JPS6225317B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal discrimination circuit suitable for use as a SECAM switch verification circuit in a SECAM type color television receiver.

As is well known, the SECAM system uses two different color signal information, the (B-Y) signal and the (R
-Y) The signal is in the form of frequency modulation of each carrier wave.
It is transmitted line-sequentially alternately every horizontal period. On the receiver side, 1 is converted into a simultaneous signal by a horizontal periodic delay line and a switching circuit called SECAM switch, and the (B-Y) signal is sent to the (B-Y) demodulator (R
-Y) signals are respectively supplied to (RY) demodulators to reproduce color signals. This SECAM switch is driven by the output of a flip-flop circuit that is inverted every horizontal period, and is matched to control the phase of the flip-flop circuit correctly according to the color signal input in order to supply the correct color signal to each demodulator. circuit is required.

The color signal of the SECAM method is the (B-Y) signal.
By frequency modulating the 4.25MHz carrier wave, (RY)
The signal is transmitted line-sequentially by frequency modulating a 4.40 MHz carrier wave, but unmodulated carrier waves of 4.25 MHz and 4.40 MHz are inserted as discrimination signals at the beginning of each horizontal period signal. The above verification circuit detects the correct phase state of the flip-flop circuit by extracting this discrimination signal and determining its frequency, and if the phase is incorrect, it resets the flip-flop circuit to return it to the correct state. going through the motions.

An object of the present invention is to provide a signal discrimination circuit for operating this collation circuit reliably.

According to the present invention, in a color television signal receiving circuit in which two color discrimination signals are transmitted line-sequentially as carrier waves with different frequencies for each scanning line, the two color discrimination signals are frequency-discriminated and differential signals are transmitted. An FM detection circuit extracts the output current, supplies one first output current of the differential output current to the commonly coupled emitter of the first transistor and the second transistor, and supplies the other second output current to the third output current. the commonly coupled emitters of the first transistor and the fourth transistor, the commonly coupled bases of the first transistor and the fourth transistor, the second transistor and the third transistor;
A control signal that is inverted every scan line is applied between the commonly-coupled bases of the first transistor and the common-coupled base of the transistor. A signal comprising: a transistor differential switch circuit for extracting a fourth output current from the commonly coupled collectors of the four transistors; and means for extracting a current as a difference between the third output current and the fourth output current as a discrimination output current. Obtain a discrimination circuit. Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an operational principle diagram for explaining the operation of the signal discrimination circuit according to the present invention. The FM detection circuit 1 shown as a block has a differential amplification configuration and can extract detection output currents with mutually opposite phases, and the input terminal 2 has a color signal input including a discrimination signal.
It is applied as an FM detection input, and a gate pulse is applied to the gate terminal 3 for extracting the discrimination signal. The FM detection circuit 1 detects the discrimination signal only during the gate pulse period applied to the gate terminal 3, and extracts the detection output currents I ₀₁ and I ₀₂ .

FIG. 2 is a characteristic diagram for explaining the operation of the FM detection circuit 1, in which the detected output current is expressed as I ₀₁ shown by a solid line and I ₀₂ shown by a broken line with respect to the input signal frequency. The detection output current at two discrimination signal frequencies ₁ and ₂ is such that the detection output current I ₀₁ at discrimination signal frequency ₁ and the detection output current I 02 at discrimination signal frequency ₂ are equal (I ₀ + i), and the detection output current I ₀₂ at discrimination signal frequency ₂ is equal to The detection output current I ₀₁ and the detection output current I ₀₂ at discrimination signal frequency ₁ are equal (I ₀
-i), the detection characteristics of the FM detection circuit 1 shown in FIG. 1 are set by adjusting the phase shift circuit 4. In FIG. 1, transistor 5,
6, 7, and 8 are the detection output current I ₀₁ of the FM detection circuit 1.
This is a differential switch circuit that switches _I02 every horizontal period (abbreviated as one line), and is driven by the output signal of the flip-flop circuit that drives the SECAM switch. The bases of transistors 5 and 8 are connected in common and the output signal of one of the flip-flop circuits is applied, the bases of transistors 6 and 7 are connected in common and the output signal of the other is applied,
Transistors 5 and 8 and transistors 6 and 7 are alternately turned on for each line. transistors 5 and 6
The emitters of are connected in common and the detection output current I ₀₁
is supplied, and the emitters of transistors 7 and 8 are commonly connected to supply a detection output current _I02 . Further, the collectors of transistors 5 and 7 are commonly connected to the collector of transistor 9, and the collectors of transistors 6 and 8 are commonly connected to transistor 10.
connected to the collector. The bases of transistors 9 and 10 are connected to the collector of transistor 9, and the emitters of transistors 9 and 10 are connected to terminal 11 to which a power supply voltage is supplied, forming a constant current load. Therefore, transistor 6,
If the common connection point of collectors 8 and 10 is the output terminal 12, the discrimination output current I flowing out from the output terminal 12 is equal to the difference between the detection output currents I ₀₁ and I ₀₂ in one line where transistors 5 and 8 are conductive. I ₀₁ - _{I 02} , and transistors 6 and 7 are conductive 1
In the lines, the difference between the detection output currents I ₀₁ and I ₀₁ is I ₀₂ −I ₀₁ , and the detection output current of the discrimination signal obtained by the FM detection circuit 1 is output as a differential output with the polarity inverted for each line. FIG. 3 is a signal waveform diagram for explaining the circuit operation of FIG. 1, and FIG. 3A is a signal waveform diagram for explaining the circuit operation of FIG.
Shows SECAM color signal. As mentioned above, in the SECAM color signal, a discrimination signal with a different frequency for each line is inserted at the beginning of the color signal of each line.
₁ = 4.25MHz, ₂ = 4.40MHz.
Figure 3B shows the detection output current shown in Figures 1 and 2.
It represents I ₀₁ , and I ₀ +i or I ₀ -i is passed only during the discrimination signal period by the gate pulse.
Similarly, FIG. 3C shows the detected output current _I02 . Here, the flip-flop output signal shown in FIG. 3D is supplied to the bases of transistors 5 and 8 in FIG.
_{When the} discrimination output current I _{is added} to the base _of When is ₂ , I = I ₀₂ - I ₀₁ = (I ₀ + i) - (I ₀ - i) = 2i, and the difference current output during the discrimination signal period is +2i, and the third
It can be expressed as shown in Figure E. Also, the phase of the output signal of the flip-flop circuit is inverted, that is, the third
Conversely, if the signal in Figure D is applied to the base side of transistors 6 and 7 in Figure 1, the discrimination signal frequency is ₁ .
When I=I ₀₂ −I ₀₁ =(I ₀ −i)−(I ₀ +i)=−2i,
₂ , I=I ₀₁ −I ₀₂ =(I ₀ −i)−(I ₀ +i)=−
2i, resulting in the discrimination output current shown in FIG. 3F.
In addition, when the flip-flop is stopped, the current difference between B and C in Figure 3 becomes the discrimination output current +2i
and -2i will flow alternately on each line.

Furthermore, consider the case where the PAL color signal shown in FIG. 3G is added as an input signal. The PAL color signal is a 4.43MHz carrier wave that is repeatedly sent as a burst signal to the part corresponding to the discrimination signal of the SECAM color signal, and this is almost equal to the SECAM discrimination signal frequency ₂ = 4.40MHz, so the detection The output currents are constant as I ₀₁ =I ₀ -i and I ₀₂ =I ₀ +i for each line, and the discrimination output current I becomes the current shown in FIG. 3H in which -2i and +2i alternately flow for each line. Also,
If the signal level of the input color signal decreases, the value of the detection output current i naturally decreases, and in a no-signal state, the discrimination output current I=0.

As described above, according to the signal discrimination circuit according to the present invention shown in FIG. 1, when the line sequential phase of the SECAM color signal and the output signal phase of the flip-flop circuit are correct, when the output signal phase is opposite, , when the flip-flop stops, and when a PAL color signal is input, all of which can be detected as a difference in the discrimination output current. FIG. 4 is a circuit connection diagram showing one embodiment of the present invention, and the same reference numerals are used for parts corresponding to those in FIG. 1. Transistors 13, 14, 15, 16, 17 and capacitor 1
8, 19, 20, 21 and resistors 22, 23, 24
The circuit constituted by this circuit corresponds to the FM detection circuit 1 in FIG. 1, and a chrominance signal is supplied as an FM detection input signal from a chrominance signal amplification stage 25 to one end of capacitors 18, 19, 20, and 21. A phase shift circuit 4 is connected to the bases of the transistors 13 and 16, and resistors 22 and 2
A base bias voltage is applied from a bias terminal 26 via 3. The transistor 17 has its base connected to the gate terminal 3 to which a gate pulse is applied, and operates as a current supply source for the emitter current 2I ₀ of the differential transistors 14 and 15. The collector current of transistor 14 becomes a detection output current corresponding to I ₀₁ in Fig. 2 depending on the frequency of the input signal, and the collector current of transistor 15 becomes a detection output current corresponding to I ₀₂ in Fig. 2, which is used for FM detection. going through the motions. Transistors 5, 6, 7, and 8 are the same differential switch circuits as shown in FIG. 1, and each transistor has a flip-flop circuit 2 at its base.
7, an output signal that is inverted every line is applied. Transistors 9 and 10 also form a constant current load and supply a discrimination output current to output terminal 12. A load resistor 28 is connected to a bias voltage source 29 to the output terminal 12, and as the discrimination output current flows through the load resistor 28 to the bias voltage source 29, a discrimination output voltage proportional to the amount of discrimination output current is generated. can get. A sampling circuit consisting of transistors 30 and 31 and resistors 32 and 33 is further connected to the output terminal 12. The emitters and collectors of the transistors 30 and 31 are connected to each other, and the bases of each are connected to the resistor 32. 33 to a sampling pulse input terminal 34. Further, one of the emitter-collector coupling parts of the transistors 30 and 31 is connected to the output terminal 12, and the other is connected to the hold capacitor 35 and the hold output terminal 36.
connected to. A sampling pulse is applied to the sampling input terminal 34 so as to make the transistors 30 and 31 conductive only during the discrimination signal period, and the discrimination output voltage obtained at the output terminal 12 is supplied to the hold capacitor 35, and the output voltage is applied during the sampling period. Charge the battery. During the period when no sampling pulse is applied, the transistors 30 and 31 are cut off, and the voltage charged in the hold capacitor 35 is held, and the peak value of the discrimination output voltage becomes a DC voltage and is output to the hold output terminal 36. It can be done. Therefore, as described in the explanation of FIG. 1, the discrimination output current I detected according to the state of the color signal input
can be extracted by converting it into a DC voltage, so for example, when the discrimination output current I=2i, the voltage is higher than the bias voltage source 29, when I=--2i, the voltage is lower than the bias voltage source 29, and when 2i and -2i alternately flow or when I=0, bias voltage source 2
The voltage of 9 is obtained as is at the hold output terminal 36. By extracting the output of the signal discrimination circuit according to the present invention as a voltage in this manner, the above-mentioned SECAM switch verification circuit can be constructed, and the phase state of the flip-flop circuit can be maintained correctly.

It also detects the presence or absence of the SECAM discrimination signal, the reception of the PAL color signal, and the stoppage of the flip-flop circuit.
It is also possible to cause the SECAM color signal processing circuit to perform a color killer operation. In particular, if the color killer operation is not performed reliably when receiving PAL color signals, the color TV screen will have abnormalities different from those on the transmitting side due to demodulating the PAL color signals with a completely different SECAM color processing circuit. Colors will appear, which is very inconvenient. Traditionally used
The SECAM color signal discrimination circuit detects the difference from the 4.43MHz carrier wave of the PAL color signal by extracting the discrimination signal of 4.25MHz, which is the carrier wave of the (B-Y) signal, and simply performing frequency discrimination. However,
4.43MHz and 4.25M for received signals in weak electric fields and out of tune
It becomes difficult to identify Hz, and as mentioned above, the color killer often malfunctions when receiving PAL color signals, and conversely, if you try to prevent malfunctions, the color killer sensitivity deteriorates, which is a disadvantage.

The signal discrimination circuit according to the present invention makes effective use of the fact that the discrimination signals of two different frequencies, 4.25 MHz and 4.40 MHz, are repeated for each line of the SECAM color signal, and the detection characteristics of the FM detection circuit are shown in Fig. 2. By simply setting the detection output current with opposite polarity at two frequencies as shown in the figure, it is possible to obtain sufficiently high discrimination discrimination and color killer sensitivity without malfunctions in verification and color killer operations. Furthermore, it is possible to provide a SECAM color signal discrimination circuit suitable for integration into an integrated circuit.

Although one embodiment of the present invention has been described above, it is clear that the present invention is not limited to the above, and for example, the FM detection circuit may have another circuit configuration.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing an embodiment of the present invention.
FIG. 3 is a diagram explaining the operation of an FM detection circuit, FIG. 3 is a diagram explaining the operation of an embodiment of the present invention, and FIG. 4 is a circuit diagram explaining a specific circuit of an embodiment of the present invention. . 1...FM detection circuit, 2...Discrimination signal input terminal,
3... Gate pulse input terminal, 4... Phase shift circuit,
5, 6, 7, 8, 9, 10, 13, 14, 15,
16, 30, 31...Transistor, 25...Color signal amplification stage, 27...Flip-flop.

Claims (1)

[Claims] 1. In a color television signal receiving circuit in which two color discrimination signals are transmitted line-sequentially as a carrier wave with a different frequency for each scanning line, an FM that performs frequency discrimination on the two color discrimination signals and extracts them as a differential output current. a detection circuit, one of the first output currents of the differential output currents is supplied to the commonly coupled emitters of the first transistor and the second transistor, and the other second output current is supplied to the third transistor and the fourth transistor. to the common coupled emitters of the transistors of the first
A control signal that is inverted for each scan line is applied between the common coupling bases of the transistor and the fourth transistor and the common coupling bases of the second transistor and the third transistor. A third output current from the common coupled collectors of the third transistor and the third output current is connected to the second transistor and the fourth transistor.
A signal comprising: a transistor differential switch circuit for extracting a fourth output current from the commonly coupled collectors of the transistors; and means for extracting the difference between the third output current and the fourth output current as a discrimination output current. Discrimination circuit.