JP2001223530A - Digital temperature compensated oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital temperature compensated oscillator that reduces noise and obtains stable oscillation frequency. SOLUTION: In this temperature compensated oscillator 1 provided with a temperature sensor 6 generating a detection voltage responding to temperature, an A/D converter 7 converting the detection voltage into a digital value, a storage circuit 8 having data for compensating the frequency temperature characteristic of a crystal oscillator in response to the digital value, a D/A converter 9 converting the data into a compensation voltage of an analog value and a clock source 10 synchronously operating the converter 7, the circuit 8 and the converter 9, the operation of the source 10 is stopped just after power is supplied. An inverter 13 having an interacting circuit consisting of a resistor 12 and a capacitor 11 on the input side is provided between a power source terminal of the source 10 and a main power source.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a temperature compensation voltage generator (hereinafter referred to as a compensation voltage generator) and a digital temperature compensation oscillator (hereinafter referred to as a temperature compensation oscillator) using the same, as an industrial technical field, and particularly to a method for consuming the same. The present invention relates to an intermittent temperature compensated oscillator with reduced power.

BACKGROUND OF THE INVENTION A temperature-compensated oscillator is used as a frequency source for a mobile phone used in a dynamic environment, for example, for compensating an oscillation frequency that changes depending on temperature. In recent years, the oscillator is operated intermittently during periods other than the talk time to reduce power consumption.

FIG. 3 is a schematic block diagram of a temperature-compensated oscillator for explaining a conventional example. The temperature-compensated oscillator includes a temperature-compensated mechanism 1 as a compensation voltage generating circuit provided in a voltage-controlled oscillator 2. Voltage controlled oscillator 2
Is obtained by inserting a voltage variable capacitance element 5 into a Colpitts-type oscillation circuit 4 using the crystal resonator 3 as an inductor component. In short, the voltage variable capacitance element 5 is inserted in the oscillation closed loop. The temperature compensating mechanism 1 includes a temperature sensor 6, A
It comprises a / D converter 7, a storage circuit 8, a D / A converter 9, and a clock source 10.

A temperature sensor 6 generates a detection voltage in response to an ambient temperature. The A / D converter 7 changes the detection voltage to a digital value. The storage circuit 8 stores a digital temperature compensation voltage in response to a temperature (detection voltage) at each address in advance. Then, an address is designated by the digital value of the detection voltage. The D / A converter 9 converts the digital temperature compensation voltage into an analog value and applies the analog value to the voltage variable capacitance element 5. The clock source 10 includes a crystal oscillator or the like, and operates the A / D converter 7, the storage circuit 8, and the D / A converter 9 in synchronization.

In such a device, the oscillation frequency that changes due to the frequency-temperature characteristic of a cubic curve having an inflection point in the vicinity of room temperature, for example, due to the crystal resonator 3 is flattened to compensate for the temperature. That is, the capacitance of the voltage variable capacitance element 5 changes according to the temperature compensation voltage.
Equivalent series capacitance of oscillation closed loop (so-called load capacitance)
Changes.

Therefore, the temperature can be digitally compensated by holding the temperature compensation voltage corresponding to the temperature for compensating the frequency temperature characteristic in the storage circuit 8 in advance. In recent years, in order to save power consumption, an intermittent system in which the power supply of the oscillator is periodically turned on and off even when the main power supply is in the ON state is employed (FIG. 4). That is, if the signal is received when the power supply of the oscillator is ON (during operation), the ON state is continued thereafter until the communication ends.

[0007]

[Problems to be Solved by the Invention]
However, the temperature-compensated oscillator having the above-described configuration has a problem in that noise is generated because the frequency change during temperature compensation rapidly changes digitally, that is, stepwise. For this reason, a system has been proposed in which the temperature is compensated after the power supply of the crystal oscillator is turned on, and thereafter the frequency fluctuation is prevented by AFC (automatic frequency control) (see Japanese Patent Application Laid-Open No. 10-16375).
No. 1). That is, during the operation of the AFC, the constant compensation voltage from the storage circuit 8 is maintained by the latch signal, and the temperature compensation operation is stopped.

The AFC receives a reference frequency from a base station, for example, and corrects the difference by applying a frequency difference from the oscillation frequency to the voltage variable capacitance element 5. However, in this case, only the compensation voltage is held by an external latch signal, and thereafter, the digital temperature compensation operation by the clock signal is repeated. Therefore, there is a problem that the digital operation interferes with the compensation voltage and still generates noise.

In Japanese Patent Application Laid-Open No. H11-27178, 1 m immediately before reception waiting during each intermittent operation when the oscillator is turned on.
It proposes temperature compensation by s. However, in such a device, temperature compensation is repeatedly performed during each intermittent operation of the oscillator, so that it has been difficult to eliminate generation of noise.

(Object of the Invention) It is an object of the present invention to provide a temperature-compensated oscillator that obtains a stable oscillation frequency with reduced noise.

[0011]

According to the present invention, the operation of the clock source for synchronizing the operations of the A / D converter 7, the storage circuit 8, and the D / A converter 9 is stopped immediately after the power of the crystal oscillator is turned on. That is the basic solution.

[0012]

According to the present invention, since the operation of the clock signal is stopped immediately after the power is turned on, the temperature compensation operation is performed only immediately after the power is turned on. After that, the oscillation frequency can be controlled by, for example, AFC. Hereinafter, an embodiment of the present invention will be described.

[0013]

FIG. 1 is a block diagram of a temperature-compensated oscillator for explaining an embodiment of the present invention. The same parts as those in the prior art are denoted by the same reference numerals, and description thereof will be simplified or omitted. As described above, the temperature-compensated oscillator includes the voltage-controlled oscillator 2 having the voltage variable capacitance element 5 in the oscillation closed loop,
The temperature compensating unit 1 includes a temperature sensor 6, an A / D converter 7, a storage circuit 8, a D / A converter 9, and a clock source 10. In this embodiment, the clock source 10
A clock stop device is inserted between the power supply terminal of the power supply and the power supply for intermittently operating the temperature compensated oscillator. The clock stop device includes an inverter 13 having an integration circuit including a capacitor 11 and a resistor 12 on an input side. The voltage variable capacitance element 5 has, for example, a temperature compensation voltage applied to the anode side and A
The FC control voltage Va is applied to the anode side as a reverse voltage.

In this case, as shown in the time charts (a to e) of FIG. 2, when the power is turned on (a in FIG. 2), the temperature compensation oscillator (temperature compensation mechanism 1) is turned on. While operating, the clock source 10 stops immediately after being turned on due to the time constant of the CR of the integration circuit (FIG. 2B).
That is, the input voltage of the inverter 13 is delayed by the integration circuit, and increases to the power supply voltage with time. Therefore, when the threshold voltage of the inverter 13 is exceeded, the power of the clock source 10 is turned off.

Therefore, the temperature compensation operation is performed only for a short period of time, for example, 1 ms before the oscillation is stabilized after the power supply of the intermittent operation is turned on, and thereafter, the digital compensation operation is stopped. That is, the temperature compensating operation is performed based on a clock pulse generated from the clock source in a short time when the power is turned on (FIG. 3C). Then, a compensation voltage responsive to the ambient temperature (supposed to be a specific temperature) is applied to the voltage variable capacitance element 5, and thereafter, the compensation voltage at the specific temperature is applied until the end of the intermittent operation (d in the figure).

Therefore, the digital operation of the temperature compensating mechanism is performed only immediately after the power is turned on for each intermittent operation, so that generation of noise can be prevented. Further, since the temperature compensation voltage is determined and applied to the voltage variable capacitance element 5 before the oscillation is stabilized after the power is turned on, the oscillation frequency is already temperature-compensated when the oscillation is stabilized. Therefore, the amount of frequency change by AFC is reduced, and AFC control is facilitated.

Since the frequency control by the AFC takes a long time to start, the frequency control is initially performed by the temperature compensation mechanism. Also, if the frequency difference from the transmission frequency from the base station is large, the AFC will not function, so the frequency difference needs to be reduced.

[0018]

Second Embodiment FIG. 3 is a schematic block diagram of a temperature compensated oscillator for explaining a second embodiment of the present invention. Note that the first
The description of the same parts as in the embodiment is omitted or simplified. In the second embodiment, the temperature compensating mechanism 1 includes a temperature sensor 6, a comparator 1
4, A / D converter 7, counter 15, control mechanism 16,
It comprises a storage circuit 8, a D / A converter 9, and a clock source (not shown). The comparator 14 inputs the detection voltage of the temperature sensor 6 to one end. The counter 15 counts the output from the comparator 14 and inputs it to the other end of the comparator 14 via the D / A converter 9. Further, the output from the counter 15 is sent to the storage circuit 8, and the address of the compensation voltage data is specified. When the detected voltage and the count signal match, the control mechanism 16
The compensation voltage data based on the count signal is output from the storage circuit 8 to the D / A converter 9. At the same time, the clock source 10 that generates the clock signal is stopped.

In such a case, as shown in the time chart of FIG. 4 (a) to (e), when the power supply of the oscillator is turned on (same as a), the clock source operates to generate the clock signal. Occur (b). Further, a detection voltage of the temperature sensor 6 (same as C) is input to one end of the comparator 14. Then, the comparator operates until the counter signal reaches the detection voltage.
An N signal (one level, the same signal E) is output. When the counter signal matches the detection voltage, an OFF signal (0 level)
Is output. The control mechanism outputs the compensation voltage data from the storage circuit and stops the clock source in response to the OFF signal as described above.

With such a configuration, the time (1) immediately after the power is turned on until the detection voltage matches the count signal is reached.
ms), and thereafter the temperature compensation operation is stopped by stopping the clock source 10. Therefore, the digital operation of the temperature compensating mechanism is performed only immediately after the power is turned on for each intermittent operation as in the first embodiment, so that generation of noise can be prevented. Since the temperature compensation voltage is set before the frequency is stabilized, the frequency control by AFC is facilitated.

[0021]

[Other Matters] In the above embodiment, the control voltage of the AFC is applied. However, when the talk time is short in a mobile phone, for example, there is no rapid temperature change, so that it is not always necessary. Also,
Although the operation is intermittent, in the case of non-intermittent operation, the temperature is compensated only immediately after the power is turned on, and then the frequency is controlled by AFC, so that noise due to the digital temperature compensation operation can be ignored.

According to the present invention, the operation of the clock source for synchronizing the operations of the A / D converter, the storage circuit and the D / A converter of the temperature assurance mechanism is stopped immediately after the power of the crystal oscillator is turned on. Therefore, it is possible to provide a temperature-compensated oscillator that obtains a stable oscillation frequency while reducing noise.

[0023]

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of a temperature compensated oscillator illustrating a first embodiment of the present invention.

FIG. 2 is a time chart of the temperature-compensated oscillator explaining the first embodiment of the present invention.

FIG. 3 is a schematic block diagram of a temperature compensated oscillator illustrating a second embodiment of the present invention.

FIG. 4 is a time chart of a temperature-compensated oscillator explaining a second embodiment of the present invention.

FIG. 5 is a schematic block diagram of a temperature compensated oscillator explaining a conventional example.

FIG. 6 is a time chart illustrating an intermittent operation of a temperature-compensated oscillator for explaining a conventional example.

[Explanation of symbols]

Reference Signs List 1 temperature compensation mechanism part, 2 voltage controlled oscillator, 3 crystal oscillator, 4 oscillation circuit, 5 voltage variable capacitance element, 6 temperature sensor, 7 A / D converter, 8 storage circuit, 9 D / A converter, 10 clock source , 11 capacitors, 12 resistors, 13 inverters, 14 comparators, 15 counters, 16 control circuits.

Claims (3)

[Claims] A temperature sensor for generating a detection voltage responsive to temperature, an A / D converter for converting the detection voltage into a digital value, and compensating a frequency temperature characteristic of a crystal oscillator in response to the digital value. A storage circuit having data, a D / A converter for converting the data into a compensation voltage of an analog value, and a clock source for operating the A / D converter, the storage circuit, and the D / A converter in synchronization Wherein the operation of the clock source is stopped immediately after the power is turned on. 2. The digital temperature compensated oscillator according to claim 1, wherein an inverter having an integration circuit on an input side is provided between a power supply terminal of said clock source and a main power supply. 3. A temperature sensor for generating a detection voltage in response to a temperature, a comparator for inputting the detection voltage, which operates in synchronization with a clock source, to one end, and counting an output from the comparator. A counter for inputting a count signal through a D / A converter to the other end of the comparator, a storage circuit connected to the counter and having temperature compensation data, and an output of the comparator for detecting the detection voltage And a control mechanism for stopping the clock source while outputting compensation voltage data based on the count match signal to the storage circuit when the count signal matches, and a compensation voltage of an analog value. A digital temperature-compensated oscillator comprising: a D / A converter that converts the data into a digital signal.