JPH0556363A - Receiver circuit - Google Patents

Abstract

PURPOSE:To obtain stable picture quality regardless of a tracking error by individually adjusting the harmonic wave of each tuning circuit in accordance with the level of a color burst signal. CONSTITUTION:Control voltage in accordance with the level of a color burst signal in a state that a carrier color signal is adjusted to a constant level is generated from a tuning correction voltage generation circuit 27 composed of a band amplifier circuit 20, a burst separation circuit 21 and an automatic saturation control (ACC) circuit 22. The control voltage from the tuning correction voltage generation circuit 27 is corrected in such a manner that a tuning voltage is introduced to tuning voltage multiplex circuits 23, 24 together with the control voltage from a control circuit 26, multiplexed with tuning voltage impressed on the cathode side of variable capacity diode composing an input tuning circuit 3 and a inter-stage tuning circuit 5 and then impressed on the input tuning circuit 3 and the step space tuning circuit 5 in order of the input tuning circuit 3 and the tuning circuit 5. Every tuning frequency is corrected so that the level of a color auxiliary carrier for a video carrier may be constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving circuit used in a television receiver, a video tape recorder or the like.

[0002]

2. Description of the Related Art Conventionally, for example, a receiving circuit of a television receiver is composed of a tuner section 1 and an audio / video signal processing section 2 as shown in FIG. The high frequency signal received by the receiving antenna is input to the input tuning circuit 3 of the tuner unit 1 and a predetermined channel is selected from the input tuning circuit 3. Then, the high frequency signal is amplified by the high frequency amplifier circuit 4 and an interfering signal is further generated by the interstage tuning circuit 5. After being removed, it is supplied to the mixing circuit 6.

The high frequency signal supplied to the mixing circuit 6 is mixed with the local oscillation signal supplied from the local oscillation circuit 7 to be converted into an intermediate frequency signal, and the intermediate frequency tuning circuit 8 further removes excess signal components. After that, it is guided to the audio / video signal processing circuit 2.

The intermediate frequency signal guided to the audio / video signal circuit 2 is amplified by the video intermediate frequency amplification circuit 10 after the excess signal component is removed by the SAW filter 9, and guided to the audio detection circuit 11 for detection. It The audio intermediate frequency signal detected by the audio detecting circuit 11 is amplified by the audio intermediate frequency amplifying circuit 12, and then detected by the FM detecting circuit 13 to be taken out as an audio signal. It is guided to the speaker through the signal amplification circuit.

The video intermediate frequency signal extracted from the video intermediate frequency amplification circuit 10 is detected by the video detection circuit 14 and then guided to the video amplification circuit 15 as a composite video signal to be amplified and not shown. Are guided to the display device via a synchronizing circuit, a video signal processing circuit and the like.

The automatic frequency adjustment (AFT) circuit 16
Then, the shift of the video intermediate frequency obtained from the video intermediate frequency amplifier circuit 10 is converted into a DC voltage and applied to the local oscillation circuit 7 as a control voltage to correct the shift of the oscillation frequency.

Further, an automatic gain control (AGC) circuit 17
The gains of the high frequency amplification circuit 4 and the video intermediate frequency amplification circuit 10 are controlled so that the signal output level from the video amplification circuit 15 becomes constant regardless of the signal input level from the receiving antenna.

[0008]

In the receiving circuit as shown in the above-mentioned conventional example, the voltage applied to the cathode side of the variable capacitance diode constituting each tuning circuit of the input tuning circuit, the interstage tuning circuit and the local oscillation circuit. By changing the tuning frequency of each tuning circuit at the same time, the electronic tuning system receives the signal of a predetermined channel. Therefore, the characteristics of the parts such as coils, capacitors, and variable capacitance diodes that compose each tuning circuit. Due to the above variations, the tuning frequencies of the tuning circuits are rarely the same.

Therefore, in the case of producing such a tuner, it is common to adjust the tuning frequency of each tuning circuit by adjusting the inductance of the coil. Since it is common to use a so-called air-core coil instead of a transformer, it is difficult to automate adjustment by machines etc. due to its structural and productivity problems, and it is unavoidable to rely on human manual work. If there is a tracking error due to variations in the characteristics of the parts, compromising adjustment is forced in order to obtain a certain band characteristic for all channels, which adversely affects productivity.

Further, the variable capacitance diode used in each tuning circuit in order to reduce the above tracking error,
It is common to use parts with small deviation within the assembly that have uniform capacitance and ratio of capacitance change to the reverse applied voltage applied to the cathode side, that is, paired parts, but tracking error occurs due to variations in capacitors etc. It is difficult to eliminate all of them, and when the adoption of CATV is promoted as in recent years and regulations on various types of interference such as adjacent channel interference become stricter, the tuning frequency changes faster with respect to the tuning voltage and the selectivity of the tuning circuit increases. In a wideband tuner with a high level, the effect of tracking error was large.

However, the band characteristic of the tuning circuit has a great influence on the image quality of the television receiver or VTR, and the tracking error causes the image quality variation between channels. With respect to the receiver circuit used in the recorder, how to suppress this problem by design is an issue.

The present invention has been made in view of the above problems, and improves productivity by eliminating the adjustment of the tuning coil in the production process, and obtains stable image quality regardless of tracking errors due to characteristic variations of parts. It is an object of the present invention to provide a receiving circuit adapted to the above.

[0013]

In order to solve the above problems, the present invention selects a predetermined channel from a received high frequency signal by an input tuning circuit and an interstage tuning circuit,
After frequency conversion to an intermediate frequency signal in the mixing circuit, and after tuning the tuning frequencies of the input tuning circuit and the interstage tuning circuit to a predetermined channel in the receiving circuit for extracting the audio and composite video signals from the intermediate frequency signal, A control circuit for individually variably adjusting the tuning frequencies of the input tuning circuit and the interstage tuning circuit according to the level of the color burst signal extracted from the composite video signal is provided.

The color burst signal comprises a color burst separation circuit for extracting a color burst signal from the composite video signal and an automatic color saturation control circuit for making the level of the carrier color signal extracted from the composite video signal constant. A tuning correction voltage generating circuit for generating a tuning correction voltage according to the level, and a control for individually variably adjusting the frequencies of the input tuning circuit and the interstage tuning circuit according to the tuning correction voltage extracted from the tuning correction voltage generating circuit. And a circuit.

[0015]

According to the above structure, when the band characteristic between the receiving channels varies due to the tracking error and the level of the color burst signal extracted from the composite video signal by the burst separation circuit fluctuates, the tuning correction from the tuning correction voltage generating circuit is performed. The voltage fluctuates, and the control circuit individually controls the input tuning circuit and the interstage tuning circuit according to the fluctuation of the tuning correction voltage, and individually corrects the tuning frequencies of both tuning circuits to the optimum values.

[0016]

FIG. 1 is a block diagram of an embodiment of the present invention. The parts corresponding to those of the conventional example shown in FIG.

According to the present invention, the level of the color burst signal increases when the level of the color subcarrier is higher than that of the image carrier, and the level of the color burst signal decreases when the level of the color subcarrier is lower than that of the image carrier, according to the band characteristic of the receiving channel. Focusing on the reduction, the tuning frequencies of the input tuning circuit and the interstage tuning circuit are separately corrected according to the level of the color burst signal extracted from the composite video signal.

In FIG. 1, 18 is a sync separation circuit for extracting a horizontal sync signal, 19 is a waveform shaping circuit for producing a gate pulse for extracting a color burst signal from the horizontal sync signal, 2
0 is a band amplification circuit that extracts and amplifies the color burst signal and carrier color signal from the composite video signal, 21 is a burst separation circuit that extracts the color burst signal, and 22 is automatic color saturation control (ACC) that keeps the level of the carrier color signal constant. ) Circuit, 27 is the band amplification circuit 20, burst separation circuit 2
1 is a tuning correction voltage generating circuit including 1 and an ACC circuit 22.

Reference numerals 23 and 24 are tuning voltages for individually controlling the tuning frequencies of the input tuning circuit 3 and the interstage tuning circuit 5 according to the control signal from the control circuit 26 and the tuning correction voltage from the tuning correction voltage generating circuit 27. The superposition circuit 25 is a PLL circuit that controls the oscillation frequency of the local oscillation circuit 7 based on the control signal from the control circuit 26.

Therefore, the television signal input from the antenna to the tuner section 1 passes through the input tuning circuit 3, the high frequency amplifier circuit 4, the interstage tuning circuit 5, the mixing circuit 6 and the intermediate frequency tuning circuit 8 and then the intermediate frequency of a predetermined channel. It is taken out as a signal and guided to the video signal processing unit 2.

In the video signal processing section 2, the SAW filter 9, the video intermediate frequency amplification circuit 10, the video detection circuit 14 and the video amplification circuit 15 perform predetermined signal processing to derive the detected composite video signal.

The composite video signal output from the video amplifier circuit 15 is guided to the sync separation circuit 18, which separates and outputs the horizontal sync signal to the waveform shaping circuit 19. The waveform shaping circuit 19 shapes the waveform of the horizontal synchronizing signal to form a gate pulse for extracting the color burst signal, and supplies this gate pulse to the burst separation circuit 21.

On the other hand, the composite video signal derived from the video amplification circuit 15 is guided to the band amplification circuit 20, and the band amplification circuit 20 extracts the color burst signal and the carrier color signal, and the burst separation circuit 21 of the next stage. Supply to. The burst separation circuit 21 extracts the color burst signal from the band amplification circuit 20 by the gate pulse from the waveform shaping circuit 19 and guides it to the ACC circuit 22.

In the ACC circuit 22, the burst separation circuit 21
The level of the color burst signal supplied from
A control voltage corresponding to the level is generated. A part of this control voltage is fed back to the band amplifier 20, and the gain of the band amplifier 20 is adjusted so that the level of the carrier color signal becomes constant.

Therefore, the tuning correction voltage generating circuit 27 including the band amplification circuit 20, the burst separation circuit 21, and the ACC circuit 22 controls the carrier color signal according to the level of the color burst signal in a state where the carrier color signal is adjusted to a constant level. Voltage is generated.

The above-mentioned control voltage derived from the tuning correction voltage generating circuit 27 is led to the tuning voltage superposing circuits 23 and 24 together with the control voltage from the control circuit 26, and the variable voltage constituting the input tuning circuit 3 and the interstage tuning circuit 5. The tuning voltage applied to the cathode side of the capacitance diode (not shown) is superimposed, and the tuning voltage applied to the input tuning circuit 3 and the interstage tuning circuit 5 is corrected in the order of the input tuning circuit 3 and the interstage tuning circuit 5. , The tuning frequency is corrected so that the level of the color subcarrier with respect to the image carrier becomes constant.

The PLL circuit 25 detects the frequency of the local oscillation signal from the local oscillation circuit 7 based on the control signal from the control circuit 26, and controls the voltage so that the local oscillation circuit 7 oscillates at a constant frequency.

[0028]

Since the present invention has the above-mentioned structure, the input tuning circuit and the stage are adjusted in accordance with the level of the color burst signal extracted from the composite video signal by the control circuit of the synchronizing frequency of the input tuning circuit and the interstage tuning circuit. Since it can be corrected in the order of the inter-tuning circuit, it is possible to always obtain a constant band characteristic in all channels without adjusting the coils forming the input tuning circuit and the inter-stage tuning circuit in the production process.
It is possible to always obtain a stable image quality without fluctuation of the level of the color subcarrier with respect to the video carrier.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional example.

[Explanation of symbols]

 3 input tuning circuit 5 inter-stage tuning circuit 6 mixing circuit 21 burst separation circuit 22 ACC circuit 23, 24 tuning voltage superposition circuit 26 control circuit 27 tuning correction voltage generation circuit

Claims (2)

[Claims] 1. A predetermined channel is selected from the received high-frequency signal by an input tuning circuit and an inter-stage tuning circuit, and the frequency is converted into an intermediate frequency signal by a mixing circuit, and then the audio and composite video signals are output from the intermediate frequency signal. After tuning the tuning frequency of the input tuning circuit and the interstage tuning circuit to a predetermined channel, the input tuning circuit and the interstage tuning circuit are extracted according to the level of the color burst signal extracted from the composite video signal. A receiving circuit comprising a control circuit for individually variably adjusting the tuning frequency of the tuning circuit. 2. A predetermined channel is selected from the received high frequency signal by an input tuning circuit and an interstage tuning circuit, frequency is converted to an intermediate frequency signal by a mixing circuit, and then the audio and composite video signals are output from the intermediate frequency signal. In the receiving circuit for extracting the color burst, the color burst separating circuit for extracting the color burst signal from the composite video signal and the automatic color saturation control circuit for making the level of the carrier color signal extracted from the composite video signal constant are provided. A tuning correction voltage generating circuit for generating a tuning correction voltage according to the signal level, and the frequencies of the input tuning circuit and the inter-stage tuning circuit are individually variably adjusted according to the tuning correction voltage extracted from the tuning correction voltage generating circuit. A receiving circuit, which is provided with a control circuit for controlling.