Television – Image signal processing circuitry specific to television – Gray scale transformation
Reexamination Certificate
1999-08-30
2001-12-25
Hsia, Sherrie (Department: 2614)
Television
Image signal processing circuitry specific to television
Gray scale transformation
C348S735000, C348S733000
Reexamination Certificate
active
06333765
ABSTRACT:
TECHNICAL FIELD
This invention relates to television receivers and, more particularly, to a television receiver having, for example, an AGC (Automatic Gain Control) circuit to control the gain on a tuner and intermediate frequency amplifier circuit.
PRIOR ART
In a prior art of this kind shown in
FIG. 5
, a television receiver
1
has an AGC amplifier circuit
2
and RF (Radio Frequency)-AGC circuit
3
to control the gain on a tuner and video intermediate frequency amplifier circuit
6
in response to an electric field intensity given by an input signal (radio frequency signal) supplied through an input terminal
4
.
For example, in a process of adjusting the RF-AGC circuit
3
before shipment from a factory, monitored on an output terminal
8
is an output voltage of the RF-AGC circuit
3
with respect to an input signal having an electric field intensity A, as shown in FIG.
4
. Variable resistance Rx is adjusted such that the output voltage becomes B.
In the conventional television receiver
1
, however, there is difference on an individual television receiver basis in characteristics such as of a video intermediate frequency amplifier circuit
6
, video wave detection circuit
7
and not-shown SAW filter (comb filter). Thus, there has been a necessity to manually adjust the variable resistance R
x
one by one before shipment from the factory. This, however, results in a problem that adjustment requires increased labor and time and, if adjusted, an adjustment error is encountered due to adjuster's subjective point of view.
SUMMARY OF THE INVENTION
It is therefore a primary object of the present invention to provide a television receiver which can be easily and accurately adjusted in gain on the tuner.
A television receiver according to the present invention, comprises: a tuner for receiving an input signal having a predetermined electric field intensity; a waveform detection means for detecting an output waveform of the tuner and outputting a video signal; a creating means for creating gain control voltage on the tuner in response to a difference in level between the video signal and a reference voltage; and a change means for changing the reference voltage such that the gain control voltage becomes a desired voltage value.
If for example an input signal having a predetermined electric field intensity is supplied to the tuner, the tuner creates a video intermediate frequency signal and audio intermediate frequency signal based on the input signal. The detecting means detects an output of the tuner and outputs a composite video signal. The composite video signal is supplied as an output of the detection means to the creating means. Meanwhile, the creating means is given a reference voltage. The creating means creates a gain control voltage on the tuner depending upon a difference between the output of the detection means and the reference voltage. The change means detects a gain control voltage by the detection means and change the reference voltage depending upon a result of the detection. This brings the gain control voltage to a desired voltage value.
According to the present invention, the creating means creates a gain control voltage on the tuner depending upon a difference between the output of the detection means and the reference voltage as an output of the change means, thereby saving time and labor in adjustment and hence eliminating adjustment error.
The above described objects and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 5638140 (1997-06-01), Krishnamurthy
patent: 5638141 (1997-06-01), Bae
patent: 58-83481 (1983-05-01), None
patent: 5-304430 (1993-11-01), None
patent: 6-178228 (1994-06-01), None
Kajiya Munetoshi
Okada Hirofumi
Arent Fox Kintner & Plotkin & Kahn, PLLC
Hsia Sherrie
Sanyo Electric Co,. Ltd.
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