JPH0547023B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention relates to a video and audio intermediate frequency integrated circuit (hereinafter referred to as VIF) used in, for example, a television receiver.
(referred to as SIF/IC), and is particularly concerned with the suppression of both video and audio signals.

[Conventional technology]

Conventionally, there has been a device of this type as shown in FIG. In the figure, 1 is a monolithic IC called VIF/SIF/IC, and in the IC 1,
10 and 11 are a VIF amplifier and an AM detector (video intermediate frequency processing circuit) that amplify and detect the video intermediate frequency signal output from the tuner 30, 12 is an AGC amplifier, and 13 is a tuner AGC control voltage volume 33.
tuner AGC control voltage determined by
A tuner AGC circuit that controls the tuner 30 according to the output of the AGC amplifier 12; 14 is a limiter amplifier that controls the output of the SIF filter external to the IC 1;
15 is an FM detector (audio intermediate frequency processing circuit) which performs FM detection on the output of the limiter amplifier 14 and outputs an audio signal. Note that 20 to 29 are terminals of the ICI, 20 is an input terminal of the tuner 30 output, and 21
is a terminal for outputting the video signal from the AM detector 11 to the outside of the IC1, 22 is an input terminal to the limiter amplifier, 23 is a feedback terminal, and 24 and 25 are external terminals.
Terminal for installing FM detection coil 37, 26
2 is an audio signal output terminal, 27 is a tuner AGC control terminal (reference voltage terminal), 28 is a tuner AGC output terminal, and 29 is a terminal for attaching an AGC filter.

Further, 34 is an SIF filter for extracting an audio intermediate frequency signal from the video signal from IC1, 35 is an audio suppression switch, 36 is a capacitor, 37 is an FM detection coil, 38 is a capacitor for FM detection, 33 is a tuner AGC control voltage volume, 31 is a video suppression switch, and 32 is an AGC filter capacitor.

Next, the operation will be explained.

The video intermediate frequency signal of the receiving station outputted from the tuner 30 is intermediate frequency amplified by the VIF amplifier 10 in the IC1, and detected by the AM detector 11 to become a video signal, which is output to the outside of the IC1. This video signal is processed by the video signal processing circuit in the subsequent stage and output as a video, and is also processed by the SIF filter 3.
4 extracts the audio intermediate frequency signal component, and the audio intermediate frequency signal is detected by the FM detector 15 via the limiter amplifier 14 inside the IC 1,
An audio signal is output from the terminal 26. The output of the AM detector 11 is amplified by the AGC amplifier 12 and applied to the VIF amplifier 10 to control its gain, and is also applied to one of the inputs of the tuner AGC amplifier 13. The gain of the tuner 30 is controlled according to the output and the terminal 27 voltage determined by the tuner AGC control voltage volume 33.

[Problem that the invention seeks to solve]

The conventional VIF/SIF/IC is configured as described above, and the video signal is suppressed by applying a voltage to the terminal 29 from the outside or by grounding the terminal 29 so that the gain of the VIF amplifier is minimized. Furthermore, the audio signal was suppressed by connecting the feedback terminal 23 of the limiter amplifier to the ground in a direct current manner.

Therefore, when attempting to suppress video and audio simultaneously, it was necessary to simultaneously control separate suppression circuits as described above outside the IC.

This invention was made to solve the above-mentioned problems with conventional devices, and provides a VIF/SIF/IC that can suppress both video and audio signals simultaneously by changing one terminal voltage. It is intended to.

[Means for solving problems]

The VIF, SIF, and IC according to this invention are
The voltage at the reference voltage terminal of the AGC circuit is
a comparator for determining that the AGC circuit is outside the normal operating range; a first switch for grounding one of the inputs of the tuner automatic gain control circuit by the output of the comparator; A video/audio muting means comprising a second switch that grounds one of the inputs of a limiter amplifier that controls the output of the frequency filter is provided.

[Effect]

In this invention, the video/audio muting means detects that the voltage applied to the reference voltage terminal is outside the normal operating range of the tuner AGC circuit and suppresses the output of the video/audio intermediate frequency processing circuit. By setting the voltage at one existing terminal of an integrated circuit to a voltage outside the normal operating range, video and audio can be simultaneously suppressed without increasing the number of terminals.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a VIF/VIF according to an embodiment of the invention.
This figure shows an SIF/IC, and in the figure, the same symbols as in FIG. 2 indicate the same things.

This embodiment is different from the one in FIG. 2 in that a video/audio suppression switch 40 is provided between the tuner AGC control terminal 27 of IC 1 and the ground, a video suppression switch (first switch) 41, an audio suppression switch (first switch) A switch (2) 42 is provided inside the IC 1 and connects the voltage of the terminal 27 and the reference voltage source 4.
4 voltage and turns on both switches 41 and 42, and the audio suppression switch 35 outside the ICI shown in FIG. 2 is eliminated.

This comparator 43 and reference voltage source 4
4, video suppression switch 41, audio suppression switch 4
2 constitutes a video/audio muting means 50 that suppresses the output of the video and audio intermediate frequency processing circuit when a voltage outside the normal operating range of the AGC circuit 13 is applied to the reference voltage terminal 27 of the tuner AGC circuit 13. There is.

Figure 3 also shows the input level of the VIF amplifier.
The relationship between the AGC filter voltage and the tuner AGC output is shown, and FIG. 4 is a diagram showing the relationship between the tuner AGC control voltage and the tuner AGC delay point.

Next, the operation will be explained. As shown in Figure 3, when the tuner AGC control voltage is varied,
The tuner AGC output voltage changes accordingly.
The VIF amplifier input level, that is, the tuner AGC delay point changes. However, as shown in FIG. 4, even if the tuner AGC control voltage is varied, there is a dead region in which the tuner AGC delay point does not change below a certain voltage.

Therefore, in this embodiment, a reference voltage is provided in this dead area, and when the comparator 43 detects that the tuner AGC control voltage has fallen below this voltage,
Switches 41 and 42 inside the IC lower the AGC filter voltage to ground, and also lower the feedback terminal 23 of limiter amplifier 14 to ground, thereby simultaneously suppressing video and audio. In addition,
In this embodiment, the video suppression switch 31 external to IC1
It is also possible to suppress only the video by turning on.

Note that in the above embodiment, only the video can be suppressed independently using the video suppression switch outside the ICI, but by using the conventional suppression method in combination, the video,
It is also possible to suppress each voice independently.

〔Effect of the invention〕

As described above, according to the VIF/SIF/IC according to the present invention, there is a comparator that determines that the voltage at the reference voltage terminal of the tuner AGC circuit is outside the normal operating range of the tuner AGC circuit, and an output of this comparator. a first switch that grounds one of the inputs of the tuner automatic gain control circuit; and a second switch that grounds one of the inputs of the limiter amplifier that controls the output of the audio intermediate frequency filter by the output of the comparator. A video/audio muting means is provided to simultaneously suppress the outputs of the video and audio intermediate frequency processing circuits when a voltage outside the normal operating range of the AGC circuit is applied to the reference voltage terminal of the tuner AGC circuit. Therefore, by simply changing the voltage at one existing terminal of the integrated circuit to a voltage outside the normal operating range, it is possible to simultaneously suppress video and audio without increasing the number of terminals.

[Brief explanation of the drawing]

FIG. 1 shows VIF, SIF, and
IC circuit diagram, Figure 2 is the conventional VIF/SIF/IC circuit diagram, Figure 3 is AGC filter voltage and tuner
A diagram showing the relationship with AGC output, Figure 4 is tuner
FIG. 3 is a diagram showing the relationship between AGC control voltage and tuner AGC delay point. In the figure, 1 is a monolithic IC (VIF).
SIF/IC) 10 and 11 are VIF amplifiers, AM detectors (video intermediate frequency processing circuits), 12 are AGC amplifiers,
13 is tuner AGC circuit, 34 is SIF filter,
14 is a limiter amplifier, 15 is an FM detector (audio intermediate frequency processing circuit), 30 is a tuner, 33 is a tuner AGC control voltage volume, 27 is a reference voltage terminal, 40 is a video and audio suppression switch, 41 is a video suppression switch, 42 is a 43 is a comparator, 44 is a reference voltage source, and 50 is video/audio muting means.

Claims (1)

[Claims] 1. A video intermediate frequency processing circuit that amplifies and detects a video intermediate frequency signal output from a tuner external to the integrated circuit and outputs a video signal; and an audio intermediate frequency processing circuit that detects an audio intermediate frequency signal obtained through an audio intermediate frequency filter and outputs an audio signal; and a tuner automatic gain control that controls the gain of the tuner according to the output of the video intermediate frequency processing circuit. a comparator for determining that a voltage at a reference voltage terminal of the automatic tuner gain control circuit is outside the normal operating range of the automatic tuner gain control circuit; and a second switch that grounds one of the inputs of the limiter amplifier that controls the output of the audio intermediate frequency filter according to the output of the comparator. A video/audio intermediate frequency integrated circuit featuring: