| 摘要 |
The test pattern generator of synchronous signal processing circuit generates test pattern when no composite video signal is received so that noise from self resonant synchronous signal is not displayed. The circuit includes a synchronous signal extractor (2') for extracting vertical/horizontal synchronous signal from composite video signal, an automatic frequency controller (3') for comparing frequency of horizontal synchronous signal with sawtooth wave, a horizontal oscillator (6') for controlling frequency of sawtooth wave according to the compared result, a ramp generator (9') for generating ramp signal, a vertical synchronous signal generator (V) for generating vertical synchronous signal according to the ramp signal and a test pattern generator (T) for generating test pattern when no composite video signal is received.
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