| 摘要 |
PURPOSE:To correct accurately a DC transmission rate by comparing an average picture level and a pedestal level so as to superimpose the pedestal pulse having an amplitude in response to the result of comparison onto a video signal. CONSTITUTION:The video signal Y clamping the pedestal to a reference voltage EP is inputted to an input terminal 4. An APL (an average picture level) detection section 1 averages the signal by a time constant comprising resistance R11, R12 and a capacitor C and the APL is detected. A comparator circuit 7 comprising transistors (TRs) Q15, Q16 is operated only at a pedestal section and the reference level EP and the APL are compared at said section. The result of comparison is obtained as a pulse current (i) proportional to the APL, which flows via a current mirror load comprising a diode D and a TRQ17. The current (i) flows superimposing a resistance R13 which flows an input video signal and the video signal where a transmission rate correcting signal is superimposed at the pedestal part is obtained from the output of a TRQ18. |
