JPS6222306B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a television receiver using an integrated circuit, and its purpose is to reproduce a stable and faithful screen without being affected by variations in the DC potential of the integrated circuit. do.

The first step was to achieve more faithful screen reproduction than before.
As shown in the figure, there is a so-called DC reproduction type television receiver in which the demodulator 1, video amplification circuit 2, and cathode of the cathode ray tube 3 are coupled in a DC manner to faithfully reproduce the average brightness of the screen. be.
In addition, by integrating these circuits, the number of parts used has been reduced, the size has been reduced, and the performance has been improved.

A conventional example of such a television receiver is shown in the second example.
As shown in the figure. In the figure, 7 is an integrated circuit, which includes a video intermediate frequency amplification circuit 14, a demodulator 1 that demodulates the video intermediate frequency signal 15 amplified by this circuit 14, a preamplifier circuit 5 that amplifies the video signal, and an emitter follower. The transistor 6 of the configuration is integrated. Reference numeral 11 denotes a transistor for amplifying the output signal of the integrated circuit 7 to drive the cathode 4 of the cathode ray tube 3, and these transistors are coupled in a DC manner for DC reproduction as described above.

Furthermore, as is well known, in an integrated circuit, integrating a capacitor inside increases the chip area of the integrated circuit, which is also disadvantageous in terms of cost. Therefore, each amplifier circuit 14, 5, transistor 6, and demodulator 1 inside the integrated circuit 7 are coupled in a direct current manner.

Therefore, the integrated circuit 7 constructed in this manner also operates as a kind of DC amplifier, and has a very large degree of DC amplification from the input terminal P to the output terminal Q, and each amplifier circuit 14 , 5, etc. are amplified in each part, and appear as large variations in DC potential at the output terminal Q. This variation in DC potential is directly amplified by the transistor 11 and appears on the cathode 4 of the cathode ray tube 3. Therefore, the average brightness of the screen reproduced on the cathode ray tube 3 varies, and depending on the television receiver, some images are bright and others are dark. It had the disadvantage that things could occur.

For example, if we consider a case where the potential at the output terminal Q of the integrated circuit 7 varies widely, and if the current amplification factor h _FE of the transistor 11 is sufficiently large, the collector current I _C11 of the transistor 11 will be I _C11 ≒ (V _Q - V _BE11 )/R ₁₂ where, V _Q : Potential of output terminal Q, V _BE11 : Base of transistor 11.
The forward voltage drop between the emitters is _R12 : the resistance value of the resistor 12, and _IC11 increases in proportion to the potential of the output terminal Q.

As a result, the voltage drop across the resistor 13 also increases, lowering the collector potential of the transistor 11, that is, the potential of the cathode 4 of the cathode ray tube 3, and as a result, the cathode bias of the cathode ray tube 3 becomes shallower and the brightness increases. On the other hand, when the potential at the output terminal Q of the integrated circuit 7 is low and fluctuates, the brightness decreases.

In this way, the average luminance changes due to variations in the integrated circuit 7.

In order to eliminate such drawbacks, conventionally, as shown in FIG. 2, a variable resistor 9 is used to vary the voltage V _CC supplied to the integrated circuit 7, absorbing variations in the DC potential at the output terminal Q, and increasing the voltage at the cathode. I have tried to apply a constant DC potential to 4.

Here, the capacitor 10 is a bypass capacitor for the video signal component, and is inserted to prevent the variable resistor 9 from becoming a load resistance of the integrated circuit 7 due to the video signal component flowing through the variable resistor 9. .

However, such a conventional method has the drawback that it is necessary to adjust the variable resistor 9 according to variations in the output of the integrated circuit 7 and variations in the power supply V _CC supplied to the integrated circuit 7 .

Also, when the ambient temperature changes, transistor 1
The forward voltage between the base and emitter of 1 changes,
Therefore, the collector potential of the transistor 11, that is, the DC potential of the cathode 4 of the cathode ray tube 3 changes, and even if the ambient temperature changes, the average brightness of the screen also changes.

In contrast, the present invention can eliminate the above-mentioned conventional drawbacks and provide a television receiver having an image amplification circuit that is stable against component variations and changes in ambient temperature.

FIG. 3 shows an embodiment of the present invention. In the figure, elements having the same functions as the elements in FIG. 2 will be described with the same reference numerals.

3 differs from FIG. 2 in that except for the variable resistor 9 and the bypass capacitor 10, the transistor 100, resistors 101, 103, 104,
The transistor 10 using a capacitor 102
The emitter of the transistor 0 is connected to the power supply V _CC through a resistor 103, its base is directly connected to the collector of the transistor 6, and the collector is connected to the emitter of the transistor 11 through a resistor 104. Further, a resistor 101 and a capacitor 102 are each inserted between the base of the transistor 100 and the power supply V _CC .

In the above configuration, the emitter potential of the transistor 6, that is, the potential of the output terminal Q, is determined by the internal circuit of the integrated circuit 7 and the power supply V _CC as described above. Here, transistors 6 and 11
Assuming that the current amplification factor h _FE is sufficiently high, the emitter current I _E and collector current I _C of transistor 6 are
is I _E ≒ I _C ≒ V _Q /R _8where , V _Q : potential of output terminal Q, R ₈ : resistance value of emitter resistor 8, and the emitter and collector currents are
is proportional to the potential of

Therefore, due to variations in the integrated circuit 7, the output terminal Q
As the potential increases, I _E ≈I _C increases proportionally, and the voltage drop across resistor 101 increases. Then, the base bias of transistor 100 becomes deeper, and the collector current I _C ' of transistor 100 increases. This collector current I _C ' flows into the resistor 12 through the resistor 104, increasing the voltage drop across the resistor 12, that is, raising the emitter potential of the transistor 11, the potential at point R in FIG. Voltage decreases. On the other hand, transistor 1
Since the base potential of transistor 1 is the same potential as the potential of the output terminal Q of the integrated circuit 7, it increases as the potential of the output terminal Q increases, so the bias of the transistor 11 is caused by the increase in the potential of the output terminal Q. It maintains the bias state as before, and works to compensate the collector current of the transistor 11 at a constant level. As a result, the increase in voltage drop across the resistor 13 is suppressed, and the collector potential, that is, the cathode 4 of the cathode ray tube 3 is reduced.
The potential of the cathode is kept constant, the cathode bias is kept constant, and the brightness is kept constant.

As described above, according to the configuration shown in FIG. 3, the transistor 100 functions to correct the potential variations at the output terminal Q of the integrated circuit 7, thereby always maintaining optimum brightness.

Furthermore, if the ambient temperature changes, for example increases, the forward voltage drop between the bases and emitters of transistors 11 and 100 decreases.

Further, the potential at the output terminal Q of the integrated circuit 7 is generally designed to be constant regardless of changes in ambient temperature in order to provide versatility. Therefore, the collector current I _C11 of the transistor 11 works to increase, but on the other hand, the collector current I _C ' of the transistor 100 also increases, which raises the emitter potential of the transistor 11 and decreases the collector current of the transistor 11 for the above-mentioned reason. Therefore, the brightness remains constant in this case as well.

As described above, the configuration shown in FIG. 3 also has the effect of suppressing changes in brightness due to changes in ambient temperature due to the function of the transistor 100.

Here, the capacitor 102 is for bypassing the video signal component current to the resistor 101, and
This is to operate so that 01 acts only on potential variations at the output terminal Q of the integrated circuit 7.

Further, the resistor 103 is used to set the collector current I _C ' of the transistor 100.

As explained above, according to the present invention, not only can variations in the potential at the output terminal Q of an integrated circuit be corrected without adjustment, that is, without increasing the number of adjustment steps, but also it is possible to compensate for variations in the potential at the output terminal Q of an integrated circuit. It can be operated stably, and its effects are great in practical terms.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the configuration of a television receiver using a DC reproduction method, FIG. 2 is a circuit diagram of a conventional television receiver using an integrated circuit, and FIG. 3 is a diagram of a television receiver according to an embodiment of the present invention. FIG. 2 is a circuit diagram of a digital receiver. DESCRIPTION OF SYMBOLS 1... Demodulator, 3... Braun tube, 4... Cathode, 5... Preamplifier circuit, 6, 11... Amplifying transistor, 7... Integrated circuit, 100... Transistor, 101... Resistor.

Claims (1)

[Claims] 1 a first video amplification transistor with an emitter follower configuration integrated circuit;
a second video amplification transistor whose collector is directly connected to the emitter of the video amplification transistor and whose collector is directly connected to the cathode of the cathode ray tube; a resistor and a capacitor inserted in parallel between the collector of the first video amplification transistor and the power supply; and a transistor whose emitter is connected to the power supply via a resistor, whose base is directly connected to the collector of the first video amplification transistor, and whose collector is connected to the emitter of the second video amplification transistor. Jiyoung receiver.