JPS6017986Y2 - Color signal processing circuit for color television receivers - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a color television receiver capable of receiving two broadcast signals, PALa and NTSC signals.

For example, if a videotape recorded with an NTSC VTR is
When playing on an AL VTR, the color subcarrier is 4.43.
A MHz NTSC signal is obtained.

In order to receive this signal on a PAL color television receiver, a color signal processing circuit that can process the 4.43 MHz NT'sC signal is required.

In addition to this example, 3.58 MHz PAL
Since there are some areas where PAL and NTSC signals are broadcast, a color television receiver that can receive both PAL and NTSC signals is desired.

Figure 1 briefly shows the general configuration of a PAL color signal processing circuit, in which a carrier color signal obtained from a video intermediate frequency signal is amplified by first and second bandpass amplifiers 1 and 2. Ru.

On the other hand, the burst signal gated by the burst gate circuit 10 acts as a reference signal for phase detection of the oscillation signal of the color subcarrier oscillator 12 in the APC (automatic phase control) phase detector 11. The output of serves as a phase control for the color subcarrier oscillator 12.

The carrier color signal output from the second bandpass amplifier 2 is I
H (one horizontal period) is supplied to the adder 5 and the subtracter 6 through both the delay line 3 and the non-delay path 4.

Adder 5 performs addition of carrier color signals applied through IH delay line and non-delay path 4.

As a result, in the adder 5, the R-Y component of the carrier color signal is canceled out, and the B-Y component is output with twice the magnitude.

This output is given to the BY demodulator 7 at the next stage.

On the other hand, the subtracter 6 subtracts the carrier color signals given from the IH delay line 3 and the non-delay line 4, cancels the B-YJi component, and doubles the R-Y component (this R-y component is inverted for each IH) and supplied to the next stage RY demodulator 8.

The color subcarrier generated by the color subcarrier oscillator 12 is 90
The signal is supplied to the BY demodulator 7 through the .degree. phase shifter 13, and is also supplied to the RY demodulator 8 through the PAL switch 14, which switches 180.degree. every IH.

The PAL switch 14 is connected to the modulation axis of the R-y component, whose modulation axis is inverted for each line among the PAL carrier color signal components, and the demodulation axis in the R-Y demodulator 8 [color subcarrier oscillator 12 This switch is used to match the phase with the carrier wave] and is considered essential in standard PAL color television receivers.

B-Y demodulator? , B-Y demodulated by the R-Y demodulator 8,
The R-Y color difference signal is used in the matrix circuit 9 to create a G-Y color difference signal and is output individually.

For such a PAL color signal processing circuit as shown in Fig.
The C color signal processing circuit corresponds to the circuit in FIG. 1 from which the IH delay line 3, adder 5, subtracter 6, and PAL switch 14 are removed.

Therefore, it goes without saying that when an NTSC color signal is input to the circuit shown in FIG. 1, normal demodulation cannot be performed because the phase of the RY signal is not inverted for each IH.

Therefore, it is necessary to separately provide a circuit for NTSC color signal processing, but this means that the number of circuit configurations increases, which is not economical.

The present invention is designed to process PAL and NTSC color signals in a single color signal processing circuit, particularly with respect to the carrier color signal supplied to the demodulator.

This paper proposes a color signal processing circuit in which the adder/subtractor circuit is modified in a certain way so that there is no problem in receiving any NTSC signal.

The present invention will be described in detail below according to embodiments shown in the drawings.

FIG. 2 specifically shows the addition/subtraction circuit and its related circuits in the color signal processing circuit implementing the present invention. The same parts as in FIG.
a transistor to the base of which the carrier color signal from the bandpass amplifier 2 is applied via a coupling capacitor C2;
Its collector is connected to a +12V power supply line 16 via a parallel circuit of a coil L and a resistor 9, and a volume VR.
Both ends of the parallel circuit are connected to input terminals of the IH delay line 3.

On the other hand, the base is biased by voltage dividing resistors R□ and R2, and the emitter is resistors R3 and R.

is connected to ground by a bypass capacitor C2 and a resistor #s, a diode D1 and a bypass capacitor C3.
A gain changing means is added.

This gain changing means will be described later.

The output of the IH delay line 3 is connected to a transformer T that constitutes an addition/subtraction circuit.
The secondary coil L2 is connected to the primary coil L□, one end of the secondary coil L2 is connected to the B-Y demodulator 7, the other end is connected to the R-Y demodulator 8, and the middle point of the secondary coil h is connected to the It is connected to the movable terminal of the volume VR to supply a non-delayed carrier color signal to its midpoint.

A collector-emitter path of a switching transistor Tr2 is connected together with a DC blocking capacitor between the midpoint and a reference potential point (earth point in the illustrated case), and a base of the switching transistor Tr2 is connected to a bleeder resistor.

, R3 to the received signal amount detection circuit 15.

This received signal detection circuit 15 has the number of horizontal synchronizing signals of PAL.
Focusing on the difference between 62 sync signals and NTSC 52 sync signals, the system is configured so that when the number of synchronization signals is 625, it produces an OV output, and when it is 525, it produces a +12V DC output. has been done.

Therefore, when receiving a PAL signal, only QV is applied to the base of the switching transistor Tr2, so the switching transistor Tr2 is turned off, and the non-delayed carrier color signal applied through the non-delay path 4 is not invalidated but is It is supplied to the middle point of the next coil L2,
It is combined with the delayed signal from the primary coil L1.

The lH delayed carrier color signal applied to the secondary coil L1 is induced at one end A and the other end of the secondary filter L2 with mutually opposite polarities, and is added to the non-delayed carrier color signal on the A side and subtracted on the mouth side. It will be.

Next, in the case of NTSC signal reception, the +12V output from the received signal detection circuit 15 is set to 19. Since the positive voltage divided by R8 is applied to the base of the switching transistor Tr2, the switching transistor Tr2 becomes conductive, and the non-delayed carrier color signal from the non-delay path 4 is grounded through the collector-emitter path of the transistor Tr2. It is dropped and becomes invalid.

In such a state, no problem occurs because the IH delayed signal induced across the secondary coil of the transformer T is supplied as is to the BY demodulator 7 and the RY demodulator 8.

If the non-delayed carrier color signal is not invalidated by the switching transistor Tr2 when receiving the NTSC signal, the delayed carrier color signal will be subtracted from the delayed carrier color signal at the other end of the secondary coil L2, resulting in the delayed and non-delayed carrier color signals. They will cancel each other out (because in NTSC, the carrier color signals are in phase regardless of whether they are delayed or not), and the R-Y demodulator 8 will not be supplied with substantially any carrier color signals.

'In addition, as mentioned above, since the non-delayed signal is invalidated and only the delayed signal is supplied to the B-Y demodulator 7 and the R-Y demodulator 8, the difference between the delayed carrier color signal and the non-delayed carrier color signal is There is an inconvenience that the carrier color signals supplied to the demodulators 7 and 8 are smaller than when receiving PAL signals that are synthesized and supplied to the demodulators 7 and 8. In the embodiment shown in FIG. 2, it is added.

That is, by adding the output of the received signal detection circuit 15 to the diode D provided at the emitter of the transistor Tr□, the NTS
When receiving a C-system signal, the diode D is made conductive and the resistor R5 is added in parallel as an emitter resistance to reduce the combined emitter resistance of the transistor Tr□, thereby reducing the amount of negative feedback, thereby increasing the gain of the transistor Tr□. That's how I do it.

In this way, by increasing the gain of the transistor Tr1 when receiving a signal of the NTSC method than when receiving a signal of the PAL method, the magnitude of the carrier color signal supplied to the demodulators 7 and 8 can be changed between the signal reception of the PAL method and the NTSC method. This means that the signals are uniformly received.

In the above-mentioned FIG. 2, it goes without saying that the configuration may be such that a non-delayed signal is added to the primary film side of the transformer T and a delayed signal is added to the intermediate tap of the secondary coil L2. The delayed signal is nullified by the switching transistor Tr2, and the non-delayed signal is sent to the demodulators 7 and 8.
supplied to

FIG. 3 shows another embodiment of the present invention, and the same parts as in FIG. 2 are given the same symbols for convenience of explanation.

The circuit in Figure 3 differs from the circuit in Figure 2 in that the switching transistor Tr2 is inserted between the input terminal of the primary coil h of the transformer T and the ground, and therefore the NTSC
It is the delayed signal that is invalid when receiving the signal of the method.
The demodulators 7, 8 are supplied with non-delayed signals.

As described above, according to the color signal processing circuit of the present invention, NTSC
When receiving a PAL signal, either the IH delayed or non-delayed carrier color signal is preferably disabled.
Carrier color signals can be supplied to the B-Y and R-Y demodulators as desired when receiving signals in both the NTSC and NTSC systems.

Moreover, the amplification degree of the amplifying transistor for the delayed or non-delayed carrier chrominance signal is switched to increase when receiving the NTSC signal, and the magnitude of the carrier chrominance signal supplied to each of the demodulators is changed to the PAL signal. It is equalized when receiving a signal and when receiving an NTSC signal.

Therefore, there is no need to change the internal or peripheral circuit configuration of each of the above demodulators from the conventional one, and therefore, it is possible to use a general-purpose FA.
I, color signal processing IC can be used, FAI, /NTSC
A color television receiver capable of receiving NTSC system reception can be realized at low cost.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the general configuration of a PAL color signal processing circuit. FIG. 2 is a circuit diagram of a main part of a color signal processing circuit of a color television receiver embodying the present invention, and FIG. 3 is a circuit diagram of a main part showing another embodiment of the present invention. T...Transformer, 3...IH delay line,
7...B-Y demodulator, 8...R-Y demodulator, Tr2...Switching transistor.

Claims (1)

[Scope of utility model registration request] One of the IH delayed or non-delayed carrier color signals inputted through the amplifying transistor is applied to the primary coil of the transformer to induce mutually opposite polarities at both ends of the secondary coil, and at the same time, a A PAL in which the other of the carrier color signals is applied to the tap, the addition output generated at one end of the secondary coil is supplied to the B-Y demodulator, and the subtraction output generated at the other end is applied to the R-Y demodulator. In the color signal processing circuit, a first switching element is connected between the input end of the secondary coil or the intermediate tap of the secondary coil and a reference potential point, and a second switching element for switching the amplification level is connected to the amplification transistor. When receiving a signal in the NTSC system, the first switching element is made conductive to invalidate one or the other carrier color signal, and the second switching element changes the amplification degree of the transistor to the NTSC system. The magnitude of the carrier color signal given to each demodulator is increased when the PAL signal is received.
A color signal processing circuit for a color television receiver that equalizes signals when receiving NTSC and NTSC signals.