JP2551217B2 - Clamp type automatic frequency controller - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a clamp-type automatic frequency control device, and in particular, an FM receiver for effectively utilizing an occupied frequency band when a television signal is transmitted by a satellite repeater by an FM modulation method. The present invention relates to a clamp type automatic frequency control device used for a modulator.

2. Description of the Related Art The conventional clamp type automatic frequency control device of this type is the third one.
The configuration is as shown in the figure. The FM input signal and the reference frequency signal from the reference oscillator 1 are input to the gate circuit 2 and selectively derived by the gate circuit 2.

The FM demodulator 3 FM demodulates the gate output, and the demodulated output is branched into two and supplied to the two S / H (sample hold) circuits 4 and 5, respectively. The S / H circuit 4 samples and holds the demodulated output of the FM input signal, and the S / H circuit 5 samples and holds the demodulated output of the reference frequency signal.

These sample and hold outputs are level-compared by the voltage comparison circuit 6, and this comparison output is output via the loop filter 7. The output of this loop filter is negatively fed back to an FM modulator (not shown), so that automatic frequency control is performed.

Delay circuits 8 and 9 are provided to generate the gate signal of the gate circuit 2 and the sample and hold signals of the S / H circuits 4 and 5.

That is, the delay circuit 8 which receives the clamp pulse trigger signal is triggered by this clamp pulse trigger signal and generates a clamp pulse having a constant pulse width after a fixed time. The gate circuit 2 has the existence period of this clamp pulse.
The FM input signal is selected and the reference frequency signal of the reference oscillator 1 is selected during the other period.

This clamp pulse becomes the sample-hold signal of the S / H circuit 4, and also becomes the sample-hold signal of the S / H circuit 5 after being delayed for a certain period by the delay circuit 9.

In such a conventional clamp-type automatic frequency controller, the timing at which the FM input signal is selected and output by the gate circuit 2 and the timing at which the demodulation voltage of the FM input signal by the demodulation circuit 3 is sampled and held are clamped. It is designed to be performed simultaneously by a pulse signal.

In this case, the instantaneous FM when the output of the gate circuit 2 is switched
The output of the demodulation circuit 3 becomes unstable due to the transient response, and the demodulation voltage cannot be sampled and held accurately. Therefore, there is a drawback that the frequency information sampled and held becomes discontinuous and the frequency stability is poor.

SUMMARY OF THE INVENTION Therefore, the present invention has been made to solve the above-mentioned drawbacks of the prior art, and an object of the present invention is to provide a clamp-type automatic frequency which prevents discontinuity in frequency information sampled and held. It is to provide a control device.

According to the present invention, a reference oscillator that generates a reference frequency signal, a gate circuit that selectively outputs the FM input signal and the reference frequency signal, and an FM demodulation circuit that demodulates the gate output, A circuit that samples and holds the FM demodulated output of the FM input signal during the clamp period, a circuit that samples and holds the FM demodulated output of the reference frequency signal during a predetermined period other than the clamp period, and these two sample and hold outputs A clamp-type automatic frequency control device including a comparison circuit for comparing and performing frequency control according to the output of the comparison circuit, wherein a gate signal is generated earlier than the clamp start point and longer than the clamp period. And an FM input signal is derived from the gate circuit for the duration of the gate signal. A clamp type automatic frequency control device is provided.

Embodiments Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention, and the same portions as those in FIG. 3 are designated by the same reference numerals. In the figure,
The FM input signal f and the reference frequency signal e of the reference oscillator 1 are selectively derived by the gate circuit 2 and become the input g of the FM demodulation circuit 3. This demodulated output h is branched into two, and the S / H circuit 4
And 5 are sample-held respectively.

Both sample and hold outputs i and j are compared by the voltage comparison circuit 6, and the comparison output becomes the frequency control voltage via the loop filter 7, which is the same as in the conventional example of FIG.

The gate signal b in the gate circuit 2 is different from that of the conventional example of FIG. 3, and in this example, the clamp pulse trigger signal a is delayed by the delay circuit 10 for a certain time, and the MMV (single signal is generated at the rising timing of this delay signal. The stable multivibrator) 11 is triggered to obtain the gate signal b.

Incidentally, the sample hold signals c and d of S / H4,5 are the same as those of the conventional example of FIG. 3, and the clamp pulse trigger signal e is delayed by the delay circuit 8 to obtain the sample hold signal c,
This sample hold signal c is further delayed by the delay circuit 9 to obtain the sample hold signal d.

FIG. 2 is a signal a to each section showing the operation of the block of FIG.
2 is a time chart of j, and FIGS. 2 (a) to (j) respectively show signals a to j. The clamp pulse trigger signal a shown in FIG. 2 (a) is delayed by the delay circuit 10 and further passed through the MMV11 to obtain the gate signal b as shown in FIG. 2 (b).

By applying this signal b to the gate circuit 2, the clamp period (the period of FIG. 2 (c)) is started earlier than the starting point.
Moreover, the gate circuit 2 selects the FM input signal f for a longer period than the clamp pulse c. This is shown in FIG. 2 (g).

Next, when the output g of the gate circuit 2 is demodulated by the FM demodulation circuit 3, the waveform shown in FIG. 2 (h) is obtained, and after the output signal of the FM demodulation circuit 3 becomes stable in the S / H circuits 4 and 5. Demodulation voltage V1
And V2 are sample-held respectively.

The voltage comparison circuit 6 compares these two hold voltages,
By inputting the comparison output to the loop filter 7, a stable frequency control voltage can be obtained.

EFFECTS OF THE INVENTION As described above, according to the present invention, after the output of the gate circuit is switched, the FM demodulation output is stabilized and then the sample and hold are performed, so that the accurate demodulation voltage can be sampled and held. There is an effect that the discontinuity of the frequency information is eliminated and the frequency control in the FM modulator becomes stable.

[Brief description of drawings]

1 is a block diagram of an embodiment of the present invention, FIG. 2 is a time chart showing signal waveforms of respective parts of the block of FIG. 1, and FIG.
The figure is a block diagram of a conventional clamp type automatic frequency control device. Explanation of symbols of main parts 1 …… Reference oscillator 2 …… Gate circuit 3 …… FM demodulation circuit 4,5 …… S / H circuit 6 …… Voltage comparison circuit 8,9,10 …… Delay circuit 11 …… MMV

Claims (1)

(57) [Claims] 1. A reference oscillator for generating a reference frequency signal,
A gate circuit that selectively outputs the FM input signal and the reference frequency signal, an FM demodulation circuit that demodulates the gate output, a circuit that samples and holds the FM demodulation output of the FM input signal during a clamp period, and The circuit includes a circuit that samples and holds the FM demodulated output of the reference frequency signal in a predetermined period other than the clamp period, and a comparison circuit that compares the voltages of these two sample and hold outputs. Frequency control is performed according to the output of the comparison circuit. A clamp-type automatic frequency control device having a gate signal generation circuit for generating a gate signal earlier than the clamp start point and longer than the clamp period, and the gate signal generation period from the gate circuit. A clamp type automatic frequency control device characterized in that the FM input signal is derived.