JPS5811094Y2 - television receiver - Google Patents

Description

[Detailed explanation of the idea] This invention relates to a television receiver.

FIG. 1 shows a video output circuit including a video detection circuit of a conventional television receiver.

In FIG. 1, a video detection circuit 1 is connected to a power source having a voltage VCC1, and a video output transistor Q1 amplifies the output of the video detection circuit 1.

One end of the resistor R1 is connected to a power source having a voltage vCC2, and the other end is connected to the collector of the video output transistor Q1, thereby serving as a load for the video output circuit.

Resistor R2 is an emitter resistance of video output transistor Q1.

Further, a series circuit of a capacitor C1 and a resistor R3 is inserted between the emitter of the video output transistor Q1 and ground.

The collector of the video output transistor Q1 is directly connected to the cathode electrode K of the cathode wiring 2.

Note that the circuit shown in FIG. 1 omits a frequency characteristic compensation circuit such as a collector peaking circuit or an emitter peaking circuit of the video output transistor Q1, for example.

Next, the operation of the circuit shown in FIG. 1 will be briefly explained.

The base of the transistor Q0 is directly connected to the video detection circuit 1, and therefore the base bias of the video output transistor Q1 is provided by the video detection circuit 1.

Under this base bias, the video output transistor Q
A certain DC bias is applied to the emitter of the image output transistor Q1 by the resistor R2, and to the collector of the image output transistor Q1 by the resistor R1.

Image output transistor Q directly connected to image detection circuit 1
At the base of 1, a so-called composite video signal waveform as shown in FIG. 2 appears, and the video output transistor Q1
As shown in FIG. 3, a signal whose phase is inverted and amplified from the waveform shown in FIG. 2 appears at the collector of FIG.

Since the cathode electrode of the cathode ray tube 2 is directly connected to the collector of the video output transistor Ql, an image is reproduced on the cathode ray tube 2 with a signal waveform as shown in FIG.

In this case, the brightness can be controlled by changing the DC level of the collector of the video output transistor Q1 by changing the resistor R2, and the so-called contrast control can be performed by changing the AC line and gain by changing the resistor R3. It is possible.

Now, consider a case where the average video level of the video signal applied to the base of the video output transistor Q1 changes.

FIG. 2a shows an example of a signal with a small average video level, and the average level of the video signal is level LAI, and FIG. 2a shows a signal with an intermediate average video level, and the average level of the video signal is level LCI.

The signal shown in Fig. 2 a or b is output from the video output transistor Q.
The waveform at the collector when added to the base of 1 is:
As shown in FIG. 3a or b, respectively, the average levels LA□ and Lc2 (both are potentials relative to the earth level LE) of the video signal change depending on the DC gain and AC gain of the video output stage.

For example, if the AC gain and DC gain are equal, the difference in the average level of the video on the base side of the video output transistor Q1 will be inverted and amplified as it is on the collector side.
The white level Lw and black level LB of both are the same level.

On the other hand, if the DC gain is zero (see Figure 1, a DC cut capacitor is inserted between the video detection circuit 1 and the base electrode of the video output transistor Q1, and another suitable capacitor is inserted at the base of the video output transistor Q1. (in the case where a fixed bias is applied), the average level of the collector of the video output transistor Q1 becomes a constant potential, so that the average level of both images LA2 . LC2 becomes the same level.

In the case of the circuit shown in FIG.
and the parallel circuit impedance of resistor R3), the DC gain becomes smaller than the AC gain, resulting in the above-mentioned 2
This is an intermediate behavior for the seed example.

Now, the DC transmission rate is defined by the following equation.

That is, if W is the DC transmission rate, U is the amount of black level variation, and V is the amount of average video level variation, then the following is true.

According to this, when the AC gain = DC gain in the previous example, the black level does not change, so the black level fluctuation amount is O and the DC transmission rate is 100%, and when the DC gain is zero, the black level fluctuation amount U- The average video level fluctuation amount is W, and the DC transmission rate is O.

Generally, when the DC transmission rate is low, the fidelity of the luminance signal for image reproduction on the cathode ray tube 2 deteriorates.

Various methods have been devised to increase this DC transmission rate (
In addition to DC transmission, a method called DC regeneration is also used.)
However, the current situation is that it has a complicated rotational configuration.

Therefore, an object of this invention is to provide a television receiver that can increase the DC transmission rate with a simple configuration and improve the fidelity of image reproduction.

An embodiment of this invention is shown in FIG.

That is, in this television receiver, a resistor R4 is inserted and connected between a resistor R1 connected to the collector of the video output transistor Q1 and a power supply having a voltage vCC1,
In addition, a capacitor C2 is connected between the connection point of the resistor R4 and the resistor R1 and the ground, and the other configuration is the first one.
It is the same as the television receiver shown in the figure.

Next, the operation will be explained in comparison with the operation of the television receiver shown in FIG.

In the case of the television receiver of FIG. 1, the voltage of the bias power supply of the collector of the video output transistor Q1 is vCC2, and in the case of the television receiver of FIG. 4, the bias power supply of the collector of the video output transistor Q□ is the voltage vCC
2, but the bias voltage is the capacitor C
This is the voltage across 2.

Furthermore, in the case of the television receiver shown in FIG. 1, when the average video level of the signal is high, the white level at the collector of the video output transistor Q1, that is, the cathode electrode K of the cathode ray tube becomes high (relative to ground). This means that the own level (as well as the black level and other gradations) that should be correctly reproduced (potentially) varies, but in the case of the television receiver shown in Figure 4, signals with a high average video level are Since the average value Ic of the signal current is large, the voltage across the capacitor C2 (Vcc2- (Ic
X (represented by The difference from the white level when the level is small is smaller than in the case of the television receiver of FIG. 1.

As a result, the DC transmission rate can be increased with a simple configuration of adding the resistor R4 and the capacitor C2, and the fidelity of the image reproduced on the cathode ray tube 2 can be improved.

As described above, the television receiver of this invention can increase the DC transmission rate with a simple configuration, and as a result, can improve the fidelity of images reproduced on the cathode ray tube.

[Brief explanation of the drawings] Figure 1 is a configuration diagram of the main parts of a conventional television receiver;
3 and 3 are explanatory diagrams of its operation, and FIG. 4 is a diagram showing the main part of an embodiment of this invention. 1...Video detection circuit, 2...Cathode ray tube, Ql...Video output transistor, R1, R2
, R3, R4...Resistance, C1, C2...
・Container.

Claims (1)

[Scope of utility model registration request] a video detection circuit, a video output transistor to which the output of the video detection circuit is applied to the base, a load resistor with one end connected to the collector of the video output transistor, and a cathode line whose cathode is connected to the collector of the video output transistor. a resistor whose one end is connected to the other end of the load resistor; a capacitor whose one end is connected to the connection point of the resistor and the load resistor and whose other end is grounded; and a capacitor connected to the other end of the resistor. A television receiver equipped with a DC power supply.