JPS6059889A - Secam system chrominance signal generating circuit - Google Patents

Abstract

PURPOSE:To obtain a stable signal of the SECAM system by providing a phase locked loop at each chrominance signal system and applying phase lock to one system by means of a chrominance subcarrier signal while the other signal transmits a chrominance signal. CONSTITUTION:A movable contact (c) of changeover switches SW4, SW5 is selected to the position of a contact (a) of a phase locked loop PLLR side, a switch SW3R is opened and a switch SW3B is closed at a time t1. Thus, a signal S3 frequency-modulated by a color difference signal R-Y relating to a chrominance subcarrier signal fR stored in an integration device IR is transmitted from a voltage/frequency converter V/FR at the phase locked loop PLLR side, and the phase of the phase locked loop PLLB is locked at a chrominance subcarrier signal fB. Next, a signal S4 is transmitted at a time t2, the phase of the phase locked loop PLLR is locked by the signal fR. Thus, an output signal S5 shown in (f) and (g) is transmitted repetitively to an output terminal TO.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to a SECAM color signal generation circuit.

(Prior Art) One type of color television system is the 5ECA111 system. This method uses two color difference signals (ny) and (B
-Y) are sent alternately (line sequentially) for each horizontal scan, and are converted into simultaneous signals using a one-line delay line on the receiver side. That is, the first color subcarrier signal fR with a frequency of 4.40625 MH is frequency-modulated with the first color difference signal DR+=-1,9 (ER'-EY') proportional to (RY), and (B -Y) and a second color subcarrier signal fB of frequency 4.25000 MH2 with a second color difference signal DB' = 1.5 (EB'-EY' )
These frequency-modulated color subcarrier signals are alternately multiplexed into a luminance signal via a shaping filter called a Bell filter. Here, ER
The dashes in ', EY'B, and I represent gamma correction.

FIG. 1 is a circuit diagram showing an example of a conventional frequency modulation circuit in the SECAM system, and shows an example configured as a phase-locked loop.

In Fig. 1, two color difference signals (R-Y) and (B-Y) which are applied alternately to the input terminal T every horizontal scan are sent to one input terminal a of the adder ADD via the switch SW1. Added. The other input terminal b of the adder ADD is sW3. The output signal of the phase comparator pc is applied via the low-pass filter LpF and the sample-and-hold circuit SR. The output signal of adder ADD is applied to voltage frequency converter V/F. The output signal of the voltage frequency converter V/F is sent to the output terminal TO and is also applied to one input terminal a of the phase comparator pc. phase comparator p
The first color sub-carrier signal f- and the second color sub-carrier signal fB are selectively applied to the other input terminal of the color sub-carrier signal f- through a changeover switch SW2.

FIG. 2 is an explanatory diagram of the operation of FIG. 1, in which (a) shows the operation of the switch SW, (b) shows the color difference signal S1 applied to the input terminal Ti, and (C) shows the changeover switch SW2. (d) represents the operation of switch SW3. At time to, the switch SW□ is closed, and one input terminal a of the adder ADD receives the color difference signal S□.
(RY) is added, the switch SW3 is opened, and the other input terminal bK of the adder ADD is connected to the first subcarrier signal fR held in the sample-and-hold circuit SH in the previous stage (not shown). signal is added.

In this state, the phase comparator PC is disconnected from the phase locked loop, and the voltage frequency converter V/F is connected to the color difference signal (R-Y
) and the held signal of the sample-and-hold circuit SH, that is, a color signal obtained by frequency-modulating the first color subcarrier signal fR with a color difference signal (RY).

At time t□ when the horizontal flyback section begins, switch SW
1 is opened and the switch SW3 is closed, and the movable contact C of the changeover switch SW2 is connected to the fixed contact C on the side of the second color subcarrier signal -1'. As a result, the phase of the phase B phase-locked loop is locked to the second color subcarrier signal fB. Then, at the time when the horizontal blanking interval ends, the switch SW is closed and the color difference signal 0 is sent to one input terminal color of the adder 1 ADD (L1
2 (n-y) is applied, switches SW, , are opened and the other input terminal of the adder (ADT) is connected to the second color subcarrier signal box held in the sample-and-hold circuit SH. signal is added. As a result, the voltage frequency converter V/F converts the second color into a frequency signal corresponding to the addition signal of the color difference signal (B - Y) and the holding signal of the sample hold circuit SH, that is, the color difference signal (B - Y). subcarrier signal f
A color signal obtained by frequency modulating B is sent out. At time t3 when the next horizontal retrace interval begins, switch SW1 is opened and switch SW3 is closed, and movable contact C of changeover switch SW2 is connected to fixed contact a on the side of first color subcarrier signal fR. Ru. Due to this K., the phase of the phase-locked loop is locked to the first color subcarrier signal fR. Then, at time t4 when the horizontal flyback section ends, switch SW□ is closed and switch SW is opened, and henceforth, time t. The same series of operations will be repeated from then on.

However, according to such a conventional configuration, in order to align the phase at the start of color signal transmission to a predetermined phase, the color subcarrier of the first color subcarrier signal fB or M2 is transmitted within a horizontal retrace interval of approximately 101 Js. It is necessary to lock the phase of the phase-locked loop with the signal fR, and it is necessary to configure a phase-locked loop with fast settling. This has the disadvantage that the configuration of the low-pass filter LPF constituting the phase-locked loop becomes complicated. In addition, in order to increase the phase stability at the start of color signal transmission, the voltage frequency converter V/
This has the disadvantage that the operation of V/F must be stopped and restarted, and the configuration of the voltage frequency converter V/F becomes complicated.

(Objective of the Invention) The present invention has been made with attention to these points, and its object is to provide a stable SECA with a relatively simple configuration.
An object of the present invention is to provide a signal generation circuit that can obtain an M-type color signal.

(Summary of the Invention) The present invention achieves the above object by providing a phase-locked loop for each raw color signal system, and in a high state in which one phase-locked loop sends out a color signal, the other phase-locked loop is connected to that loop. The assigned color subcarrier □ It is characterized by being phase-locked with the transmitted signal.

(Example) Hereinafter, it will be explained in detail using the drawings.

FIG. 3 is a circuit diagram showing an embodiment of the present invention, w
, parts equivalent to those in Figure 1 are given the same reference numerals. In FIG. 3, two color difference signals (R-Y) and (B-Y) are applied alternately to the input terminal Ti every horizontal scan. These color difference signals are applied to one input terminal a of one adder ADDR through a changeover switch sw4 which is switched every horizontal scan, and one color difference signal (It-Y) is applied to one input terminal a of one adder ADDR.
The other color difference signal (B-Y) is applied to one input terminal 8 of the other adder ADDB.

The other input terminal of one adder ADDR is a switch SW3. which is opened or closed every horizontal scan. The output signal of the phase comparator PcR is added via an integrator. The output signal of this adder ADDR is transmitted to the voltage frequency converter V
/FR, the output signal s3 of the voltage frequency converter V/F is applied to one input terminal aK of the phase comparator PcR, and is passed through a changeover switch SW5 which is switched in conjunction with the changeover switch SW4 every horizontal scan. output terminal T
o. A first color subcarrier signal fR is applied to the other input terminal of the phase comparator pCR. The other input terminal of the other adder ADDB is connected to the switch 5w3.
A switch sw that is complementary to R and is closed or opened every horizontal scan.

B The output signal of the phase comparator pcB is added via the integrator 8. The output signal of this adder ADDB is applied to the voltage frequency converter vlFB, and the output signal s4 of the voltage frequency converter V/M is applied to one input terminal a of the phase comparator pcB.
lc is applied to the output terminal To via the aforementioned changeover switch SW5. A second color subcarrier signal fB is applied to the other input terminal bK of the phase comparator PCB. That is, in FIG. 3, the first color subcarrier signal fR
9 Phase comparator pcR, integrator □, adder ADDR and voltage frequency converter v/FR form the first phase locked loop PL.
LR is configured, and a second phase locked loop PLLB is configured by a second color subcarrier signal fB1, a phase comparator pcB, an integrator IB, an adder ADDB, and a voltage frequency converter v/FB. This allows one voltage frequency converter vlF
From R, the first signal is frequency-modulated by the color difference signal (n - Y).
The color subcarrier signal fR is sent out as the color signal S3, and the color difference signal (B - Y
), the second color subcarrier signal fB frequency-modulated is sent out as a color signal S4.

FIG. 4 is an explanatory diagram of the operation of FIG. 3, in which (11) represents the color difference signal S1 applied to the input terminal T1, and (b)
represents the operation of the switch 5W3R, (C) represents the operation of the switch 5W3B, and (d) represents the operation of the voltage frequency converter V.
/FR represents the frequency change of the output signal S3, (e) represents the frequency change of the output signal S4 of the voltage frequency converter V/F, and (f) represents the frequency change of the output signal S5 sent to the output terminal TO. 2 represents a frequency change and shows an example of the waveform of the output signal S5 sent to the output terminal TO. At time 1, the movable contact C of changeover switch sw, SW5 is switched and connected to the fixed contact a on the first phase-locked loop PLLR side, switch SW3 is retracted and opened, and switch 5w3B is connected.
is closed. As a result, the voltage-frequency converter V/FR on the side of the first phase-locked loop pLLR converts the signal related to the first color subcarrier signal fIIK held in the integrator into a color difference signal (R-Y). A frequency-modulated signal s3 is sent out, and the second phase-locked loop pLLB is phase-locked with the second color subcarrier signal fB.

This state occurs at time t2 when one horizontal period section ends.
During this period, the output phase of the voltage-frequency converter vlFB of the second phase-locked loop pLLB is sufficiently stabilized. At time t2 when the next horizontal cycle section begins, selector switch sw4. The movable contact C of sw5 is switched and connected to the fixed contact bK on the second phase-locked loop PLLB side, the switch 5w3R is closed, and the switch S)v is opened. As a result, the voltage-frequency converter vlFB on the side of the second phase B locked loop PLLB converts the signal related to the second color subcarrier number fB held in the integrator into a color difference signal (B-Y). A frequency modulated signal S is sent out to the first phase-locked loop PLLR.
When the phase is locked with the color subcarrier signal fR, the result is .

This state occurs at the time t when this horizontal period section ends.
3, and the output phase of the voltage frequency converter V/FR of the first phase-locked loop PLL unit is sufficiently stabilized during that time. Then, the time t when the next horizontal periodic section starts
At step 3, the state returns to the same state as at time t1, and the same operation is repeated thereafter. As a result, the output signal S5 as shown in FIGS. 4(f) and (g) is repeatedly sent to the output terminal To.

According to such a configuration, the phase at the start of sending is stabilized without temporarily stopping the operation of the stain pressure frequency converter, which performs the phase opening of the phase-locked loop in the horizontal retrace interval as in the past. Color signals can be obtained. In addition, since a phase-locked loop is configured for each color subcarrier signal, each phase-locked loop can be designed according to each color subcarrier signal.
Compared to the conventional case in which both color subcarrier signals are used in common, components can be relatively inexpensive, and the overall circuit configuration can be simplified.

In addition, although the above embodiment shows an example in which an integrator is used in the phase-locked loop, a combination of a low-pass filter and a sample-and-hold circuit may be used.

(Effects of the Invention) As described above, according to the present invention, it is possible to realize a signal generation circuit that generates stable SECAM color signals with a relatively simple configuration.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing an example of a conventional circuit, and Figure 2 is a circuit diagram showing an example of a conventional circuit.
3 is a circuit diagram showing an embodiment of the present invention, and FIG. 4 is an explanatory diagram of the operation of FIG. 5. T1...input terminal, TO...output terminal, ADD...
・Adder, V/F...voltage frequency converter, PC...
Phase comparator, ■... Integrator fRT fB... Color subcarrier signal, SW3... Switch, SW, SW5.
...Choice switch.

Claims (1)

[Claims] The first color subcarrier signal frequency-modulated with the (R-Y) color difference signal and the second color sub-carrier signal frequency-modulated with the (B-Y) color difference signal are alternately used for each horizontal scan. In a 5ECAlil color signal generation circuit configured to send out a color signal, a phase-locked loop is provided for each color signal system, and when one phase-locked loop is sending out a color signal, the other phase-locked loop is connected to that loop. A 5ECA λ1 type color signal generation circuit characterized in that a phase shift is performed using an assigned color subcarrier signal.