AUTOMATIC AMPLITUDE CONTROL CIRCUIT

摘要

PURPOSE:To obtain the automatic amplitude control circuit whose transient response speed is sufficiently high at application of power or at start of reception and having a sufficiently stable characteristic from which no flicker noise or the like is generated at signal demodulation by varying a coefficient of a comparator circuit. CONSTITUTION:An input signal level detection circuit 6 latches a frame pulse with a latch 61 to obtain a high level video signal with a MUSE signal converted into a digital signal at an A/D converter circuit 5, a 2nd line frame pulse is latched by a latch 62 to obtain a low level video signal, its output difference is extracted by a subtractor 63 to obtain a detection signal of an input signal level. A nonlinear comparator circuit 7 obtains a difference between the input level detection signal outputted from the signal level detection circuit 6 and a reference value (object value) from a subtractor 72, and the nonlinear processing circuit implements nonlinear processing. The output signal is inputted to an integration circuit 8, and an adder 81 adds the signal having been outputted from the integration circuit 8 and the signal outputted from the nonlinear comparator circuit 7.