JPH045309B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention includes a video intermediate frequency amplifier, a video detection circuit, an intercarrier audio intermediate frequency detector, and an automatic local oscillation frequency controller, and is applicable to a television receiver configured by an integrated circuit. related to the signal processing circuit of the machine.

FIG. 1 is a schematic block diagram of a signal processing circuit of a conventional television receiver. In the configuration, the video intermediate frequency amplifier 1 includes a tuner (not shown).
A video intermediate frequency signal is applied from the input terminals 2 and 3 through input terminals 2 and 3. After amplifying the video intermediate frequency signal, the video intermediate frequency amplifier 1 transmits it to the video detection circuit 4.
give to The video detection circuit 4 detects the video intermediate frequency signal and outputs the video detection output from the terminal 5. At the same time, the video detection circuit 4 extracts a carrier signal from the video intermediate frequency signal and supplies it to the automatic local oscillation frequency controller 8. The video detection circuit 4 includes a balanced output circuit, the automatic local oscillation frequency controller has a balanced input circuit, and the video detection circuit 4 and the automatic local oscillation frequency controller 8 are connected in a balanced manner.

On the other hand, the video intermediate frequency signal is applied from the other output of the video intermediate frequency amplifier 1 to the intercarrier audio intermediate frequency detector 6, and the intercarrier intermediate frequency signal is output from the terminal 7. Such a signal processing circuit is provided within a single semiconductor substrate and is constituted by a bipolar monolithic semiconductor integrated circuit, and has conventionally been frequently used in television receivers.

In such a signal processing circuit, when the gains of the video intermediate frequency amplifier 1, the video detection circuit 4, the intercarrier audio intermediate frequency detector 6, and the automatic local oscillation frequency controller 8 are increased, for example, the gain of the video detection circuit 4 increases. Feedback occurs from the terminal 5 to the input terminals 2 and 3 of the video intermediate frequency amplifier 1 due to stray capacitance, electromagnetic induction, etc., and as the gain of the video intermediate frequency amplifier 1 is increased, it becomes unstable and causes oscillation and mutual interference. It becomes easier. This phenomenon also applies to the intercarrier audio intermediate frequency detector 6 and the automatic local oscillation frequency controller 8. In particular, when the video intermediate frequency amplifier 1, the video detection circuit 4, the intercarrier audio intermediate frequency detector 6, and the automatic local oscillation frequency controller 8 are integrated into ICs, oscillation occurs due to the feedback of AC components through wiring, resistance, or inductance within the IC. and mutual interference are more likely to occur.

Therefore, the main object of the present invention is to provide a signal processing circuit for a television receiver that can operate stably even when the gain is increased by inputting the circuit currents of each block in a balanced manner, especially in an alternating current manner. be.

To summarize this invention, a video intermediate frequency amplifier, a video detection circuit, and an automatic local oscillation frequency controller are connected in series via differential amplifier circuits each configured to be balanced in terms of alternating current. The intermediate frequency amplifier and the intercarrier audio intermediate frequency detector are also connected in series through a differential amplifier circuit configured to have balanced AC input to form a signal processing circuit.

The above objects and other objects and features of the present invention will become more apparent from the detailed description given below with reference to the drawings.

FIG. 2 is a schematic block diagram of one embodiment of the present invention. This FIG. 2 is the same as FIG. 1 except for the following points. That is, the video intermediate frequency amplifier 1
0 includes a balanced output circuit, and the video detection circuit includes a balanced input circuit. And a video intermediate frequency amplifier 10
and the video detection circuit 11 are connected in a balanced manner. Similarly, the intercarrier audio intermediate frequency detector 12 includes a balanced input circuit, and the video intermediate frequency amplifier 10 includes a balanced input circuit.
and intercarrier audio intermediate frequency detector 12 are connected in a balanced manner. In this way, the video intermediate frequency amplifier 10, the video detection circuit 11, and the automatic local oscillation frequency controller 8 are connected in a balanced manner, and the video intermediate frequency amplifier 10
By connecting the intercarrier audio intermediate frequency detector 12 and the intercarrier audio intermediate frequency detector 12 in a balanced manner, stable operation can be achieved. That is, when the respective gains of the video intermediate frequency amplifier 10, the video detection circuit 11, the automatic local oscillation frequency controller 8, and the intercarrier audio intermediate frequency detector 12 are increased, for example, video detection is detected from the output terminal 5 of the video detection circuit 11. Even if feedback occurs at the input section of the circuit 11 due to stray capacitance, electromagnetic induction, etc., the feedback component is added as an in-phase component because the input is a balanced input. Therefore, the loop gain does not become as large as in the signal processing circuit shown in FIG. 1, and oscillations are less likely to occur. Further, since the intercarrier audio intermediate frequency detector 12 and the automatic local oscillation frequency controller 8 are also connected in a balanced manner, the gain can be stably increased in the same manner as described above.

FIG. 3 is a specific electrical circuit diagram of a balanced output circuit and a balanced input circuit included in the video intermediate frequency amplifier 10 and the video detection circuit 11. In the figure, the video intermediate frequency amplifier 10 is a video intermediate frequency amplification circuit 101.
including. This video intermediate frequency amplification circuit 101 is composed of, for example, a differential amplification circuit, and outputs an output signal as a balanced output. This balanced output is provided to transistors 102 and 103. Transistors 102 and 103 constitute a differential amplifier circuit, and output terminals 109 and 1 are connected from their respective emitters to output terminals 109 and 103.
An output signal is provided to 10.

Output terminal 109,1 of video intermediate frequency amplifier 10
The video intermediate frequency signal output from 10 is applied to input terminals 111 and 112 of video detection circuit 11. Video intermediate frequency signals input to input terminals 111 and 112 are connected to capacitors 113 and 115, respectively.
It is input to the bases of transistors 114 and 116 via. The transistors 114 and 116 constitute a balanced input circuit. A video intermediate frequency signal is then provided from each emitter to the detection circuit 117. This detection circuit 117 is constituted by a differential amplifier circuit.

Note that the intercarrier audio intermediate frequency detector 12 shown in FIG. 2 is also provided with a circuit similar to the balanced input circuit of the video detection circuit 11.

As described above, according to the present invention, in a signal processing circuit including a video intermediate frequency amplifier, a video detection circuit, an intercarrier audio intermediate frequency detector, and an automatic local oscillation frequency controller, the output of the video intermediate frequency amplifier and the video The input of the detection circuit, the output of the video detection circuit, the input of the automatic local oscillation frequency controller, the output of the video intermediate frequency amplifier, and the input of the intercarrier audio intermediate frequency detector are configured to be AC balanced, respectively. Since the connection is made through a differential amplifier circuit, even if feedback occurs due to stray capacitance or electromagnetic induction, the feedback component becomes the common mode component, so the loop gain can be reduced.
Gain can be stably increased without causing oscillation. In particular, when the signal processing circuit according to the present invention is implemented as an IC, it is balanced in terms of alternating current, so no alternating current flows through the power supply and ground wiring within the IC, and extremely stable operation can be achieved.

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram of a conventional signal processing circuit. FIG. 2 is a schematic block diagram of one embodiment of the present invention. FIG. 3 is a specific electrical circuit diagram of a balanced output circuit and a balanced input circuit built into the video intermediate frequency amplifier and video detection circuit shown in FIG. 2, respectively. In the figure, 8 is an automatic local oscillation frequency controller;
10 is a video intermediate frequency amplifier, 11 is a video detection circuit, 12 is an intercarrier audio intermediate frequency detector, and 102, 103, 114, and 116 are transistors.

Claims (1)

[Claims] 1. A bipolar monolithic semiconductor device in which at least a video intermediate frequency amplifier, a video detection circuit, an intercarrier audio intermediate frequency detector, and an automatic local oscillation frequency controller are provided on a single semiconductor substrate. In a signal processing circuit for a television receiver constituted by an integrated circuit, the video intermediate frequency amplifier and the video detection circuit each include a balanced output circuit, and the video detection circuit and the intercarrier audio intermediate frequency detector The automatic local oscillation frequency controller includes a balanced input circuit each composed of an AC balanced differential amplifier circuit, and connects the output of the video intermediate frequency amplifier and the input of the video detection circuit in an AC balanced manner. The output of the video detection circuit and the input of the automatic local oscillation frequency controller are connected in an alternating current balance, and the output of the video intermediate frequency amplifier and the input of the intercarrier audio intermediate frequency amplifier are connected in an alternating current balance. A signal processing circuit for a television receiver, characterized in that the signal processing circuit is connected to the television receiver.