JPH0698277A - Agc device for television receiver - Google Patents

Abstract

PURPOSE:To secure the optimal start-up time each time a channel is switched by storing data corresponding to the start-up time point of the optimal RF.AGC of each channel. CONSTITUTION:An AGC part 8 generates an AGC voltage for applying an AGC operation start point which fulfills both an S/N and a cross modulation characteristic to each channel, and reads the data of the optimal start-up time point from an ROM 7 each time the channel is switched. Then, the data of the optimal start-up time point are impressed on the base of a transistor Q, and a voltage at a variable resistor R is changed according to the impressed voltage value, so that the start-up time point of the RF.AGC can be set for each channel.

Description

Detailed Description of the Invention

[0001]

[0001]

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an RF / AGC device for a television receiver.

[0003]

[0002]

[0004]

2. Description of the Related Art Conventionally, a device having a circuit shown in FIG. 1 is known as this type of device. In the figure, reference numeral 1 is a front end, 2 is a SAW filter, 3 is a video intermediate frequency amplification section, 4 is a video detection section, 5 is a video amplification section, 6 is a PLL synthesizer, 7 is a ROM, and is surrounded by a dotted line in the figure. A portion is an AGC (automatic cane control) unit 8 as an AGC circuit, which feeds back by an output of the video amplification unit 5 and is connected in series to a noise removal unit 80 and an AGC.
The detection section 81, the AGC amplification section 82, and the RF / AGC section 83 are fed back to the front end 1, and the output of the AGC amplification section 82 is fed back to the video intermediate frequency amplification section 3. There is. Reference numeral 9 is a central processor unit (hereinafter referred to as CPU).

[0005]

Next, the operation will be described. AGC section 8
Is a stage of the AGC amplifying section 82 which constitutes this, and sets a voltage that determines a rising time point by a variable resistor R shown in the figure. On the other hand, the tuning voltage from the PLL synthesizer 6 is supplied to perform the local oscillation control of the front end 1. The tuning voltage is supplied by PLL of the data corresponding to the channel (frequency) data stored in the ROM 7 for each channel according to the instruction of the CPU 9.
This is performed by reading the synthesizer 6 and setting the frequency division ratio of the programmable divider forming the PLL synthesizer 6 by the data corresponding to the channel data.

[0006]

[0004]

[0007]

The conventional AGC device is
With the above-described configuration, when the rising time of RF / AGC for any channel is set by the variable resistor R, the optimum voltage value for other channels is generated when the gain of the front end varies. However, there are drawbacks such that the rising time is delayed or advanced, and when it is late, the intermodulation characteristics are deteriorated, and when it is early, the S / N ratio of the video signal is deteriorated.

[0008]

That is, since the gain of the front end varies depending on the channel (reception frequency), if the gain of the front end when receiving an arbitrary channel becomes high, the voltage of the AGC input to the front end becomes higher than the normal voltage. Get lower. Therefore, the signal input level at the start of the RF / AGC operation with respect to the input signal level decreases and the S / N ratio decreases.

[0009]

On the contrary, when the gain becomes low when an arbitrary channel is received, the RF / AG for the input signal level is reduced.
The operation start point of C becomes high, and AG is activated at a high signal input level.
Since C is not applied, the cross modulation characteristic is deteriorated.

[0010]

Therefore, the present invention stores the data corresponding to the optimum RF / AGC rise time for each channel in the memory, and obtains the optimum rise time each time the channel is switched. Is intended to provide.

[0011]

[0008]

[0012]

SUMMARY OF THE INVENTION An AGC device for a television receiver of the present invention, which has been made to solve the above problems, is a television which controls a gain of a front end of the television receiver by an AGC voltage from an AGC circuit. In the AGC device of the John receiver, a memory for storing tuning data of each channel and data corresponding to an optimum rising time point of the AGC voltage from the AGC circuit corresponding to these channels, and a memory for storing the data from the memory at the time of channel switching. AGC control means for reading the data corresponding to the optimum rising time of the AGC voltage corresponding to the channel and controlling the output operation of the AGC circuit.

[0013]

[0009]

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. Here, in FIG. 2, reference numerals 1, 2, 3,
4, 5, 6, 8, 80, 81, 82, 83 and 9
Is the same part as the motion code in FIG. 1, and the mutual connection has the same structure. Reference numeral 7 denotes a ROM, which stores the data corresponding to the tuning voltage for each channel, which is the function of the conventional example, and also the RF / AGC for each channel.
It also stores the data corresponding to the optimum start time of.

[0015]

The data corresponding to the optimum rising time will now be described. First, the AGC section 8 as an AGC circuit controls the AGC voltage generated by itself by an external control signal. Then, the AGC unit 8 generates an AGC voltage for giving an AGC operation starting point that satisfies both the S / N ratio and the intermodulation characteristic for each channel. An external control signal for generating such an AGC voltage is meant. In the ROM 7, various data can be rewritten.

[0016]

Reference numeral 10 denotes a D / A converter, which receives a command corresponding to the optimum rise time of the RF / AGC by the ROM 7 for each channel, converts the digital signal value into an analog quantity, and converts the analog value. A quantity of voltage is applied to the base of the transistor Q shown.

[0017]

Next, the operation will be described. Video amplifier 5
Feedback from the output terminal of the noise canceller 80, A
It reaches the AGC amplifier 82 via the GC detector 81, and here, the bias voltage that determines the rising time of the RF / AGC unit which is the next stage is set by the variable resistor R. Between the variable resistor R and the power source B, the bias voltage in the variable resistor R changes according to the change in the impedance of the transistor Q.

[0018]

On the other hand, the above-mentioned RF / AG for each channel
Since the data corresponding to the optimum rise time of C is stored in the ROM 7, the ROM 7 reads the data of the optimum rise time of each channel by the instruction of the CPU 9 every time the television channel is switched, and the D / A converter 10 reads the data. Order.

[0019]

Next, in the D / A converter 10, the data at the optimum rising time becomes a voltage value converted into an analog amount and is applied to the base of the transistor Q, and according to the applied voltage value. To change the voltage at the variable resistor R,
It is possible to set the rising time of F / AGC.

[0020]

Therefore, in this embodiment, since the optimum AGC operation starting point is set for each channel, the AGC operation is started at the same input signal level even if the front end gain changes for each channel, and S Both the / N ratio and the cross modulation characteristic can be satisfied.

[0021]

[0016]

[0022]

As described above, according to the present invention,
The AG that should control the rising time of the AGC so that the optimum AGC can be applied at the front end.
Since the AGC voltage from the C circuit is controlled, even if the front-end gain varies from channel to channel, both the intermodulation characteristic and the S / N ratio characteristic can be obtained for each channel. It can be kept in a satisfactory state at all times, whereby a good quality television image can be obtained.

[0023]

Further, since the gain of the front end is changed by changing the data stored in the memory, the setting can be easily changed.

[Brief description of drawings]

FIG. 1 is a block diagram of a circuit for explaining a conventional AGC device.

FIG. 2 is a block diagram of a circuit illustrating an AGC device according to an embodiment of the present invention.

[Explanation of symbols]

 1 Front End 2 SAW Filter 3 Video Intermediate Frequency Amplifier 4 Video Detector 5 Video Amplifier 6 PLL Synthesizer 7 ROM 8 AGC 80 Noise Removal 81 AGC Amplifier 82 AGC Amplifier 83 RF / AGC 9 CPU 10 D / A converter

Claims (1)

[Claims] 1. A television receiver AGC device for controlling a gain of a front end in a television receiver by an AGC voltage from an AGC circuit, wherein tuning data of each channel and the AGC circuit corresponding to these channels. A memory for storing the data corresponding to the optimum rising time of the AGC voltage, and the data corresponding to the optimum rising time of the AGC voltage corresponding to each channel is read from the memory at the time of channel switching, and the output operation of the AGC circuit is performed. And an AGC control means for controlling the AGC device for a television receiver.