JPS5911313B2 - PAL synchronization signal generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a synchronization signal generator for PAL color television system.

Conventionally, in color television systems, the color subcarrier frequency and the horizontal scanning frequency are synchronized with each other.

In the PAL color television system, the red difference signal (
The phase of the signal (RY) is inverted for each horizontal scanning line, and the color subcarrier is quadrature two-phase modulated with the blue difference signal (B-Y).
Through such modulation, the phase distortion in the transmission path is improved, and the color subcarrier frequency (hereinafter referred to as fsc) and the horizontal scanning frequency (hereinafter referred to as fH) are determined to have the following frequency relationship. .

fsc ■ (284-1) fH+ - ...... (1
) 104625 These frequency values have fH of 15625K
H2, and fsc is 4.43MH2 from equation (1).

A synchronizing signal generating device for generating synchronizing signals having each of these frequencies is constructed as shown in FIG. That is,
An fsc signal of 4.43MH2 is generated from oscillator 2,
A frequency signal of a predetermined times (22 times) fH from the multipipulator 4 is subtracted in the mixer 6 .

The output of the mixer 6 is frequency-divided and multiplied by a plurality of frequency divider circuits 8 and a multiplier circuit 10, and is introduced into a phase detection circuit 12 as a signal of a predetermined frequency. Signals of the same frequency obtained by dividing the output of the multipipulator 4 by the frequency dividing circuit 14 are introduced into the phase detection circuit 12, and their phases are compared with each other. The output of the phase detection circuit 12 corresponding to the phase error is introduced as a control signal to the multipipelator 4, and the output of the multipipelator 4 is controlled. In such a synchronizing signal generating device, a plurality of frequency dividing circuits 8 and multiplying circuits 90 and 10 are used in order to maintain the relationship of equation (1), and the circuit configuration is particularly complicated due to the use of the multiplying circuits.

The present invention has been made in view of this point, and provides a synchronization signal generating device with a simplified circuit configuration.

95 In the present invention, the following relationship is derived from the above-mentioned equation (1) and used.

=2×284fH−1F.

+Fv... (2) (Note that Fv is the vertical scanning frequency (50Hz).) As is clear from this equation (2), double Fsc is a predetermined times FH (2 x 284) and It includes a predetermined frequency division (1/2) component and an Fv component.

An embodiment of the present invention will be described below with reference to FIG.

A first signal having a frequency 2×284 times FH is derived from the voltage controlled oscillator 20, and this signal is introduced into the signal generator 24 via the divide-by-2 circuit 22.

From the signal generator 24, a second signal of Fv that is phase-synchronized with the first signal and a third signal of 1/2 fH obtained by dividing FI[ by 2 are derived. In addition, 2fsc shown in equation (2) above
A fourth signal is generated from a reference oscillator 26 and introduced into a first modulator 28 as a modulated wave.

A second signal of Fv from the signal generator 24 is introduced into the first modulator 28, and a fourth signal is modulated by this signal. From the first modulator 28, 2X284fH-
A fifth signal of V2fB is derived and introduced into the second modulator 30 as a modulated wave.

The second modulator 30 receives two signals from the voltage controlled oscillator 20.
A first signal of x284fII is introduced and a fifth signal is modulated by this signal.

A signal having the same frequency (1/2 fH) as the third signal is derived from the second modulator 30, and is compared in frequency with the third signal by a comparator 32. Comparator 32
, a DC voltage corresponding to the frequency difference is detected, and this DC voltage is introduced to the voltage controlled oscillator 20 as a control signal via an amplifier 34.

The output frequency of the voltage controlled oscillator 20 is increased or decreased in response to this control signal. The color subcarrier signal of Fsc is derived from the output of the reference oscillator 26 via a frequency divider circuit 36, and the horizontal scanning signal of Fi[ is derived from the signal generator 24.

Therefore, FsO and FH always have the frequency relationship defined by equation (1) and are derived synchronously. As explained above, according to the present invention, it is possible to use a color toner according to the frequency relationship of equation (2), eliminate the need for multiple multiplier circuits, simplify the circuit configuration, and obtain a compact signal generating device. can.

In addition, in the above-mentioned embodiment, Fv
and a second signal of 2×284 f to the second modulator 30.
Although it has been described that the first signal of H is supplied to each of the H signals, the present invention is not necessarily limited to this. A signal corresponding to the third signal may be derived.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional PAL synchronizing signal generating device, and FIG. 2 is a circuit diagram showing an embodiment of the PAL synchronizing signal generating device according to the present invention.

Claims (1)

[Claims] 1. A voltage controlled oscillator that generates a first signal having a frequency of 2×284 times the horizontal scanning frequency (f_H), and a signal from this oscillator is introduced, and this signal is divided to produce a first signal having a frequency of 2×284 times the horizontal scanning frequency (f_W). a signal generator that generates a second signal having a frequency of 1/2 of the horizontal scanning frequency ((1/2)f_H) and a third signal having a subcarrier frequency ((1/2)f_H);
f_S_C) twice the frequency (2f_S_C=2×28
4f_H−(1/2)f_H+f_V); a fourth signal from the reference oscillator is modulated by the first and second signals;
a modulator that derives a signal of the same frequency as the signal of the third signal; a comparator that compares the frequencies of the signal from the modulator and the third signal to increase a difference component; and means for controlling a first signal frequency of a voltage controlled oscillator.