JPH0763145B2 - Digitally controlled temperature compensation oscillator - Google Patents

Description

TECHNICAL FIELD The present invention relates to a temperature-compensated oscillator that oscillates a stable frequency even when ambient temperature changes, and more particularly to a digitally controlled temperature-compensated oscillator.

〔Overview〕

The present invention, in a temperature-compensated oscillator for digitally compensating the control signal voltage of the oscillation frequency due to the ambient temperature, samples and holds two values of the analogized control signal voltage after compensation at different times. By comparing and charging and discharging by the charge and discharge circuit, and smoothing the gap between these two values, the time discontinuity of the control signal voltage generated for digitization is removed, and the oscillation due to the frequency or phase modulation is eliminated. It is intended to prevent the generation of noise in the device.

[Conventional technology]

Mobile radio devices and the like tend to have a narrow band, and local oscillators are required to have high frequency stability over a wide temperature range. A digitally controlled temperature-compensated oscillator has recently received attention as an oscillator that satisfies this requirement.

That is, as shown in FIG. 4, in the conventional temperature-compensated oscillator, the temperature information signal 101 detected by the temperature sensor 11 is converted into a first digital signal 102, which is read-only memory 2.
To output the second digital signal 201,
Analog voltage 301 by digital-analog converter 31
To the voltage controlled oscillator 32.

In such a digital control type temperature compensation oscillator, the second digital signal 201 for controlling the frequency of the voltage controlled oscillator is written in the read-only memory in advance.

Generally, the frequency control voltage of a voltage controlled oscillator varies from oscillator to oscillator. However, in the digital control type temperature compensation oscillator, the control signal voltage can be individually stored in each oscillator, so that highly accurate frequency stabilization with respect to temperature can be achieved.

In such a temperature-compensated oscillator, the ambient temperature change range is 100
It is easy to set the frequency fluctuation rate to about ± 1 to 2 ppm with respect to ° C.

[Problems to be solved by the invention]

However, in the above-described digital control type temperature compensation oscillator, the oscillation frequency discretely changes while the ambient temperature changes.

That is, the second digital signal output from the read-only memory corresponding to the information of the change in ambient temperature at times t ₀ , t ₁ , t ₂ , ... Shown in the upper part of FIG. It is converted into a value and becomes the control voltage of the oscillation frequency. When the control voltage of this oscillation frequency changes in temperature between times, this value changes discretely as shown in the middle part of FIG.

Therefore, the oscillation frequency discretely changes as shown in the lower part of FIG. When the frequency changes abruptly discontinuously in this way, frequency modulation noise or phase modulation noise occurs in the wireless device or the like, which deteriorates the communication quality.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a digital control type temperature compensated oscillation device which is capable of improving the above-mentioned drawbacks and of which change is smooth and noise is small.

[Means for solving problems]

The present invention has first and second sample and hold circuits that sample and hold the frequency control voltage output from the digital-analog converter at two different times, and compare the magnitude of the two held frequency control voltages. There is a comparator that performs voltage control by discharging or charging with the RC time constant in the charging / discharging circuit so that the first frequency control voltage matches the second frequency control voltage based on the result of comparison by the above comparator. It is characterized by having means for generating a frequency control voltage to the oscillator.

That is, according to the present invention, a temperature detecting section that detects an ambient temperature and outputs it as a digital quantity, a storage section that previously stores control output data corresponding to the digital quantity as an address input, and the control output data. A digital-analog conversion circuit for converting an analog quantity into an analog quantity, and a voltage-controlled oscillator for inputting the analog quantity converted by this circuit as a frequency control voltage. The first and second sample-and-hold circuits that sample and hold the output of each at two different times, the circuit that compares the first and second hold voltages held by these, and the comparison result of this comparing circuit The first hold voltage is brought closer to the second hold voltage based on Characterized in that a charging circuit for charging or discharging the.

[Action]

The control signal voltage, which has been temperature-compensated and analogized with respect to the ambient temperature change, has a time discontinuity when digitally converted. Hold this at different times, compare the held values one by one two by one, and if the latter value is high, charge it through the charge / discharge circuit, and if the latter value is low, discharge it through the charge / discharge circuit. Then, the fluctuation of the control signal voltage is smoothed in time and input to the voltage controlled oscillator.

〔Example〕

Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of the above embodiment.

In the figure, an oscillation including a temperature detection unit 1 including a temperature sensor 11 and an analog / digital converter 12, a read-only memory 2 (P / ROM), a digital / analog converter 31 and a voltage controlled oscillator 32 (VCO). And part 3.

The second digital signal 201 is converted into an analog voltage 301 by the digital / analog converter 31 and becomes a frequency control signal of the voltage controlled oscillator 32. The voltage controlled oscillator 32 has a crystal oscillator and a variable capacitance element.

The temperature sensor 11 outputs an analog voltage corresponding to the ambient temperature as a temperature information signal 101. The analog quantity output is converted by the analog-to-digital converter 12 into the first digital signal 102. The read-only memory 2 outputs the second digital signal 201 corresponding to this first digital signal as an address signal.

The second digital signal 201 is converted into an analog voltage 301 by the digital / analog converter 31 and becomes a frequency control signal of the voltage controlled oscillator 32.

Here, the feature of the present invention is that the output of the digital-analog converter 31 is monitored, and when the output voltage is discontinuous in time, the first sample voltage is changed to the second sample voltage. The frequency control voltage applying section 4 including a charging / discharging circuit that charges or discharges so as to match is provided between the digital / analog converter 31 and the voltage controlled oscillator 32.

The configuration and operation of the frequency control voltage applying section 4 will be described below with reference to the time chart shown in FIG.

First, the analog switch (AS-1) 403 in FIG. 1 and the capacitor 404 form a first sample-hold circuit, and the digital-analog converter is operated at the first time shown by AS-1 timing in FIG. Sample and hold the output voltage of. Similarly, the analog switch (AS-2) 405 and the capacitor 406 form a second sample and hold circuit,
The digital-analog converter output voltage is sampled and held at a second time indicated by AS-2 timing, which is an arbitrary time delay from the first time.

Next, the analog switch (AS-3) 407 and the analog switch (AS-4) 408 conduct at the timing of AS-3 and AS-4, and the comparator 409 compares the two sample voltages.

The case where the first sample voltage is lower than the second sample voltage will be described below. At this time, the waveform of the output a of the comparator rises from L to H as indicated by the symbol a in FIG. This output is waveform-shaped by the D flip-flop circuit 410 in synchronization with the rising timing of the clock. The output b of the D flip-flop circuit 410 is directly applied to one input of the exclusive OR circuit 412 and both are set to 1
It is applied to the other input (shown by the waveform c) of the exclusive OR circuit via the bit shift register (SR) 411. As a result, the output d of the exclusive OR circuit outputs a pulse of only one clock cycle as shown by symbol B in FIG. Since this output is input to the binary counter (DC) 413, its output e changes from L to H.

On the other hand, the output of the first sample hold circuit is connected to the power supply 417 via the analog switch 407, the first n-channel MOS transistor 414, the resistor 415 and the second n-channel MOS transistor 416. Further, the connection point between the resistor 415 and the second n-channel MOS transistor 416 is grounded via the p-channel MOS transistor 418. The output of the binary counter 413 is connected to the gate of the first n-channel MOS transistor 414, and the output of the comparator 409 is connected to the gates of the second n-channel MOS transistor 416 and p-channel MOS transistor 418. There is.

Therefore, when the binary counter 413 becomes L, the first n-channel MOS transistor 414 is activated. At this time, since the comparator output a is H, the second n-channel MOS transistor 416 is energized and the p-channel MOS transistor 418 is opened. As a result, the first sample voltage is charged with the RC time constant and increases continuously with respect to the second sample voltage. Here, R is the resistance
The resistance value of 415 and C are the capacitance values of the capacitance 404.

When the charging is completed and the first sample voltage becomes equal to the second sample voltage, the output of the comparator is inverted as indicated by symbol C and the output of the exclusive OR circuit is changed by 1 as indicated by symbol D.
Output the pulse again. The output of the binary counter is from H to L
, The first n-channel MOS transistor 414 is opened, and charging is stopped.

In the above, the case where the first sample voltage is lower than the second sample voltage has been described. However, the operation in the opposite case is p channel MOS transistor 416 instead of the second n channel MOS transistor 416 being energized. 418 energizes and discharges with a time constant RC, causing the first sample voltage to decrease continuously in time to the second sample voltage.

In FIG. 2, the first sample voltage is higher than the second sample voltage corresponding to each of the waveforms a, b, c, d, and e when the first sample voltage is lower than the second sample voltage. When the waveforms of the voltage change in the case are a ′, b ′,
Indicated by c ', d', and e '.

As shown in FIG. 1, the first sample voltage is applied to the voltage controlled oscillator 32 as the frequency control voltage 401,
Waveform changes of control voltage and oscillation frequency corresponding to FIG.
The waveform characteristic diagram shown in FIG. 3 is obtained. For the waveform characteristics of the oscillation frequency of FIG. 3, the example of FIG. 5 is shown by a broken line for comparison.

Since the control voltage changes continuously with time at the sampling point,
The oscillation frequency of the voltage-controlled oscillator has a characteristic that continuously changes with time as shown in the lower part of FIG. Therefore, there is no abrupt frequency change like point B shown in the lower part of FIG. Therefore, according to the present invention, frequency modulation noise and phase modulation noise are significantly reduced.

〔The invention's effect〕

As described above in detail, according to the present invention, the change in the control voltage is smooth, so that the fluctuation in the oscillation frequency is also smooth. Therefore, no step noise is generated. As a result, it is possible to obtain a digital control type temperature compensation oscillator in which the oscillation frequency is remarkably stable and the frequency modulation noise and the phase modulation noise are remarkably reduced. If this is used for a wireless device, there is an effect that good call quality can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention. FIG. 2 is a time chart explaining the operation of the above embodiment. FIG. 3 is a waveform characteristic diagram of the ambient temperature, the control voltage and the oscillation frequency in the above embodiment. FIG. 4 is a block diagram of a conventional device. FIG. 5 is a waveform characteristic diagram of an ambient temperature, a control voltage and an oscillation frequency of a conventional example. 1 ... Temperature detector, 2 ... Read-only memory (P ・ RO
M), 3 ... Oscillation section, 4 ... Frequency control voltage application section, 11
... Temperature sensor, 12 ... Analog / digital converter,
31: Digital-analog converter, 32: Voltage controlled oscillator (VCO), 33: Output terminal, 101: Temperature information signal,
102, 201 ... First and second digital signals, 301 ...
Analog voltage, 401 ... Oscillation frequency control voltage, 403 ...
Analog switch (AS-1), 404, 406 ... Capacitor, 405 ... Analog switch (AS-2), 407 ... Analog switch (AS-3), 408 ... Analog switch (A
S-4), 409 ... Comparator, 410 ... D flip-flop circuit (DFF), 411 ... 1-bit shift register (SR), 412 ... Exclusive OR circuit (Ex-OR), 413 ...
Binary counter (DC), 414, 416 ... n-channel MOS transistor, 415 ... Resistor, 417 ... Power supply, 418 ... P-channel MOS transistor, a, b, c, d, e. Output waveform, a ', b', c ', d', e '... Waveform of each output during discharge.

Claims (1)

[Claims] 1. A temperature detecting section for detecting an ambient temperature and outputting it as a digital quantity, a storage section for preliminarily storing corresponding control output data using this digital quantity as an address input, and this control output data. A digital-analog conversion circuit, comprising: a digital-analog conversion circuit for converting an analog quantity into an analog quantity; and a voltage-controlled oscillator for inputting the analog quantity converted by this circuit as a frequency control voltage. First and second sample-and-hold circuits that sample and hold the output of each at two different times, circuits that compare the first and second hold voltages held by these circuits, and the comparison results of this comparing circuit To make the first hold voltage closer to the second hold voltage based on And a charge / discharge circuit for charging or discharging the digitally controlled temperature-compensated oscillator.