JP2577817B2 - SECAM Identifier - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a SECAM ident detection device used in, for example, a SECAM color television receiver.

[Conventional technology]

In SECAM color signal processing, the SECAM color signal is 1
The color difference signals of BY and RY are FM-modulated and transmitted to the subcarriers of 4.25 MHz and 4.40625 MHz, respectively, in each horizontal period (hereinafter 1H). Therefore, 1H every 1H using 1H delay line
By switching between signals that pass through the delay line and signals that do not pass through, normal BY and RY signals are reproduced. In order to perform this switching normally, an ident detection is performed.

FIG. 3 shows a conventional SECAM identity detection device. In the figure, 1 is an FM detector for detecting an ident, 2, 3, 4, 5, 6,
7 is an NPN transistor constituting a double-balanced multiplier, 8 is a constant current source, 9 and 10 are load resistors, 11 is a power supply terminal, 1
2, 13 is a switching pulse input terminal for each 1H, 14 is a sample and hold circuit, 15 is a hold capacitor, 16 is an identity detection comparator, 17 is a killer detection comparator, 18, 19,
Reference numeral 20 denotes a power supply voltage divided by a resistor to create a reference voltage for identification and killer detection, reference numeral 21 denotes a killer output terminal, and reference numeral 22 denotes an identification output terminal.

 Next, the operation will be described.

The FM detector 1 for detecting an ident is usually a resonance circuit having a high Q in order to increase the killer and ident detection sensitivity. First, the principle of the case where the resonance circuit is adjusted to a regular position will be described.

FIG. 4 (a) shows the waveform at point A. As shown in the figure, the detection outputs of the RY and BY line bursts are output so as to be vertically symmetrical about the no-signal DC voltage. At point D, an inverted waveform of the waveform at point A is output.
This waveform is input to a few differential pairs. On the other hand, when the ident is detected normally, the waveform shown in FIG. 4B is output from the flip-flop (hereinafter referred to as F / F) at point B, and this waveform is composed of 3, 4, and 6, 7. Differential pair every 1H
A few collector currents are switched and supplied to the load resistor. The waveform at the point C is as shown in FIG. 3C, and the line burst is always higher than the no-signal DC voltage. This line burst voltage is stored in the hold capacitor 15 by the sample and hold circuit 14. This voltage is used as a killer detection comparator
The voltage is compared with the killer detection voltage at 17 and becomes higher than the killer detection voltage in this case, and the killer output 21 becomes low. In addition, since the voltage is higher than the ident detection voltage, the ident detection comparator 16 goes low, and the state is maintained.

If the F / F operates in a state where the waveform of FIG. 3 (b) is inverted, the waveform of FIG. 3 (c) is inverted. Becomes lower than the ident detection voltage, the outputs of the output terminals 22 and 21 become Hi, and the F / F circuit is stopped at this time. In other words, point B is fixed at High and point E is fixed at Low. The waveform at point C is output symmetrically up and down every 1H. If this is sampled and held, it becomes equal to the no-signal DC voltage. Will rise, and when it becomes higher than the ident detection voltage, the F / F
Starts working again. At this time, if the direction is normal, the voltage of the capacitor 15 rapidly rises and returns to the normal voltage. This is the identity operation, and this operation is always performed at the time of channel switching or power-on, and a normal color is reproduced.

Next, considering a case where the center frequency of the resonance circuit used in the FM detector 1 for detecting an ident is slightly shifted, the waveform at the point A is shown in FIG. Thus, the output is small at RY and BY is large. At this time, the F / F in FIG.
In the case of an output, the point C is as shown in FIG. 7 (f), but the voltage of the capacitor 15 is still higher than the killer detection voltage and still operates normally. However, if the F / F output is inverted at the time of channel switching, the voltage of the capacitor 15 drops, and the identity detection voltage also drops, so that the F / F is stopped. T ₁ subsequent point B waveform in FIG. (G) represents that the stop is lowered F / F than voltage Aidento detection voltage of the capacitor 15. FIG. 11H shows the waveform at point C in this state. t ₁ but thereafter becomes the same waveform as the (d) of FIG Since F / F is stopped, B-Y voltage of the capacitor 15 for a large amplitude of stopping low F / F than Aidento detection voltage In this state, it stops in this state, and does not return to normal.

Fig. 5 shows the center frequency of the resonant circuit and the range in which the ident operates normally. Compared with the range in which the coil is turned from the normal state and the killer operates, the normal operation is possible even if the F / F is reversed. The range of the return is asymmetric on the frequency axis, and in this case, the margin is reduced at the upper frequency.

[Problems to be solved by the invention]

Since the conventional SECAM identity detection device is configured as described above, there is no margin on one side for any of the center frequencies of the resonance circuit, and if the center frequency of the resonance circuit shifts due to temperature change, the However, there is a problem that it malfunctions.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to obtain a SECAM ident detection device having a wide frequency range in which an ident operates normally.

[Means for solving the problem]

The SECAM ident detection device according to the present invention is configured to stop the F / F while the ident detection output is Hi, and to sample and hold the non-signal DC voltage.

[Action]

Since the SECAM ident detection device in the present invention stops the F / F at the ident detection output and switches the hold capacitor to the non-signal DC voltage,
The ident operation is reliably performed.

〔Example〕

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

FIG. 1 shows a SECAM identity detection device according to an embodiment of the present invention. In the drawing, the same reference numerals as those of the conventional device denote the same parts. In the figure, 23 and 24 are NPN transistors,
The emitter and base are connected in common, and the emitter is
The emitters are connected to a few emitters, the base is connected to an identity detection output 22, and the collectors are connected to load resistors 9 and 10, respectively.

 Next, the operation will be described.

A case where the center frequency of the resonance circuit is shifted as described above will be described. FIG. 2 (a) shows the waveform at point A. In this case, if the F / F in channel switching or the like is reversed gradually decreases the voltage of the capacitor 15, the output becomes Hi output terminal 22 is lower than Aidento detection voltage at the time of t _1,
At the same time as the F / F is stopped, the NPN transistors 23 and 24 are turned on, and the current of the constant current source 8 flows half through the load resistors 9 and 10 without passing through the transistors 2 to 7. Therefore, the same voltage as the no-signal DC voltage is generated at the point C as shown in FIG. Moreover, this voltage is always constant regardless of the center frequency of the resonance circuit, and is always set higher than the ident detection voltage and lower than the killer detection voltage. Since the voltage becomes higher than the detection voltage and the F / F stop can be released, the F / F does not stabilize in a stopped state. When the ident detection output returns to low, the NPN transistors 23 and 24 are cut off, and the transistors 2 to 2 are again turned on.
The double-balanced multiplier 7 starts its operation, and at this time, if the F / F is in a normal state, it returns quickly. T ₂ in FIG. (B) is gradually voltage of the capacitor 15 rises, indicates a point when a higher than Aidento detection voltage.

In the above embodiment, the no-signal DC voltage is obtained by operating the transistor switch. However, the circuit for obtaining the no-signal DC voltage is not limited to such a circuit, and the F / F is stopped. At the same time, any type may be used as long as the voltage applied to the sample and hold circuit can be the non-signal DC voltage.

In addition, the present invention is not limited to television, but can be applied to any device that demodulates SECAM signals, and has the same effects as described above.

〔The invention's effect〕

As described above, according to the present invention, the F / F is stopped while the ident detection output is set to Hi and switched to the non-signal DC voltage at the same time.
There is an effect that a device that operates stably can be obtained at low cost.

[Brief description of the drawings]

FIG. 1 is a diagram showing a SECAM identity detection device according to one embodiment of the present invention, FIG. 2 is a waveform diagram for explaining the operation thereof, FIG. 3 is a diagram showing a conventional SECAM identity detection device, FIG. FIG. 5 is a waveform diagram for explaining the operation of the conventional example, and FIG. 5 is a diagram showing an ident operation range with respect to the center frequency of the conventional resonance circuit. In the figure, 1 is an FM detector for detecting an ident, 2 to 7 are double-balanced multipliers, 9 is a load resistor, 14 is a sample and hold circuit, 15 is a capacitor, 16 is a comparator for detecting an ident, and 23 and 24 are This is a transistor switch for obtaining a no-signal DC voltage. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] An output of a differential amplifier connected to an output of an identity detection FM detector for detecting a line burst is switched every horizontal period by a signal having a half of a horizontal frequency obtained by dividing a frequency by a flip-flop. The load is R-
The same polarity is always obtained in both Y and BY, the output voltage generated in the load is stored in a capacitor by a sample and hold circuit, and the voltage stored in the capacitor is compared with a reference voltage.
When detecting inversion, the SECAM ident detection device is configured to stop the flip-flop in one direction and at the same time switch the output voltage generated at the load to a voltage higher than the reference voltage.