JPH04367102A - Crystal oscillator - Google Patents

Abstract

PURPOSE:To compensate an excess frequency fluctuation due to the change of the surrounding temperature of the crystal oscillator. CONSTITUTION:The surrounding temperature of a voltage controlled crystal oscillator 1 is detected by a temperature detector 3, converted into a digital signal by an A/D converter 4, and sent to an arithmetic circuit 10 with the signal read from a storage element 5. The element 5 holds data generating the voltage controlled crystal oscillator frequency compensation control voltage at the time of normal temperature in advance. The part of the output of the storage element 5 is applied to a differentiation circuit 7 through a D/A converter 6 with the differential waveform corresponding to the change rate of temperature outputted. It is applied to a storage element 9 through the A/D converter 8, and the data compensating the overshoot of the frequency change to be generated according to the change rate of the temperature from the storage element 9. The output is sent to an arithmetic circuit 10, to which the data from the storage elements 5 and 9 are added, applied to the D/A converter 6, and applied to the oscillator 1 after converted into a frequency control analog voltage signal. Then the oscillator 1 is temperature-compensated, and the output frequency is kept constant.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to digital temperature compensation means for crystal oscillators.

0002

2. Description of the Related Art The structure of a conventional digital temperature compensated crystal oscillator is shown in FIG. A temperature detector 3 installed near the voltage-controlled crystal oscillator 1 sends the temperature near the crystal oscillator as a voltage signal to the analog-to-digital converter 4, and the analog-to-digital converter 4 outputs a digital value corresponding to the temperature value. The value is output and a value using that value as an address is read out from the storage element. This value to be read is a value written in advance in the memory element 5 by digitizing a control voltage that compensates for fluctuations in the output frequency of the voltage-controlled crystal oscillator for each temperature. The value from the memory element 5 is input to the digital-to-analog converter 2, the address output signal is input to the voltage controlled crystal oscillator 1 as a frequency control voltage,
The voltage controlled crystal oscillator output is controlled to be constant.

0003

[Problems to be Solved by the Invention] As a general property of crystal oscillators, the transient oscillation frequency when the temperature changes changes in an overshoot manner before stabilizing to the steady state frequency after the temperature change. . The amount of this overshoot tends to increase as the rate of temperature change increases. Therefore, temperature compensation using oscillation frequency compensation data in a steady temperature state, as in the conventional digital temperature compensated crystal oscillator, has the disadvantage that it cannot compensate for transient frequency fluctuations caused by temperature changes, as shown in FIG.

SUMMARY OF THE INVENTION It is an object of the present invention to eliminate such drawbacks and to provide a crystal oscillator capable of compensating for transient frequency fluctuations.

[0005]

[Means for Solving the Problems] The present invention includes a voltage controlled oscillator, a temperature detector that detects the temperature near the voltage controlled oscillator, and a control signal that generates a control signal that constantly controls the oscillation frequency of the voltage controlled oscillator. In a crystal oscillator equipped with a digital control circuit that supplies a voltage controlled oscillator with a lever, the digital control circuit includes a differentiation circuit that calculates a temperature change rate by differentiating a temperature value detected by the temperature detector, and a differential circuit that calculates a temperature change rate by differentiating a temperature value detected by the temperature detector; The present invention is characterized by comprising an arithmetic circuit that generates a control signal by adding the temperature change rate computed by the differential circuit to the temperature value detected by the differential circuit.

[0006]

[Operation] Transient frequency fluctuations are compensated for by using frequency compensation data in a steady state of temperature and frequency compensation data in which the frequency change rate obtained by differentiating this data is added to the frequency compensation data.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of this embodiment. As shown in FIG. 1, this embodiment includes a voltage controlled oscillator 1, a temperature detector 3 that detects the temperature in the vicinity of the voltage controlled oscillator 1, and a control signal that controls the oscillation frequency of the voltage controlled oscillator 1 at a constant level. Generate this voltage controlled oscillator 1
Further, as a feature of the present invention, the digital control circuit includes a differentiation circuit 7 that differentiates the temperature value detected by the temperature detector 3 to calculate the rate of temperature change; A calculation circuit 10 is provided that generates a control signal by adding the temperature change rate calculated by the differentiating circuit 7 to the temperature value detected by the temperature detector 3.

Next, the operation of this embodiment will be explained. The ambient temperature of the voltage-controlled crystal oscillator 1 is detected by a temperature detector 3 placed nearby, converted to a digital signal by an analog-to-digital converter 4, and a digital signal corresponding to the temperature value is read out from a storage element 5. and sent to the arithmetic circuit 10. The memory element 5 holds in advance data for generating a voltage-controlled crystal oscillator frequency compensation control voltage when the temperature is in a steady state. A part of the output of the memory element 5 is applied to the differentiating circuit 7 via the digital-to-analog converter 6, which outputs a differential waveform corresponding to the rate of temperature change, and the output is sent to the memory element 9 via the analog-to-digital converter 8. The storage element 9 outputs data that compensates for the overshoot of the frequency change that occurs depending on the rate of temperature change. The output of the memory element 9 is sent to the arithmetic circuit 10. In the arithmetic circuit 10, the data from the storage element 5 and the data from the storage element 9 are added together, and the data is added to the digital-to-analog converter 6.
is applied to the voltage controlled crystal oscillator 1, which is converted into a frequency controlled analog voltage signal and applied to the voltage control terminal of the voltage controlled oscillator 1, and the voltage controlled crystal oscillator 1 is temperature compensated and the output frequency is kept constant.

Here, in FIG. 2, (a) shows the change in ambient temperature over time, (b) shows the output of the memory element 5 corresponding to this temperature change, and (c) shows the differential circuit 7 corresponding to this output. (d) shows the input voltage to the voltage controlled crystal oscillator 1.

0010

[Effects of the Invention] As explained above, the present invention differentiates a frequency compensation signal in a steady state of a voltage controlled crystal oscillator,
Since the signal is fed back to the voltage controlled crystal oscillator, it is possible to compensate for overshoot in frequency changes due to temperature changes and to maintain the output frequency of the voltage controlled crystal oscillator constant.

[Brief explanation of drawings]

FIG. 1 is a block configuration diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a timing chart showing the operating characteristics of the embodiment of the present invention.

FIG. 3 is a block configuration diagram showing the configuration of a conventional example.

FIG. 4 is a characteristic diagram showing the operating characteristics of a conventional example.

[Explanation of symbols]

1 Voltage controlled crystal oscillator 2 Digital to analog converter 3 Temperature detector 4 Analog-digital converter 5 Memory element 6 Digital to analog converter 7 Differential circuit 8 Analog-digital converter 9 Memory element 10 Arithmetic circuit

Claims (1)

[Claims] 1. A voltage controlled oscillator, a temperature detector that detects the temperature in the vicinity of the voltage controlled oscillator, and a digital signal that generates a control signal that constantly controls the oscillation frequency of the voltage controlled oscillator and supplies it to the voltage controlled oscillator. In the crystal oscillator equipped with a control circuit, the digital control circuit includes a differentiation circuit that calculates a temperature change rate by differentiating the temperature value detected by the temperature detector, and a differential circuit that calculates the rate of temperature change by differentiating the temperature value detected by the temperature detector, and A crystal oscillator comprising: a calculation circuit that generates a control signal by taking into account a temperature change rate calculated by the circuit.