| 摘要 |
PURPOSE: To encode without any carrier leakage by applying balanced modulation to a clamped color difference signal with a continuous wave signal and phase-inverting the output by 180 degrees with a prescribed period, and applying balanced modulation to the result with a continuous wave signal in order to detect the difference in DC components. CONSTITUTION:A color difference signal inputted from a terminal 1 is clamped by an automatic clamping circuit 2, whose output is balanced-modulated with a color subcarrier wave from a carrier wave generating circuit 6 by a balanced modulator BM3. The output of the BM3 is supplied to a terminal 9 as a color difference signal and to a phase inverting circuit 7 which phase-inverts by 180 degrees at every one horizontal scanning period by using a signal from a timing circuit 8. The signal phase- inverted in the circuit 7 is balanced-modulated with the color subcarrier wave from the circuit 6 by the BM4 and the output of the BM4 is impressed to a detecting circuit 5. The circuit 5, based on a signal from the circuit 8, detects the difference in DC components at every one horizontal scanning period in the horizontal blanking cycle of the color difference signal to control the DC level of the circuit 2. As a result, the color difference signal is always clamped at the optimum DC level without any carrier leakage and thus encoded.
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