger. on the other hand,
The second peak hold circuit also alternately repeats charging and peak holding of the analog signal and discharging thereof, triggered by the input of the analog signal. However, the timing is opposite to that of the first peak hold circuit. Then, the switch circuit selects a stable one of the hold voltage of the first peak hold circuit and the hold voltage of the second peak hold circuit and outputs it as a temperature compensation signal.

By decreasing the charging time constant of the peak hold circuit with respect to the analog signal generation period τ, the response is improved. However, due to the reason explained in the prior art, the stability becomes poor with only one peak hold circuit. However, since two peak hold circuits that operate at opposite timings are used and a stable hold voltage is selected and output, the temperature compensation signal is apparently stable. Therefore, both the responsiveness and the stability of the temperature compensation control can be achieved.

[0011]

The present invention will be described in more detail with reference to the embodiments shown in the drawings. The present invention is not limited to this. FIG. 1 is a block diagram of an embodiment of the digital temperature compensation oscillator of the present invention. The digital temperature compensation oscillator 100 is composed of a temperature compensation data generation circuit 10, a D / A conversion circuit 20, and a voltage controlled crystal oscillation circuit 30.

The temperature compensation data generation circuit 10 detects the temperature by the temperature sensor 11, and detects the temperature from the A / D converter 1.
Converted to digital value by 2 and input to MPU13,
The MPU 13 reads the temperature compensation data corresponding to the digitally converted temperature data from the memory 14 and outputs it as a temperature compensation digital value.

The D / A conversion circuit 20 has an analog signal generation circuit 21 for generating an analog signal of an amplitude-time product corresponding to the temperature-compensated digital value in a predetermined cycle, and an input analog signal as a power source for charging and peaking. A first peak and hold circuit 22 that repeats holding and discharging when an analog signal is input next;
A second peak and hold circuit 23 that repeats the charging, the peak and hold, and the discharge at the timing opposite to that of the first peak and hold circuit 22, and the first peak and hold circuit 23.
Hold voltage of the peak hold circuit 22 and the second
Switch circuit 24 which selects a stable one of the hold voltages of the peak hold circuit 23 and outputs it as a temperature-compensated analog voltage, the first peak hold circuit 22, the second peak hold circuit 23 and the switch. And a control circuit 25 for controlling the operation of the circuit 24.

The voltage-controlled crystal oscillator circuit 30 has its output frequency controlled by the temperature-compensated analog voltage so as to cancel the output frequency fluctuation due to the temperature fluctuation of the crystal oscillator.

FIG. 2 is a detailed circuit example of the D / A conversion circuit 20. The analog signal generation circuit 21 is configured by the PWM circuit 21. The first peak hold circuit 22 includes an AND circuit G1, a charging resistor R1, a diode D1, a capacitor C1, and a discharging transistor T1.
1 and 1. Second peak hold circuit 2
3 is an AND circuit G2, a charging resistor R2, a diode D2, a capacitor C2, and a discharging transistor T2.
Composed of and. The switch circuit 24 is composed of two analog switches AS1 and AS2. The control circuit 25 includes two flip-flops 251, 256,
It is composed of two NOT circuits 252 and 255 and two AND circuits 253 and 254.

Next, the operation of the D / A conversion circuit will be described. First, the analog signal generation circuit 21 generates a rectangular wave PWM having a constant period τ, a constant amplitude A, and a pulse width W according to the temperature compensation digital value, as shown in FIG. The flip-flop 251 is connected so as to invert the output according to the clock signal, and has a rectangular wave PW.
Since M is input as the clock signal, the FF signals 1Q and not1Q are output as shown in (a) and (c) of FIG.

The rectangular wave PWM and the FF signal 1Q are input to the AND circuit G1. Therefore, the AND circuit G1
Outputs a pulse skipping one square wave PWM, as shown in FIG. This pulse charges the capacitor C1 via the resistor R1 and the diode D1. The rectangular wave PWM and the FF signal not1Q are input to the AND circuit G2. Therefore, the AND circuit G2 outputs, as shown in (e) of FIG. This pulse has an opposite phase to that in FIG. Then, this pulse charges the capacitor C2 via the resistor R2 and the diode D2.

The NOT circuit 252 outputs an inverted rectangular wave notPWM obtained by inverting the rectangular wave PWM, as shown in FIG.

The AND circuit 253 has an inverted rectangular wave notP
The WM and FF signals not1Q are input. So A
3, the ND circuit 253 is L from the rising edge of the pulse in FIG. 3 to the falling edge of the pulse in FIG. 3E, and from the falling edge of the pulse in FIG. The H pulse is output until the rising edge of the pulse. When this pulse is L, the discharge transistor T1 is turned off, and when it is H, the discharge transistor T1 is turned on. Therefore, the discharging transistor T1 is off from the start of charging the capacitor C1 to the end of charging the capacitor C2. Further, it is on from the end of charging the capacitor C1 to the start of charging the capacitor C2, and the capacitor C1 is in the meantime.
To discharge. Therefore, the voltage V1 of the capacitor C1 is
It changes as shown in FIG.

The AND circuit 254 has an inverted rectangular wave notP
The WM and FF signal 1Q are input. So AND
As shown in FIG. 3C, the circuit 254 is at H level from the falling edge of the pulse shown in FIG. 3D to the rising edge of the pulse shown in FIG.
Then, the pulse of L is output from the rise of the pulse of E in FIG. 3 to the fall of the pulse of D in FIG. This pulse is
When it is H, the discharging transistor T2 is turned on, and when it is L, the discharging transistor T2 is turned off. Therefore, the discharging transistor T2 is off from the start of charging the capacitor C2 to the end of charging the capacitor C1. Also,
From the end of charging the capacitor C2 to the start of charging the capacitor C1, it is on, and the capacitor C2 is discharged during this period. Therefore, the voltage V2 of the capacitor C2 is
(B) changes.

The NOT circuit 255 outputs a pulse obtained by inverting the pulse shown in FIG. 3 as shown in FIG.

The flip-flop 256 is connected so that it is cleared by the L of the pulse of FIG. 3 and becomes H by the rising of the pulse of K of FIG. 3, so as shown in FIGS. , FF signals 2Q and not2Q are output. The analog switch AS1 is turned on when the FF signal 2Q is H, and turned off when the FF signal 2Q is L. The analog switch AS2 is turned on when the FF signal not2Q is H, and L
It turns off when. Therefore, the temperature-compensated analog voltage is
As indicated by the thick line in (c) of FIG. 4, the stable voltage V1 or V2 is selected as the voltage signal.

According to the digital temperature compensation oscillator 100 described above, the time constants (R1 * C1, R2 * C2) of the peak hold circuits 22 and 23 with respect to the period τ of the rectangular wave PWM.
Can be reduced to obtain good response, and the voltage V
Good stability can be obtained because the stable one of V1 and V2 is selected and output. That is, as shown in FIG. 5, the temperature-compensated analog voltage does not fluctuate in the period τ of the rectangular wave, and as shown in FIG. 6, the response of the temperature-compensated analog voltage does not change even when the temperature fluctuates rapidly. Well, the output frequency is
It will always be constant.

[0024]

According to the digital temperature-compensated oscillator of the present invention, both the response and stability of temperature compensation control can be achieved. Therefore, a highly accurate digital temperature compensation oscillator can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a digital temperature compensation oscillator of the present invention.

FIG. 2 is a detailed circuit diagram of a D / A conversion circuit of the digital temperature compensation oscillator of FIG.

FIG. 3 is a waveform diagram of each part of the D / A conversion circuit of FIG.

FIG. 4 is an explanatory diagram of a relationship between a hold voltage and a temperature compensation analog voltage.

FIG. 5 is a graph showing changes in the temperature-compensated analog voltage and the output frequency according to the present invention, which are observed in a short period such as a cycle of inputting a temperature-compensated digital value.

FIG. 6 is a graph showing changes in the temperature-compensated analog voltage and the output frequency according to the present invention, which are observed in a period sufficiently longer than the input cycle of the temperature-compensated digital value.

FIG. 7 is a block diagram of an example of a conventional digital temperature compensation oscillator.

FIG. 8 is a graph of changes in a conventional temperature-compensated analog voltage and output frequency observed in a short period of time about the input cycle of a temperature-compensated digital value.

FIG. 9 is a graph showing changes in the conventional temperature-compensated analog voltage and the output frequency observed in a period sufficiently longer than the input cycle of the temperature-compensated digital value.

[Explanation of symbols]

 100 Digital Temperature Compensation Oscillator 10 Temperature Compensation Data Generation Circuit 20 D / A Conversion Circuit 21 Analog Signal Generation Circuit 22 First Peak Hold Circuit 23 Second Peak Hold Circuit 24 Switch Circuit 25 Control Circuit 30 Voltage Control Crystal Oscillation Circuit

Claims (1)

[Claims] 1. A temperature compensation data generation circuit for generating digital value temperature compensation data at a predetermined cycle based on a temperature change sensed by a temperature sensor, and converting the digital value temperature compensation data into an analog amount temperature compensation signal. Do D
In a digital temperature compensation oscillator having an A / A conversion circuit and an oscillation circuit whose output frequency is controlled by the temperature compensation signal, the D / A conversion circuit has an amplitude / time product corresponding to a digital value of the temperature compensation data. An analog signal generation circuit for generating the analog signal every predetermined period, a first peak hold circuit that alternately repeats charging, peak hold and discharge of the analog signal every predetermined period, and a first peak hold circuit A second peak and hold circuit that alternately repeats charging and peak holding and discharging of the analog signal at a timing opposite to the charging and discharging timing of the peak and hold circuit, and the output voltage of the first peak and hold circuit. And one of the output voltages of the second peak-hold circuit that is held is alternately selected to select the temperature compensation signal. A digital temperature-compensated oscillator comprising a switch circuit for outputting as a signal.