JPS6244755B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention aims to provide a demodulation device that can obtain good images.

FIG. 1 shows a block diagram of a demodulator for a color television receiver. In Figure 1, 1 is an R-Y demodulation circuit, 3 is a B-Y demodulation circuit, 2 is a G-Y matrix circuit, 4, 5, and 6 are color difference signal emitter follower circuits, and 8 is a circuit that adds R-Y and Y. , an output circuit for amplifying, 9 an output circuit for adding and amplifying G-Y and Y, 10 an output circuit for adding and amplifying B-Y and Y, 7 an emitter follower circuit that supplies the Y signal to the color output circuits 8 to 10. It is. 11a,
11b is a carrier color signal input terminal to which input signals of opposite polarity are applied. 12a, 12b, 13
A and 13b are subcarrier signal input terminals for demodulation, and the polarities of the signals at a and b are opposite. 1
4, 15, and 16 are output terminals connected to a cathode ray tube. 17 is a luminance signal input terminal.

Next, its specific configuration will be explained using FIG. 2.

Carrying color signals applied to the bases of transistors 18 and 19 and transistors 20, 21, 22, 2
Phase detection is performed by the subcarrier signal applied to the bases of transistors 20 and 22, and the (RY) signal is applied to the collectors of transistors 20 and 22.
A -(RY) signal appears at the collector of 23.
This (RY) signal is applied to the output circuit 8 via the emitter follower circuit 4, added to the luminance signal Y, and the primary color signal R is outputted to the output terminal 14.

Also, a carrier color signal applied to the bases of transistors 24 and 25 and transistors 26, 27, 2
Phase detection is performed by the subcarrier signal applied to the bases of transistors 27 and 29.
A (B-Y) signal appears at the collector of transistor 9, and a -(B-Y) signal appears at the collectors of transistors 26 and 28. The (B-Y) signal is applied to the output circuit 10 via the emitter follower circuit 6, and is added to the Y signal to output the primary color signal B at the output terminal. -(RY)
The signal and the -(B-Y) signal are applied via resistors 30 and 31, and become the (G-Y) signal, which is applied to the emitter follower circuit 5, where it is added to the Y signal in the output circuit 9, and sent to the output terminal 15. Outputs G primary color signal.

The emitters of transistors 18 and 19 are resistors 3
2 and 33, and the connection point thereof is grounded through a series circuit of a transistor 34 and a resistor 35. A constant voltage is applied to the base of the transistor 34 from resistors 36, 37 and a diode 38, and a constant current I is applied to the transistor 34.
is starting to flow. The emitters of transistors 24 and 25 are also coupled by resistors 39 and 40, and this coupling point is grounded through a series circuit of transistor 41 and resistor 42. The above-mentioned constant voltage is also applied to the base of this transistor 41, so that a constant current I flows through the transistor 41. A series circuit of a transistor 43 and a resistor 44 is connected to the connection point between the resistors 30 and 31.
The same constant voltage is also applied to this transistor 43, and the value of the resistor 44 is made twice the value of the resistors 42 and 35 so that a constant current of 1/2I flows through the transistor 43. Collectors of transistors 20 and 22, collectors of transistors 21 and 23,
Values R _O of load resistors 45, 46, 47, 48, and 49 connected between the connection point between the collectors of transistors 26 and 28, the collectors of transistors 27 and 29, and the resistors 31 and 31 and the DC power supply Vcc.
are all equal. The emitters of transistors 20 and 21 are directly connected to the collector of transistor 18, the emitters of transistors 22 and 23 are directly connected to the collector of transistor 19, the emitters of transistors 26 and 27 are directly connected to the collector of transistor 24, and the emitters of transistor 28 are directly connected to the collector of transistor 24. and 29 are directly connected to the collector of transistor 25, respectively.

From the above configuration, emitter follower circuits 4, 5, 6
The DC level at the base of is expressed by the following formula,
In reality it is set to 7.7 volts.

The operating range of the Vcc-1/2IR _O Y signal is from 7.7 volts to the V _BE of transistors 50 and 51 (base-emitter voltage approx.
The voltage after subtracting 0.7 volts is 7.7 - 2 x 0.7 = 6.3 (volts) or less. Circuits 5 and 6 have the same configuration as circuit 4, and circuits 9 and 10 have the same configuration as circuit 8.

Output circuits 8, 9, and 10 have a gain of 40 times. In general, the product of gain and band is constant, so if the gain is as high as 40 times as described above, the frequency characteristics will be poor, the resolution will drop, and the image quality will deteriorate. Therefore, in order to improve the resolution, it is sufficient to lower the gains of the output circuits 8, 9, and 10, but it is necessary to increase the gains of the signals that enter the output circuits 8, 9, and 10 instead. A gain can be easily applied to the Y signal, and a change in the DC level caused by increasing the gain can be absorbed by the brightness volume. Although the gain can be easily increased for color difference signals, there are the following drawbacks.
That is, when the demodulation gain is increased by increasing the resistance values of resistors 45, 46, 47, 48, and 49, the DC level of the color difference signal decreases based on the above formula, and as a result, the dynamic range of the Y signal circuit decreases. If the value is narrowed, a saturation phenomenon will occur near white. Furthermore, if the values of the resistors 32, 33, 39, and 40 are reduced to increase the gain of the color difference signal, the input dynamic range of the carrier color signal becomes narrower, causing a saturation phenomenon in blue, etc., where the carrier color signal level is high. become.

The present invention aims to eliminate the above-mentioned drawbacks, and one embodiment of the present invention will be described below with reference to the drawings. FIG. 2 shows one embodiment of the present invention, and the same parts as in FIGS. 1 and 2 are given the same numbers and the description thereof will be omitted. The features of this circuit are the R-Y demodulation circuit 1a, the B-Y demodulation circuit 3a,
Load resistance 45 in the G-Y matrix circuit 2a,
The values of 46, 47, 48, and 49 are increased to increase the gain of the output signal. In order to compensate for a drop in the DC level at the output terminal, a constant current is caused to flow from the power supply to the output terminal. Specifically, the DC power supply Vcc, the collectors of transistors 20 and 22, the collectors of transistors 21 and 23,
Transistors 52, 53,
54, 55, and 56 are connected, and a DC voltage obtained in a series circuit of a diode 57, a transistor 58, and a resistor 59 is applied to the bases of these transistors 52-56. The base of transistor 58 is connected to the anode of diode 38.

Since the operation of each circuit of transistors 52, 53, 54, 55, and 56 is the same, transistor 5
2. The operations of the resistor 45 and transistor 20 will be explained. When the value R _o of resistor 45 is increased to R ₁ , the amplitude of the (RY) signal obtained at the collector of transistor 20 increases. However,
The DC level at the collector of transistor 20 decreases. In other words, as shown in the above equation, transistor 2
The DC level E of the collector of 0 is as follows when the value of the resistor 45 is R _O and the transistor 52 is not present.

E=Vcc-1/2 If the _IRO transistor 52 is added and the value of the resistor 45 is increased to R ₁ =R _O +ΔR, the DC level E becomes as follows. Note that the constant current flowing through the transistor 52 is I _O .

E=Vcc-(1/2I-I _O )R ₁ =Vcc-(1/2I-I _O )(R _O +△R) =Vcc-1/2IR _O -1/2I△R+I _O (R _O + △R) Therefore, if the relationship between IO, △R, and I is determined to satisfy the condition -1/2I△ _R +I _O (R _O +△R)=0, the DC level of the collector of the transistor 20 will be There is no need to change. In this way, the gain of the color difference signal output can be increased without changing the DC level of the demodulation circuit.

Basically, the carrier color signal and the subcarrier signal may be input in reverse order, and the signal is applied to the base of at least one transistor of the differential amplifier in the circuit, and a fixed bias is applied to the base of the other transistor. You may also add it. Furthermore, the color difference signal output obtained from the differential amplifier can be taken out from either transistor, and it is possible to change the circuit taking these things into consideration.

As described above, according to the present invention, the gain of the color difference signal can be increased without changing the DC level of the demodulation circuit, so the gain of the output circuit in the next stage can be reduced accordingly, and the frequency characteristics can be improved. Since the image quality can be improved, a good image can be obtained.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional demodulator, and Figure 2 is a block diagram of a conventional demodulator.
FIG. 3 is a circuit diagram of the demodulator, and FIG. 3 is a circuit diagram of the demodulator according to an embodiment of the present invention. 1a, 3a... Demodulation circuit, 2a... Matrix circuit, 45, 46, 47, 48, 49... Load resistance, 52, 53, 54, 55, 56... Transistor, 20, 21, 22, 23, 26 ,27,
28, 29, 58, 34, 43, 41... Transistor, 38, 57... Diode, 30, 31
……resistance.

Claims (1)

[Claims] 1. The emitters of a pair of transistors are coupled together, another transistor is inserted between this coupling point and the ground, and a constant current flows through the other transistor in a direct current manner. applying one of the carrier color signal and the subcarrier signal to the base of the transistor, applying the other of the carrier color signal and the subcarrier signal to the base of at least one of the pair of transistors, and applying the other of the carrier color signal and the subcarrier signal to the base of at least one of the pair of transistors; A load resistor is connected between the collector of the transistor and the DC power supply, and a constant current circuit is provided to supply a constant current from the DC power supply to the collector of one of the transistors, and the demodulated output of the color difference signal is taken out from the collector of the one transistor. A demodulation device characterized in that the demodulation gain of the color difference signal is increased without changing the DC level of the demodulation output. 2. Connect the emitters of a pair of transistors, insert another transistor between this connection point and ground, configure the other transistor to have a constant current flowing through it, and connect the carrier color signal to the base of the other transistor. and one of the subcarrier signals, and the other of the carrier color signal and the subcarrier signal is applied to the base of at least one of the pair of transistors, and between the collector of at least one of the pair of transistors and the DC power supply. A demodulation circuit is constructed by connecting a load resistor to the transistor, providing a constant current circuit to supply a constant current from a DC power source to the collector of one of the transistors, and extracting the demodulated output of the color difference signal from the collector of the one transistor. , is equipped with two demodulation circuits configured in this way, the outputs of both demodulation circuits are coupled via a resistor, a load resistance is connected between this coupling point and a DC power supply, and this load resistance also has a DC constant. A constant current circuit is provided between the above connection point and the ground so that current flows, and a constant current circuit is also provided between the above connection point and the DC power source to flow a constant current into the above connection point, and another color difference signal is generated from the above connection point. A demodulation device characterized in that the demodulation gain of each color difference signal is increased without changing the DC level of each demodulation output by extracting the demodulation output.