JPS6269754A - Carrier recovery circuit - Google Patents

Abstract

PURPOSE:To stably recover a carrier necessary for demodulating a PSK modulation signal by permitting a sample holding circuit to hold the control voltage of a voltage controlled oscillator VCO stable. CONSTITUTION:While a synchronization detecting circuit 11 detects the synchro nization between the PSK modulation signal and the output signal of the VCO 10, a switch 14a at the input side of the sample holding circuit 14 is in an ON state, and a charge is charged and discharged to a capacitor 14b. While the input signal of the synchronization detecting circuit 11 is an FM modulation signal, the input side switch 14a is an OFF state, and the output of the sample holding circuit 14 becomes a constant voltage due to the charge of the capacitor 14b. the oscillation frequency of the output signal of the VCO 10 is controlled by the output voltage of the sample holding circuit 14. However, since the output voltage of the sample holding circuit 14 has less fluctuation, the output signal of the VCO 10 is stable. Accordingly, while the output signal of a band amplifier 8 is the PSK signal, the synchronization detecting circuit 11 can stably detect the synchronization at the beginning of said period.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a carrier regeneration circuit, and in particular, it is proposed as a new transmission method for television signals, in which video signals are FM modulated and audio signals are time-divisionally PSK modulated. This invention relates to an improvement of a carrier regeneration circuit for better demodulation of audio signals in a system in which a voice signal is demodulated.

[Conventional technology]

The new modulation method proposed here is based on the material "
New transmission method for high-definition television % Type % This is a transmission method as shown in Figure 2.

That is, in this MUSE method, the video signal and control signal are FM modulated, the clamp level is not modulated, and the audio information is P
SK modulation is used, and the clamp level and audio information are transmitted so as to be included within the vertical blanking period.

Although transmission using this method is not currently in practical use, there are receivers for this broadcasting method using satellites (12 GHz:
As for the SHF band, a configuration as shown in FIG. 3 can be considered.

In the figure, 1 is an input terminal of the receiver, 2 is a tuning section for the input signal input to the input terminal 1 of the receiver, 3 is a band amplifier that receives the output signal of the tuning section 2, and 4 is a band amplifier for the input signal input to the input terminal 1 of the receiver. 5 is an A/D converter that converts the output signal of the FM demodulator 4 into A/D; 6 is a digital processing circuit that processes the output signal of the A/D converter 5; 7 is an FM demodulator that demodulates the output signal; This is a digital image signal output terminal.

8 is a band amplifier that receives the output signal of the tuning section 2;
9 represents the output signal of the bandpass amplifier 8 and the voltage controlled oscillator (hereinafter V
10 is a control circuit that receives the output signal of the control circuit 9 and the output signal of the synchronous detection circuit; 10 is a synchronous detection circuit that receives the output signal of the control circuit 9; VCOll is a synchronous detection circuit that receives the output signal of the band amplifier 8; 12 is a control circuit 9. A carrier regeneration circuit composed of VCOIO, 13 is a synchronous detection circuit 1
This is a PSK demodulation output terminal connected to the output terminal of No. 1.

Next, the operation will be explained. The input signal arriving at the input terminal 1 is frequency-converted by the tuning section 2, and the band amplifier 3 amplifies only the necessary band of the output signal of the tuning section 2, and converts the frequency of the input signal arriving at the input terminal 1 into an F M
Send to ijjill device 4. The FM demodulator 4 detects and demodulates video signals, control signals, etc.
The detected output is converted into digital data by an A/D converter 5, and the converted data is subjected to arithmetic processing in a digital processing circuit 6, and an output signal is obtained at a digital image signal output terminal 7.

On the other hand, the band amplifier 8 amplifies the necessary band of the output signal of the tuning section 2, and the output signal of the band amplifier 8 is transmitted to the control circuit 9.
．． The control circuit 9 inputs the output signal of the band amplifier 8, the output signal of the VCO iO, and the demodulated output of the synchronous detection circuit 11, and performs control related to well-known carrier regeneration such as an inverse modulation type. The oscillation frequency of the VCOIO is controlled by the output signal of the control circuit 9. Further, the synchronous detection circuit 11 performs synchronous detection of the output signal of the VCOIO and the output signal of the band amplifier 8, and demodulates the PSK modulation portion of the output signal of the band amplifier 8. And P.S.
PSK demodulated audio data is obtained at the KIXgN output terminal 13.

[Problem that the invention seeks to solve]

A conventional satellite high-definition television broadcasting receiver is configured as described above, and the output of the band amplifier before the carrier regeneration circuit is a composite signal of FM and PSK.
In the first half of the SK signal period, the VCO control voltage of the carrier regeneration circuit becomes unstable due to the influence of the immediately preceding FM signal period, so the VCO oscillation frequency is unstable and PSK demodulation is not performed correctly. There was a point.

The present invention was made to solve the above-mentioned problems, and provides a carrier regeneration circuit that can stabilize the control voltage of the VCO during the period when the output of the band amplifier is a PSK signal and have little fluctuation. The purpose is to obtain.

[Means for solving problems]

In the carrier regeneration circuit according to the present invention, during the period in which the output of the band amplifier at the front stage of the carrier regeneration circuit is an FM modulation signal, the VCO
A sample and hold circuit is added for maintaining the control voltage in a stable state during the immediately preceding PSK modulation signal period.

[Effect]

In this invention, since the sample and hold circuit maintains the control voltage of vCO in a stable state, the carrier necessary for demodulating the PSK modulated signal is regenerated stably.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure shows a carrier regeneration circuit according to an embodiment of the present invention,
In the figure, 1 is the input terminal of the receiver, 2 is a tuning section for the input signal input to the receiver 1, 3 is a band amplifier that receives the output signal of the tuning section 2, and 4 is the input terminal for the output signal of the band amplifier 3. An FM demodulator 5 demodulates the output signal of the FM demodulator 4 to A
6 is a digital processing circuit that processes the output signal of the A/D converter 5, and 7 is a digital image signal output terminal.

8 is a band amplifier that receives the output signal of the tuning section 2;
9 is a control circuit to which the output signal of the band amplifier 8, the output signal of the VCO, and the output signal of the synchronous detection circuit are input; 14 is the control circuit that receives the output signal of the control circuit 9 and is controlled by the output signal of the digital processing circuit 6; Sample and hold circuit, 10
v which inputs the output signal of the sample and hold circuit 14
COll is a synchronous detection circuit that uses the output signal of the band amplifier 8 and the output signal of the VCOIO manually, and COll is a control circuit 9.
．． A carrier regeneration circuit includes a VCOIO and a sample and hold circuit 14, and 13 is a PSKfiilli output terminal connected to the output signal of the synchronous wave circuit 11.

Next, the operation will be explained. The input signal arriving at the input terminal l is frequency-converted by the tuning section 2, and the band amplifier 3 amplifies only the necessary band of the output signal of the tuning section 2, and converts it into an FM signal.
It is sent to demodulator 4. The FM demodulator 4 detects and demodulates video signals, control signals, etc., the detection output of the FM demodulator 4 is converted into digital data by the A/D converter 5, and the converted data is sent to the digital processing circuit 6. The arithmetic processing is performed, and an output signal is obtained at the digital image signal output terminal 7.

On the other hand, the band amplifier 8 amplifies the necessary band of the output signal of the tuning section 2, and the control circuit 9. The output signal is sent to the synchronous detection circuit 11. The synchronous detection circuit 11 constantly performs synchronous detection of the output signal of the third day of band amplification and the output signal of the VCOIO, and the control circuit 9 performs inverse modulation using the output signals of the band amplifier B, VCOIO, and the synchronous detection circuit 11 as inputs. Controls related to well-known carrier regeneration such as type etc. are performed, and the output signal is inputted to the sample and hold circuit 14.

Here, Fig. 4(a) shows the format of the output signal of the band amplifier 8, Fig. 4(c) shows the control pulse sent from the digital processing circuit 6 to the sample and hold circuit 14, and Fig. The configuration is shown below.

In addition to the digital signal processing function, the digital processing circuit 6 has various clock generation functions.
In this example, PSK as shown in the same figure (C) is used.
A clock that is ON during the FM period and OFF during the FM period is used as a control pulse for the sample and hold circuit 4.

The switch 14a on the input side of the sample and hold circuit 14 shown in FIG. That is, during a period in which the synchronous detection circuit 11 performs synchronous detection of the PSK modulation signal and the output signal of the VCOIO, the switch 14a on the input side of the sample and hold circuit 14 is in the ON state, and the capacitor 14b is charged and discharged. Then, the input signal of the synchronous detection circuit 11 is F
While the signal is an M modulated signal, the switch 14a on the input side of the figure (C) is in an OFF state, and the output of the sample and hold circuit 14 becomes a constant voltage due to the charge of the capacitor 14b. V
The oscillation frequency of the COIQ output signal is controlled by the output voltage of the sample and hold circuit 14, but since the output voltage of the sample and hold circuit 14 has little fluctuation as described above, the VCOIO output signal is stable. Therefore, the synchronous detection of the synchronous detection circuit 11 is performed stably from the beginning of the period in which the output signal of the band amplifier 8 is a PSK signal. In this way, the PSK demodulation output terminal 13 receives audio data that has been correctly PSK demodulated from the beginning of the audio signal period.

〔Effect of the invention〕

As described above, according to the carrier regeneration circuit according to the present invention, the composite signal converts the 'MIFB voltage applied to the VCO into FM
Since the stable value of the PSK modulation signal period immediately before changing to the modulation signal is sampled and held, there is an effect that accurate PSK demodulation can be obtained with a simple circuit configuration.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a receiver using a carrier regeneration circuit according to an embodiment of the present invention, Fig. 2 is a diagram showing a MUSE transmission format, and Fig. 3 is a receiver using a conventional carrier regeneration circuit. FIG. 4 is a block diagram showing the configuration of the sample six-handed circuit shown in FIG. 1 and the formats of its input signals and control signals. In the figure, l is an input terminal, 2 is a tuning section, 3 is a band amplifier, 4 is an FM demodulator, 5 is an A/D converter, 6 is a digital processing circuit, 7 is a digital image output terminal, and 8 is a band amplifier. , 9 is a control circuit, lO is ■C0111 is a synchronous detection circuit, 12 is a carrier regeneration circuit, 13 is a PSK demodulation output terminal, and 14 is a sample and hold circuit. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] (1) Carrier regeneration used in a receiver that has the function of FM demodulating the video signal and PSK demodulating the PCM audio signal from a composite signal consisting of an FM modulated video signal and a time-division compressed PSK modulated PCM audio signal In the circuit, a voltage controlled oscillator for oscillating a reproduced carrier of the composite signal; a control circuit for controlling the phase and frequency of the output signal of the voltage controlled oscillator during a period in which the composite signal is a PSK modulated signal; During the period in which the composite signal provided between the voltage controlled oscillator and the control circuit is an FM modulation signal, the immediately preceding PS
A carrier regeneration circuit comprising: a sample and hold circuit that holds a stable output signal of the control circuit sampled during the period of the K modulation signal.