JP2002319821A - Quartz oscillator with frequency correction function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a quartz oscillator with a frequency correction function having a standard long radio wave reception function, that corrects deterioration in the selective characteristic of a quartz filter selecting a standard radio wave due to ambient temperature so as to improve the precision of an oscillated frequency. SOLUTION: The crystal oscillator is provided with the quartz filter 3 selecting a standard radio wave, a temperature compensation voltage generating circuit comprising a temperature sensor 8, an analog/digital converter 9, a ROM 10 and a digital/analog converter 11 or the like, a frequency correction circuit 5 that generates a frequency correction signal from the standard radio wave signal, and a quartz oscillator 6 that outputs an oscillation signal at a prescribed frequency according to the frequency correction signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystal oscillator with a frequency correction function using a long standard radio wave.

[0002]

2. Description of the Related Art Long-wave standard radio waves are time and frequency standards,
And to notify Japan Standard Time (JST) nationwide,
It is sent from a facility located in Otakado and Mt. Fukushima Prefecture and operated by the Ministry of Posts and Telecommunications Research Institute. In recent years, it is well known that various electronic devices using the long-wave standard radio wave have been widely sold.

FIG. 3 is a block diagram showing an embodiment of a conventional crystal oscillator having a frequency correction function using a long-wave standard radio wave. The conventional crystal oscillator with a frequency correction function shown in FIG. 3 includes an antenna 1 for receiving a long-wave standard radio wave,
An amplifier 2 for amplifying a radio wave received by the antenna 1,
A crystal filter 3 for selecting a carrier signal from the signal amplified by the amplifier 2, an amplifier 4 for amplifying the carrier signal selected by the crystal filter, and a comparison between the carrier signal amplified by the amplifier 4 and an oscillator output signal described later. A frequency correction circuit for generating a frequency correction signal; and a crystal oscillator for outputting an oscillation signal having the same frequency accuracy as the carrier signal in accordance with the frequency correction signal. The oscillator output signal of the crystal oscillator 6 is fed back to the frequency correction circuit 5 and is referred to for generating the frequency correction signal.

The conventional crystal oscillator with a frequency correction function shown in FIG. 3 operates as follows. First, the antenna 1 receives a long-wave standard radio wave and supplies it to the amplifier 2 as a reception signal. The amplifier 2 amplifies this and supplies it to the crystal filter 3. The crystal filter 3 selects a carrier signal (40 kHz) from the amplified received signal and supplies it to the amplifier 4. The amplifier 4 amplifies the carrier signal and supplies it to the frequency correction circuit 5 as a reference signal. The frequency correction circuit 5 compares the reference signal with an oscillator output signal described later, generates a frequency correction signal, and supplies the frequency correction signal to the crystal oscillator 6. The crystal oscillator 6 oscillates at a predetermined frequency according to the frequency correction signal, and feeds back the oscillation output signal to the frequency correction circuit 5. As described above, since the oscillation frequency of the crystal oscillator 6 is feedback-controlled by the frequency correction circuit 5, the oscillation output frequency can be obtained with the same frequency accuracy as the carrier signal selected from the long-wave standard radio wave.

[0005]

However, the conventional oscillator having the frequency correction function described above has the following problems. In other words, in order to select a carrier signal (40 kHz) having a constant frequency and a good C / N from the received long-wave standard radio wave, a narrow-band quartz filter 3 having excellent selection characteristics must be used. On the other hand, the long-wave standard radio wave has a pulse modulation waveform with a modulation speed of 1 bit / sec. In order to extract an excellent reference signal from the modulation waveform, the crystal filter 3 having a band of at least several Hz is required.

However, it has been found that the crystal filter 3 having a band of about several Hz is easily affected by a change in ambient temperature, and the center frequency of the crystal filter 3 is shifted by about several Hz due to a change in ambient temperature. For example, taking as an example a low-frequency crystal resonator (VTC-200 series) manufactured by the applicant, the deviation of the center frequency is Δf = fK
(T-25) It is understood that it is given by ² . Here, f is the standard frequency of the crystal unit, K is the secondary temperature coefficient,
T represents the ambient temperature. Therefore, now f = 40 kHz, K =
Assuming −3.5 × 10 ⁻⁸ / ° C. ² and T = −10 to 60 ° C., the frequency shift Δf with respect to the ambient temperature of 25 ° C. is as follows.

Therefore, if a wide band is used as the crystal filter, the above frequency deviation hardly causes a problem. However, since the wide band is used, the selection characteristic is sacrificed, so that the accuracy of the frequency correction is deteriorated. On the other hand, if a narrow band signal is used, C
In the worst case, a situation arises where a reference signal cannot be selected in addition to the deterioration of / N. In order to avoid this, there has been proposed a method in which the entire crystal filter is placed in a thermostat to suppress the frequency deviation of the crystal filter.However, a space for the thermostat is required, and a temperature control circuit must be added. It is complicated and not practical.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a crystal oscillator having a frequency correction function which is not affected by a change in ambient temperature and has excellent frequency accuracy. And

[0009]

In order to solve the above-mentioned object, a crystal oscillator with a frequency correction function according to the present invention according to the present invention has a long-wave standard radio wave receiving function and is selected from the long-wave standard radio wave. In a crystal oscillator having a frequency correction function of referring to a carrier signal as a reference signal for frequency correction, a long-wave standard radio receiver, a crystal filter for selecting a carrier signal from a signal amplified by the long-wave standard radio receiver, A temperature compensation circuit for temperature-compensating the characteristics of the crystal filter, a frequency correction circuit for generating a frequency correction signal from the carrier signal selected by the crystal filter, an oscillation signal having a predetermined frequency in accordance with the frequency correction signal, and an oscillation output A crystal oscillator for supplying a signal to the frequency correction circuit.

According to a second aspect of the present invention, there is provided a crystal oscillator having a frequency correcting function according to the first aspect, wherein the temperature compensating circuit senses an ambient temperature to generate a sensing voltage, and the temperature sensor. An A / D converter for converting a sensed voltage from the A / D into a digital signal, a ROM (storage means) for inputting the digital signal from the A / D converter as an address signal and outputting a temperature compensation voltage (digital signal), A D / A converter that converts a temperature compensation voltage (digital signal) output from the ROM into an analog signal and outputs the analog signal;
Temperature compensation voltage (analog signal) from the D / A converter
And a variable capacitance diode whose impedance changes according to the following. The variable capacitance diode is connected in series to an input or an output of the crystal filter.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on illustrated embodiments. FIG. 1 is a block diagram showing an embodiment of a crystal oscillator with a frequency correction function according to the present invention. The crystal oscillator with the frequency correction circuit function shown in FIG. 1 includes an antenna 1 for receiving a long-wave standard radio wave,
An amplifier 2 for amplifying a radio wave received by the antenna 1,
A crystal filter 3 for selecting a carrier signal from the signal amplified by the amplifier 2, a variable capacitance diode 7 for compensating for a temperature change in the selection characteristics of the crystal filter 3, and a carrier signal supplied via the variable capacitance diode 7 An amplifier 4 for amplifying the signal, a frequency correction circuit 5 for comparing a carrier signal amplified by the amplifier 4 with an oscillator output signal described later to generate a frequency correction signal, and a frequency accuracy equivalent to the carrier signal according to the frequency correction signal. A temperature sensor 8 that senses ambient temperature and outputs a sensed voltage, an A / D converter 9 that converts the sensed temperature to a digital signal, and stores the temperature compensation voltage as digital data. When the digital signal from the A / D converter 9 is input as an address signal, the temperature compensation voltage is converted to a digital signal. And a D / A converter 11 for converting a temperature compensation voltage (digital signal) supplied from the ROM 10 into an analog signal, and a temperature output from the D / A converter 11. The compensation voltage is supplied to the cathode of the variable capacitance diode 7 via the resistor R1, and the anode is grounded via the resistor R2. The oscillator output signal of the crystal oscillator 6 is fed back to the frequency correction circuit 5 and is referred to for generating the frequency correction signal.

The operation of the crystal oscillator with a frequency correction function shown in FIG. 1 will be described below. First, the antenna 1 receives a long-wave standard radio wave and supplies it to the amplifier 2 as a reception signal. The amplifier 2 amplifies this and supplies it to the crystal filter 3. The crystal filter 3 selects a carrier signal (40 kHz) from the amplified received signal and supplies it to the cathode of the variable capacitance diode 7.

The D / A converter 1 is connected to the cathode of the variable capacitance diode 7 via a resistor R1 having a high resistance value.
1 supplies a temperature compensation voltage to be described later. Therefore, the impedance of the variable capacitance diode 7 changes according to the temperature compensation voltage, and the characteristic change due to the ambient temperature of the crystal filter connected in series with the diode 7 is compensated. Therefore, the carrier signal that has passed through the crystal filter whose temperature has been compensated by the variable capacitance diode 7 is amplified by the amplifier 4 and supplied to the frequency correction circuit. Hereinafter, although the details are omitted because it is the same as the conventional example described with reference to FIG. 3, a signal having the same frequency accuracy as the carrier signal is obtained as the oscillation output signal of the crystal oscillator 6.

Next, a process of generating the temperature compensation voltage will be described. First, the ambient temperature is sensed, and the temperature sensor 8 outputs a sensed voltage. The A / D converter 9 converts the sensing voltage into a digital signal and supplies it to a ROM (storage means). Here, the ROM (storage means) stores and stores the temperature compensation voltage as digital data. The ROM (storage means) refers to the digital signal input from the A / D converter 9 as an address signal and outputs a stored digital signal (temperature compensation voltage) corresponding thereto. The D / A converter 11 converts the digital signal (temperature compensation voltage) into an analog signal and supplies the analog signal to the cathode of the variable capacitance diode 7 via the resistor R1. Therefore, an appropriate temperature compensation voltage is supplied from the D / A converter 11 to the anode of the variable capacitance diode 7 in accordance with the ambient temperature, and the impedance of the variable capacitance diode 7 changes with the temperature compensation voltage, thereby changing the characteristic of the crystal filter 3. Temperature changes can be compensated.

Note that a plurality of variable capacitance diodes connected in parallel may be used according to the temperature characteristics of the crystal filter 3. Alternatively, as shown in FIG. 2, two or a plurality of variable capacitance diodes Back To Bac
The cathodes may be connected in a k-type, and a temperature compensation voltage may be supplied to the cathodes via a resistor R1. Alternatively, it is also possible to use a combination of the series connection and the parallel connection of the variable capacitance diodes, and in any case, the combination may be selected so as to obtain optimum temperature compensation according to the temperature characteristics of the crystal filter. In the embodiment of the present invention, the variable capacitance diode is inserted on the output side of the crystal filter. However, it goes without saying that the same effect can be obtained by inserting the variable capacitance diode on the input side.

Further, as for the method of generating the temperature compensation voltage, a method of generating the temperature compensation voltage in an analog manner by combining a temperature sensor and an operational amplifier is also possible. R
Since the contents can be easily handled by rewriting the contents of the OM according to the characteristics of the crystal filter, a method of digitally processing the sensing voltage of the temperature sensor has many advantages.

[0017]

As described above, according to the present invention, in a conventional crystal oscillator with a frequency correction function having a function of receiving a long-wave standard radio wave, a narrow-band crystal filter for selecting a carrier signal has a selection characteristic due to the influence of an ambient temperature. To solve the problem that high-precision frequency correction cannot be performed due to the inability to select a carrier signal with excellent signal purity.A temperature compensation circuit is added to the crystal filter, Since a high-purity carrier signal can be selected by the filter, the present invention is very effective in providing a crystal oscillator with a frequency correction function that is highly resistant to temperature changes and enables high-precision frequency correction.

[0018]

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a crystal oscillator with a frequency correction function according to the present invention.

FIG. 2 is a block diagram showing a combination example of variable capacitance diodes of the crystal oscillator with a frequency correction function according to the present invention.

FIG. 3 is a block diagram showing an embodiment of a conventional crystal oscillator with a frequency correction function.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Antenna 2, 4 ... Amplifier 3 ... Crystal filter 5 ... Frequency correction circuit 6 ... Crystal oscillator 7 ... Variable capacitance diode 8 ... Temperature sensor 9 ... A / D converter 10 ... ROM 11 ... D / A converter R1,2,3 ... Resistor

Claims (2)

[Claims] 1. A crystal oscillator having a long-wave standard radio wave reception function and a frequency correction function for referring to a carrier signal selected from the long-wave standard radio wave as a reference signal for frequency correction, comprising: a long-wave standard radio receiver; A crystal filter for selecting a carrier signal from a signal amplified by the long-wave standard radio receiver, a temperature compensation circuit for temperature-compensating the characteristics of the crystal filter, and a frequency correction for generating a frequency correction signal from the carrier signal selected by the crystal filter A crystal oscillator having a frequency correction function, comprising: a circuit; and a crystal oscillator that outputs an oscillation signal of a predetermined frequency in accordance with the frequency correction signal and feeds back the oscillation output signal to the frequency correction circuit. 2. The temperature compensation circuit according to claim 1, wherein the temperature sensor senses an ambient temperature and generates a sense voltage, an A / D converter that converts a sense voltage from the temperature sensor into a digital signal, and the A / D converter. (Storage means) for inputting a digital signal from a device as an address signal and outputting a temperature compensation voltage (digital signal), and a D / A for converting the temperature compensation voltage (digital signal) output from the ROM into an analog signal and outputting the analog signal A converter and a variable capacitance diode whose impedance changes according to a temperature compensation voltage (analog signal) from the D / A converter, wherein the variable capacitance diode is connected in series to an input or an output of the crystal filter. The crystal oscillator with a frequency correction function according to claim 1, wherein: