JPS6348447B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a frequency discriminator used to control the automatic oscillation frequency of a frequency modulator, and more particularly to a frequency discriminator with improved start-up and frequency discrimination characteristics upon power-on.

Generally, a self-excited oscillator, which is difficult to obtain high frequency stability by itself, is used as a frequency modulator. Therefore, a method is usually adopted in which the frequency of the modulation self-excited oscillator is automatically and stably controlled using a frequency discriminator. As the above-mentioned frequency discriminator, a frequency discriminator in which the phase comparison function is sufficiently integrated into a circuit and whose center frequency does not change even if the circuit constant changes is disclosed in Patent Application No. 27571 of 1972.

FIG. 1 shows this conventional circuit, which compares the phases of two input signals, and outputs the two input signals from separate output terminals in response to the lead or lag of one phase with respect to the other. a digital phase comparator that outputs a signal with a pulse width proportional to the phase difference; a pair of low-pass waveforms and a high-pass waveform connected separately in series to two output terminals of the phase comparator; It is composed of two wave detectors that receive the outputs of the wave detectors as inputs, two feedthrough capacitors that are separately connected to the outputs of the wave detectors, and an operational amplifier that receives the outputs of the feedthrough capacitors as inputs.

In Figure 1, a reference frequency f _R corresponding to the nominal frequency of the frequency modulator is applied to terminal a, and an input f _V corresponding to the output frequency of a self-excited oscillator for frequency modulation is applied to terminal b. Added. These two inputs are connected to the clipper circuit 101, respectively.
and 102, the signals are shaped into rectangular waves, resulting in outputs 1 and 2, respectively. Outputs 1 and 2 are applied to two inputs of phase comparator 103. In the phase comparator 103, when the phase of output 1 is ahead of the phase of output 2 by 0 to 360 degrees, a pulse is output to terminal d for the period of advance, and the phase of output 1 is ahead of the phase of output 2. When there is a delay of 0 to 360 degrees, a pulse is output to terminal c for the delay period. Outputs 3 and 4 led to terminals c and d pass through a pair of low-pass and high-pass waveforms 104, 106 and 105, 107, respectively, connected in series to detectors 108 and 109, respectively. added to. Detectors 108 and 109 convert their respective input signals into DC voltages. Detector 108,1
Outputs 5 and 6 of 09 are applied to respective inverting or non-inverting input terminals of operational amplifier 110 through feedthrough capacitors C ₁ and C ₂ . The operational amplifier 110 inverts and amplifies the difference between outputs 7 and 8,
Its output 9 is led to terminal e. The output 9 is applied to a terminal for controlling the oscillation frequency of the self-excited oscillator for frequency modulation mentioned above.

Here feedthrough capacitors C ₁ and C ₂ are detector 1
Since the purpose is to cut off the leakage of high frequency components from the 08 and 109 sides, the capacitance values of C ₁ and C ₂ are large, and compared to charging until the DC voltage rises to the output of the detectors 108 and 109 when the power is turned on. It takes a lot of time.

When this frequency discriminator is used in an automatic frequency control circuit, the start-up delay due to charging of the feedthrough capacitors C ₁ and C ₂ greatly reduces the pull-in range to the nominal frequency of the self-excited oscillator for modulation at power-on. Make it narrower.

Furthermore, when the phase difference between the two input signals of the frequency discriminator is 0, the outputs 5 and 6 of the detectors 108 and 109 correspond to the offset voltage of the operational amplifier 110;
In the conventional frequency discriminator, the offset voltage of the operational amplifier 110 tends to fluctuate due to disturbance input. This fluctuation leads to fluctuation in the oscillation frequency of the modulation self-excited oscillator.

The object of the present invention is to provide an automatic frequency control circuit,
To provide a frequency discriminator that has a rapid start-up when power is turned on, stable pull-in of a self-excited oscillator for modulation to the nominal frequency, and less fluctuation in the self-excited oscillation frequency.

To achieve the above object, a frequency discriminator according to the present invention compares the phases of a first input signal having a reference frequency and a second input signal having a frequency of a self-excited oscillator of an automatic frequency control circuit, and determines the phase of one of the signals. a digital phase comparator that outputs a signal with a pulse width proportional to the phase difference between the first and second input signals from separate output terminals in response to a phase lead or lag of the other signal; and a first consisting of a low-pass waver and a high-pass waver connected respectively to the two outputs of the comparator;
a second series circuit, first and second detectors of a voltage doubler rectifier circuit consisting of two diodes inputting the respective outputs of the first and second series circuits; and the first and second detectors. the first, separately connected to the output of
In a frequency discriminator comprising a second feedthrough capacitor and an operational amplifier that amplifies the difference between the outputs of the first and second feedthrough capacitors and whose output is used as an oscillation frequency control signal of the self-excited oscillator, the operational amplifier The first,
By determining the direction of each diode of the second wave detector, and connecting the voltage dividing point of the resistor connected between the power source and the ground to the first and second wave detectors, the first and second wave detectors are connected.
The second detector is provided with a voltage equivalent to the offset voltage of the operational amplifier, and is configured to charge the feedthrough capacitors through the diodes when the power is turned on.

According to the above configuration, the frequency discrimination characteristic becomes stable, and the object of the present invention is completely achieved.

Hereinafter, the present invention will be explained in more detail with reference to the drawings. FIG. 2a is a block diagram showing a first embodiment of a frequency discriminator according to the invention. In the figure, the same parts as in FIG. In other words, the anodes of diodes D ₁ and D ₄ are connected to wave generator 10 via capacitors C ₃ and C ₄ , respectively.
6, 107, the cathodes are connected to the input sides of feedthrough capacitors C ₁ and C _2, respectively, and the cathodes of diodes D ₂ and D ₃ are connected to diodes D 1 and D ₃ , respectively.
It is connected to the anode of D ₄ , and the anodes of diodes D ₂ and D ₃ are connected to each other. Operational amplifier 11
A variable resistor R is connected between the positive power source 0 and the ground, and its voltage dividing point is connected to the anode connection point of the diodes D ₁ and D ₄ .

When the power is turned on, the feedthrough capacitors _C1 and _C2 are rapidly charged in the direction of arrow A because current flows through the diodes _D1 to _D4 to charge the feedthrough capacitors _C1 and _C2 .

The voltage applied to the connection point of the anodes of diodes D ₂ and D ₃ via the variable resistor R is applied to the operational amplifier 11.
Corresponds to an offset voltage of 0. Since this offset voltage is applied, fluctuations in the automatic oscillation frequency of the modulation self-exciting oscillator (not shown) are significantly reduced compared to the conventional one. Specifically, it has decreased to about one-fifth.

FIG. 2b is a block diagram showing a second embodiment of the invention. In this example, the power supply of the operational amplifier 110 is negative, and the directions of the diodes of the detectors 108 and 109 are opposite to those shown in FIG. 2a. Therefore, the feedthrough capacitors C ₁ , C ₂ at power-on
The charging current flows in the direction of arrow B, and feedthrough capacitors C ₁ and C ₂ are rapidly charged.

As explained in detail above, according to the present invention, when the power is turned on, the feedthrough capacitor is rapidly charged, so that the self-excited oscillator for modulation of the automatic frequency control circuit using the circuit of the present invention is stably pulled to the nominal frequency. . Conventionally, a delay circuit or the like is used in the automatic frequency control circuit to ensure that the power starts up when the power is turned on, but these can be omitted. Furthermore, the circuit of the present invention can reduce fluctuations in the automatic oscillation frequency of the self-excited oscillator for modulation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional frequency discriminator, FIG. 2a is a block diagram showing an embodiment of a frequency discriminator according to the present invention, and FIG. 2b is a block diagram showing another embodiment of the present invention. . 101, 102... Clipper circuit, 103...
Digital phase comparator, 104, 105, 10
6,107...Low pass wave generator or high pass wave generator, 108,109...Detector, 110...Operation amplifier, _C1 , _C2 ...Feedthrough capacitor, _C3 to _C6
...Capacitor, _D1 to _D4 ...Diode, R...
...variable resistance.

Claims (1)

[Claims] 1 Compare the phases of the first input signal, which is the reference frequency, and the second input signal, which is the frequency of the self-excited oscillator of the automatic frequency control circuit, and correspond to the lead or lag in the phase of one signal with respect to the phase of the other signal. a digital phase comparator that outputs a signal with a pulse width proportional to the phase difference between the first and second input signals from separate output terminals; A first and a second waveform consisting of a bandpass waveform and a highpass waveform.
a series circuit, and first and second detectors of a voltage doubler rectifier circuit consisting of two diodes inputting the respective outputs of the first and second series circuits;
The first and second detectors are connected separately to the output of the second detector.
In a frequency discriminator comprising a feedthrough capacitor and an operational amplifier that amplifies the difference between the outputs of the first and second feedthrough capacitors and whose output is used as an oscillation frequency control signal of the self-excited oscillator, the power supply of the operational amplifier The first and second electrodes correspond to the polarity of the voltage.
By determining the direction of each diode of the wave detector and connecting the voltage dividing point of the resistor connected between the power source and the ground to the first and second wave detectors, the offset of the operational amplifier can be applied to the first and second wave detectors. A frequency discriminator characterized in that the frequency discriminator is configured to apply a voltage equivalent and charge each of the feedthrough capacitors through each of the diodes when the power is turned on.