JPH04247790A - Receiving circuit - Google Patents

Abstract

PURPOSE:To obtain always table picture quality without being affected by a tracking error in the receiving circuit. CONSTITUTION:When a band characteristic between receiving channels are in dispersion due to a tracking error and a level of a color burst signal extracted from a composite video signal by a burst separation circuit 21 is fluctuated, a control voltage fed to a cathode of a tuning varactor diode 24 of an intermediate frequency tuning circuit 8 from an ACC circuit 22 is changed and a tuning frequency of the intermediate frequency tuning circuit 8 is corrected to eliminate the dispersion in the band characteristic.

Description

[Detailed description of the invention]

0010

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving circuit used in television receivers, video tape recorders, etc.

[0020]

2. Description of the Related Art Conventionally, the receiving circuit of a television receiver, for example, is composed of a tuner (tuning) section (1) and an audio/video signal processing section (2), as shown in FIG. The high frequency signal received by the antenna is first input to the input tuning circuit (3) of the tuner section (1), from which a predetermined channel is selected, and then amplified by the high frequency amplifier circuit (4) and then sent to the input tuning circuit (3). After the interfering signal is removed by the interstage tuning circuit (5), the signal is supplied to the mixing circuit (6). This mixing circuit (6) mixes it with the local oscillation signal given from the local oscillation circuit (7) and converts the frequency into an intermediate frequency signal, and the next intermediate frequency tuning circuit (8) removes the excess signal component. Only the intermediate frequency signal is extracted and guided to the next stage audio/video signal processing section (2). The intermediate frequency signal derived to this audio/video signal processing section (2) is
After excess signal components are removed by the SAW filter (9), the signal is amplified by the next video intermediate frequency amplification circuit (10).
From this video intermediate frequency amplification circuit (10) to the audio detection circuit (
The 4.5 MHZ audio intermediate frequency signal taken out through 11) is amplified by the audio intermediate frequency amplifier circuit (12), then detected by the FM detection circuit (13), and taken out as an audio signal. The signal is output to a speaker via a frequency (audio) amplification circuit and the like. Also,
The video intermediate frequency signal taken out from the video intermediate frequency amplification circuit (10) is detected by the video detection circuit (14) and taken out as a composite video signal, which is then led to the next video amplification circuit (15). There is. At that time, an automatic frequency adjustment (hereinafter referred to as "AFT") circuit (16) converts the deviation of the video intermediate frequency obtained from the video intermediate frequency amplification circuit (10) into a DC voltage, and the local oscillation circuit (7) ( In this case, it is applied as a control voltage to the voltage controlled oscillation circuit (voltage controlled oscillation circuit) to correct the deviation in the oscillation frequency. Also,
Automatic gain control (hereinafter referred to as "AGC") circuit (17)
A video intermediate frequency amplification circuit (10) and a high frequency amplification circuit (4) are installed so that the signal output level from the video amplification circuit (15) is constant regardless of the signal input level from the receiving antenna.
The gain is controlled.

[0030]

[Problem to be Solved by the Invention] However, in a receiver circuit having such a configuration, a variable capacitance diode whose capacitance changes when the tuning voltage (reversely applied voltage to the cathode side) is varied is used to tune each circuit. Because it uses an electronic tuning method,
Tracking errors (deviations in band characteristics) due to variations in components such as capacitors and diodes used for tuning.
This error tends to cause variations in the band characteristics of the receiving channels among the channels and fluctuations in image quality between the channels. In other words, the band characteristics of the tuning circuit section have a large effect on image quality, and if the band characteristics are such that the level of the color subcarrier is low relative to the video carrier, the coloring of the image will be soft; If the band characteristics are such that the level of the color subcarrier becomes high, the image will not be colored hard, and there is a risk that beats will occur due to the color subcarrier and the audio carrier. This is a problem especially in high-definition television receivers and video tape recorders, and with the recent promotion of CATV, regulations regarding various types of adjacent channel interference have become stricter, and the tuning frequency with respect to the tuning voltage has become stricter. When it becomes necessary to speed up the change in the tracking error and to increase the selectivity of the tuning circuit section, the influence of this tracking error increases. The present invention has been made in view of these points, and it eliminates variations in band characteristics between each channel due to tracking errors, and always maintains stable image quality between each channel regardless of tracking errors. It is an object of the present invention to provide a receiving circuit that can be obtained.

[0040]

[Means for Solving the Problems] In order to achieve the above object, the present invention selects a predetermined channel from among the received high frequency signals, converts the frequency into an intermediate frequency signal in a mixing circuit, and then performs intermediate frequency tuning. In a receiving circuit that extracts audio and a composite video signal from an intermediate frequency signal extracted from the circuit, the tuning frequency of the intermediate frequency tuning circuit is corrected according to the level of the color burst signal extracted from the composite video signal. A correction means is provided. Specifically, the correction means includes a burst separation circuit that extracts a color burst signal from a composite video signal, and a tuning correction voltage that corresponds to the level of the color burst signal from this burst separation circuit. The correction circuit includes a correction circuit that generates
An automatic color saturation control (hereinafter referred to as "ACC") circuit that keeps the level of the carrier color signal extracted from the composite video signal constant is used, and the control voltage from the ACC circuit is used as the tuning correction voltage to control the intermediate frequency tuning circuit. The voltage is applied to the cathode side of the tuning variable capacitance diode.

[0050]

[Operation] According to such a configuration, when the band characteristics between each receiving channel vary due to tracking error and the level of the color burst signal extracted from the composite video signal by the burst separation circuit fluctuates, Accordingly, the control voltage applied as a tuning correction voltage from the ACC circuit to the cathode side of the tuning variable capacitance diode of the intermediate frequency tuning circuit changes. As a result, the tuning variable capacitance diode
The capacitance of the lead changes, and the tuning frequency of the intermediate frequency tuning circuit is corrected.

[0060]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. It should be noted that the same parts as those in the prior art will be given the same reference numerals and the explanation thereof will be omitted. In this embodiment, if the band characteristics of the received channels vary between channels due to tracking error, the level of the color subcarrier with respect to the video carrier wave will vary, and if the level of the color subcarrier with respect to the video carrier wave becomes high. As the level of the color burst signal increases and the level of the various subcarriers decreases with respect to the video carrier, the color burst signal level decreases. Therefore, as shown in Fig. 1, an intermediate frequency tuning circuit (
8) is corrected according to the level of the color burst signal extracted from the composite video signal. Specifically, a sync separation circuit (18) extracts a horizontal sync signal from a composite video signal output from a video amplification circuit (15), and a sync separation circuit (18) extracts a horizontal sync signal from a composite video signal output from a video amplification circuit (15). Waveform shaping circuit (19) that generates a gate pulse (generally uses a slightly delayed horizontal synchronization signal) for extracting a burst signal.
, a band amplification circuit (20) for extracting and amplifying a color burst signal and a carrier color signal from the composite video signal output from the video amplification circuit (15);
A burst separation circuit (21) extracts a color burst signal from the output of the waveform shaping circuit (19) based on a gate pulse from the waveform shaping circuit (19), and a color burst signal extracted by this burst separation circuit (21). - ACC circuit (22
). And this ACC circuit (2
The control voltage from 2) is applied to the band amplifier circuit (20) to adjust its gain so that the level of the carrier color signal is constant, and is also applied to the intermediate frequency tuning circuit (8) to adjust the color for the video carrier wave. The tuning frequency is corrected so that the level of the subcarrier becomes constant (that is, so as to eliminate variations in band characteristics). For example, the control voltage from the ACC circuit (22) is applied to the tuning variable capacitance diode (24) connected in parallel with the tuning coil (23) constituting the intermediate frequency tuning circuit (8), as shown in FIG. ) through a bias resistor (25). Here, (26), (27), and (28) are tuning capacitors.

Therefore, according to such a configuration, when the band characteristics of the receiving channels vary among channels due to tracking error, and the level of the color subcarrier with respect to the video carrier varies, the burst separation circuit ( Since the level of the color burst signal extracted by 21) varies between channels, the intermediate frequency tuning circuit (8) is changed from the ACC circuit (22).
The control voltage applied as a tuning correction voltage to the cathode side of the tuning variable capacitance diode (24) also changes. As a result, the capacitance of the tuning variable capacitance diode (24) changes, and the tuning frequency of the intermediate frequency tuning circuit (8) is corrected so as to eliminate level fluctuations of the color subcarrier with respect to the video carrier. That is, when the level of the color subcarrier with respect to the video carrier becomes low, the intermediate frequency tuning circuit (8
) is corrected so that the tuning frequency of the intermediate frequency tuning circuit (8) becomes lower, and conversely, when the level of the color subcarrier with respect to the video carrier wave becomes high, the tuning frequency of the intermediate frequency tuning circuit (8) is corrected to become higher. become. In this embodiment, the tuning variable capacitance diode of the intermediate frequency tuning circuit is connected in parallel with the tuning coil, but the invention is not limited to this, and the tuning variable capacitance diode may be connected in series.

[0080]

As described above, according to the receiving circuit of the present invention, the tuning frequency of the intermediate frequency tuning circuit is corrected according to the level of the color burst signal extracted from the composite video signal, thereby improving the tracking performance. This eliminates variations in the band characteristics of the received channels between channels due to errors, that is, variations in the level of the color subcarrier relative to the video carrier, so the image quality is always stable without being affected by tracking errors. can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a circuit configuration of the present invention.

FIG. 2 is a diagram showing a specific circuit configuration example of the intermediate frequency tuning circuit.

FIG. 3 is a diagram showing an example of a conventional circuit configuration.

[Explanation of symbols]

1 Tuner section 2 Audio/video signal processing section 8 Intermediate frequency tuning circuit 21 Burst separation circuit 22 ACC circuit 24 Variable capacitance diode for tuning

Claims (3)

[Claims] [Claim 1] A predetermined channel is selected from among the received high-frequency signals, frequency-converted into an intermediate-frequency signal by a mixing circuit, and then audio and a composite video signal are extracted from the intermediate-frequency signal taken out by an intermediate-frequency tuning circuit. 1. A receiving circuit comprising: a correcting means for correcting the tuning frequency of said intermediate frequency tuning circuit in accordance with the level of a color burst signal extracted from said composite video signal. 2. The correction means includes a burst separation circuit for extracting a color burst signal from a composite video signal, and a tuning correction according to the level of the color burst signal from the burst separation circuit. 2. The receiving circuit according to claim 1, further comprising a correction circuit that generates a voltage. 3. As the correction circuit, an automatic color saturation control circuit that maintains a constant level of the carrier color signal extracted from the composite video signal is used, and the control voltage from the automatic color saturation control circuit is adjusted to a tuning correction voltage. 3. The receiving circuit according to claim 2, wherein the voltage is applied to the cathode side of a tuning variable capacitance diode of said intermediate frequency tuning circuit.