JPH06252642A - Control circuit for frequency characteristic of digitally controlled temperature compensation type crystal oscillator - Google Patents

Abstract

PURPOSE:To obtain a control circuit with a frequency characteristic by which new provision of a variable capacitance diode is unnecessitated when a REFRESH function is added to the digitally controlled temperature compensation type crystal oscillation having no REFRESH function and it is unnecessitated to change a constant of an element decided already and provided in a peripheral part of the variable capacitance diode. CONSTITUTION:Correction data correcting the characteristic of an oscillating frequency of a crystal vibrator 51 with respect to a temperature change are stored in a memory 30 and the correction data are read from a memory 30 in response to the ambient temperature of the crystal vibrator 51. On the other hand, a voltage resulting from a difference between a frequency of a signal received from a base station and an oscillated frequency of a crystal oscillator is converted into a digital signal and the correction data read from the memory 30 are added by an adder 80 and the sum is applied to a variable capacitor diode VC1 to control the oscillated frequency of a crystal oscillator 50.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digitally controlled temperature-compensated crystal capable of correcting the characteristics of the oscillation frequency with respect to the ambient temperature of a crystal oscillator by digital control and varying the oscillation frequency in accordance with an external frequency control voltage. The present invention relates to a control circuit for frequency characteristics of an oscillator.

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram showing an example of a conventional digital control temperature compensation type crystal oscillator (digital TCXO).

In this conventional example, a crystal oscillator 51 and an oscillator 5 are used.
0 and the frequency characteristic control circuit 3, and the frequency characteristic control circuit 3 applies an analog voltage (correction voltage) corresponding to the ambient temperature of the crystal unit 51 to the varicap diode V.
The capacitance of the varicap diode VC1 is changed by applying it to C1, and the oscillation frequency is controlled according to this capacitance change.

That is, the frequency characteristic control circuit 3 stores in advance in the memory 30 the correction data for correcting the characteristic of the oscillation frequency of the crystal unit with respect to the temperature change, and the crystal unit 51.
The ambient temperature of the sensor 3 is detected by the temperature detector 10, the detected temperature data is converted into a digital signal by the A / D converter 20, and the digital data is used as address information in the memory 3
The correction data is read from 0, the read correction data is converted into an analog voltage by the D / A converter 40, and the analog voltage is converted into a varicap diode VC.
Varycap diode V
The capacitance of C1 is changed, and the oscillation frequency is controlled in accordance with this change in capacitance. Also, the frequency stability of this digitally controlled temperature-compensated crystal oscillator is very high compared to other oscillators, and it is within the operating temperature range (for example, -20 ° C).
At + 70 ° C), the frequency change is ± 0.1, for example.
It is 0.3 ppm.

FIG. 4 is a diagram showing a frequency characteristic control circuit 4 in the case where the conventional example shown in FIG. 3 is circuit-configured by using a microcomputer (microcomputer) MC1.

In the control circuit 4 of this frequency characteristic, A
The / D conversion unit and the memory access function are built in the microcomputer MC1, and the digital value output from the A / D conversion unit serves as memory access address information, and the microcomputer MC1 reads correction data from the memory 30 based on this address information. .

[0007]

By the way, there is a case where the crystal oscillator 51 or the like undergoes a secular change, and the change in the oscillation frequency due to this secular change may be larger than the change in the oscillation frequency due to the temperature change. It is necessary to correct the oscillation frequency as well as the oscillation frequency due to secular change.

To correct the oscillation frequency due to secular change, REFRESH (REcieved signal FREquency Stab
ilized syntHesizer) function is known. This REF
In the RESH function, the base station always transmits a radio wave of the same frequency, the crystal oscillator side receives the radio wave transmitted by the base station, and the oscillation frequency is sequentially corrected inside the oscillator according to the frequency of the received radio wave. It is a thing. That is, the oscillation frequency can be changed with respect to the frequency of the radio wave transmitted from the base station. The crystal oscillator whose oscillation frequency changes according to the external control voltage is called a VCXO.

FIG. 5 is a diagram showing a control circuit 5 for frequency characteristics of a crystal oscillator which is considered as a VCXO.

In other words, the control circuit 5 is the same as the conventional control circuit 3 shown in FIG.
The varicap diode VC2 and the DC blocking capacitor C2 are added.

The difference detector 70 compares the frequency of the radio wave transmitted by the base station with the frequency of the signal output by the oscillator 50, and outputs a voltage corresponding to the frequency of the difference. The cap diode VC2 is a circuit that generates a capacitance corresponding to the voltage corresponding to the frequency of the difference output by the difference detection unit 70.

However, in the control circuit 5 shown in FIG. 5, there is a problem that two varicap diodes must be used. Further, in the control circuit 5 shown in FIG. 5, the conventional control circuits 3 and 4 shown in FIGS.
When modifying the control circuit 5 by adding the EFRESH function later, it is necessary to reconsider the constants (capacitances of the capacitors C1 and C2) of the elements around the varicap diode VC1 that have been once determined. There is a problem that the constant reexamination work is complicated.

According to the present invention, when the REFRESH function is added to the digitally controlled temperature-compensated crystal oscillator having no REFRESH function, it is not necessary to additionally provide a varicap diode, and the varicap diode is provided around the varicap diode. It is an object of the present invention to provide a control circuit of the frequency characteristic of a digitally controlled temperature compensated crystal oscillator, which does not require changing the already determined constant of the device.

[0014]

According to the present invention, correction data for correcting the characteristic of the oscillation frequency of a crystal unit with respect to a temperature change is stored in a memory, and the correction data is read from the memory according to the ambient temperature of the crystal unit. On the other hand, the value obtained by converting the voltage difference between the frequency of the signal received from the base station and the oscillation frequency of the crystal oscillator into digital value, and the correction data read from the memory are added, and this added value is varicapped. It is applied to a diode and the oscillation frequency of the crystal oscillator is controlled according to the capacitance change of the varicap diode.

[0015]

The present invention stores the correction data for correcting the characteristic of the oscillation frequency of the crystal unit against the temperature change in the memory,
The correction data is read from the memory according to the ambient temperature of the crystal unit, while the value of the difference between the frequency of the signal received from the base station and the oscillation frequency of the crystal oscillator is converted to digital and read from the memory. And the correction data
This added value is applied to the varicap diode, and the oscillation frequency of the crystal oscillator is controlled according to the capacitance change of the varicap diode. Therefore, it is sufficient to provide one varicap diode, and the REFRESH function is also provided. When added, there is no need to change the already determined constants of the elements around the varicap diode.

[0016]

1 is a circuit diagram showing a control circuit 1 for frequency characteristics of a digitally controlled temperature-compensated crystal oscillator according to an embodiment of the present invention.

In this embodiment, the temperature detecting section 10 is
It is configured by a series circuit of a thermistor TH and a resistor R1 installed in the vicinity of the crystal unit 51, one end of the resistor R1 is connected to the power supply V _cc , the other end of the resistor R1 is connected to the thermistor TH, and the resistor R1 is connected. A connection point with the thermistor TH serves as an output terminal of the temperature detection unit 10. The temperature detector 10 is an example of a temperature detector that detects the ambient temperature of the crystal unit.

The first A / D converter 21 includes a temperature detector 1
The detected temperature data (analog data) output by 0 is converted into digital data, and this digital data is supplied to the memory 30 as address information.

The memory 30 stores correction data for correcting the characteristics of the oscillation frequency of the crystal unit 51 with respect to temperature changes, and the output data of the first A / D converter 21 is used as an address, Correction data for correcting the frequency change of the crystal unit 51 with respect to the change is stored corresponding to the above address.

The receiver 60 receives a radio signal from the base station, and the difference detector 70 receives the frequency of the signal received from the base station (the signal received from the outside of the digitally controlled temperature-compensated crystal oscillator). And the output frequency of the oscillator 50 are detected, and a voltage corresponding to this difference is output, and the second A / D conversion unit 71 converts the voltage output by the difference detection unit 70 into digital data. To do.

The addition section 80 is an example of addition means for adding the digital data output from the second A / D conversion section 71 and the correction data read from the memory 30, and is a D / A.
The converter 41 converts the output data of the adder 80 into an analog voltage.

The analog voltage output from the D / A converter 41 is applied to the cathode terminal of the varicap diode VC1, and the anode terminal of the varicap diode VC1 is grounded. Varicap diode VC
The cathode terminal of No. 1 is connected to the oscillator 50. In this embodiment, the varicap diode VC1
The oscillation frequency of the oscillator 50 is controlled according to the capacitance change of

Next, the operation of the above embodiment will be described.

First, the ambient temperature of the crystal unit 51 is detected by the temperature detecting section 10, the detected temperature data is converted into a digital signal by the first A / D converting section 21, and this digital data is converted into address information. Used as a memory 30
The correction data is read from, and the read correction data is applied to one input terminal of the adder 80. On the other hand, when the receiving section 60 receives the radio wave transmitted from the base station, the frequency of the received signal and the frequency of the signal output by the oscillator 50 are compared by the difference detecting section 70, and the voltage corresponding to this difference frequency is received. Is output by the difference detection unit 70, the output voltage of the difference detection unit 70 is converted into digital data by the second A / D conversion unit 71, and applied to the other input terminal of the addition unit 80.

Then, the output voltage of the adder 80 is converted into an analog voltage by the D / A converter 41, the capacitance of the varicap diode VC1 changes according to this analog voltage, and the oscillator 50 of the oscillator 50 changes according to this capacitance. Oscillation frequency changes.

In the above embodiment, the oscillator 50 and the difference detector 7 are used.
0, the adder 80, the D / A converter 41, and the varicap diode VC1 form a feedback loop, and the output frequency of the oscillator 50 is always the same as the frequency of the signal oscillated by the base station. Even if the crystal oscillator 51 and the like change over time, the fluctuation of the oscillation frequency due to the change over time is corrected.

After the power is turned on, the temperature detector 1
0, the first A / D converter 21, and the memory 30 do not exist, the oscillator 50 can be operated by the receiver 60 and the loop.
The output frequency of is always the same as the frequency of the signal transmitted by the base station, but if it does not oscillate at the specified frequency (the frequency is almost the same as the frequency of the signal transmitted by the base station) when the power is turned on, The temperature detection unit 10, the first A / D conversion unit 21, and the memory 30 are indispensable because they cannot be pulled to the same frequency as the frequency of the signal transmitted by the station.

In the above-described embodiment, the digitally controlled temperature compensated crystal oscillator having no REFRESH function is used as the RE.
When the FRESH function is added, it is not necessary to add a varicap diode, and it is not necessary to reexamine the constant of the elements around the varicap diode VC1 (capacitance of the capacitor C1) that has already been determined. That is, R
The capacitance of the capacitor C1 is the same before and after the addition of the EFRESH function.
It is easy to design the SH function later.

FIG. 2 is a diagram showing a frequency characteristic control circuit 2 in the case where the microcomputer MC1 is used to form the circuit of the above embodiment.

In the control circuit 2 of this frequency characteristic, the first A / D converter 21 and the second A / D converter 21 in the control circuit 1 are used.
The D conversion unit 71, the memory access function, and the addition unit 80 are built in the microcomputer MC2, and the digital value output by the first A / D conversion unit 21 becomes memory access address information. Based on this address information, the microcomputer MC2 Reads the correction data from the memory 30, and the value of the read correction data and the digital value output by the second A / D converter 71 are added by the microcomputer MC2, and the addition result is D / A converted. It is supplied to the section 41.

Instead of using the thermistor TH, the temperature detecting section 10 may be constructed using a temperature detecting element having a positive temperature coefficient of resistance.

[0032]

According to the present invention, a digitally controlled temperature-compensated crystal oscillator having no REFRESH function is provided.
When the ESH function is added, there is an effect that it is not necessary to add a varicap diode and it is not necessary to change the already determined constant of the elements provided around the varicap diode.

[Brief description of drawings]

FIG. 1 is a diagram showing a frequency control circuit 1 of a digitally controlled temperature-compensated crystal oscillator according to an embodiment of the present invention.

FIG. 2 is a diagram showing a frequency characteristic control circuit 2 in the case where the above embodiment is circuit-configured using a microcomputer MC1.

FIG. 3 is a circuit diagram showing an example of a conventional digitally controlled temperature-compensated crystal oscillator.

4 is a diagram showing a frequency characteristic control circuit 4 in the case where the conventional example shown in FIG. 3 is circuit-configured using a microcomputer MC1.

FIG. 5 is a diagram showing a control circuit 5 for frequency characteristics of a crystal oscillator that is considered as a VCXO.

[Explanation of symbols]

1 to 5 ... Control circuit for frequency characteristics of digitally controlled temperature-compensated crystal oscillator, 10 ... Temperature detector, 21 ... First A / D converter, 30 ... Memory, 41 ... D / A converter, 50 ... Oscillator , 51 ... Crystal oscillator, 60 ... Receiving unit, 70 ... Difference detecting unit, 71 ... Second A / D converting unit, VC1, VCV2 ... Varicap diode.

Claims (1)

[Claims] 1. A temperature detecting means for detecting an ambient temperature of a crystal unit; a first A / D converting means for converting detected temperature data detected by the temperature detecting means into digital data;
A memory in which the output data of the first A / D conversion means is used as an address, and the correction data for correcting the frequency change of the crystal unit with respect to the temperature change is stored corresponding to the address; the digital control temperature. Second A / D conversion means for converting a voltage corresponding to the difference between the frequency of the signal received from the outside of the compensation type crystal oscillator and the output frequency of the digital control temperature compensation type crystal oscillator into digital data;
Adder for adding the digital data output by the second A / D converter and the correction data read from the memory; D / A converter for converting the output data of the adder into an analog voltage Means; and a varicap to which the analog voltage converted by this D / A conversion means is applied
A control circuit for frequency characteristics of a digitally controlled temperature-compensated crystal oscillator, comprising: a diode; and controlling an oscillation frequency according to a change in capacitance of the varicap diode.