| 摘要 |
PURPOSE:To enable automatic stable gain control of high performance free from malfunction to an erroneous signal, by generating a reference pulse of constant width by using the leading edge of a synchronizing signal separate output. CONSTITUTION:When a synchronizing signal contracts and a separating circuit operates at the front-poach leading edge of a composite video signal and back-poach trailing edge to output pulse (b'), monostable multivibrator 16 is triggered by the leading-edge rise of pulse (b') appearing at synchronizing-signal separating circuit 15 to generate pulse (C'), so that reference pulse generating circuit 19 will output referefence pulse (C') of time-T pulse width, constant amplitude and a constant base-line level synchronizing with the leading edge of the front poach. The input composite video signal is passed through variable gain circuit 11 and clamping circuit 13 generates signal (d') having the top of the synchronizing signal clamped at voltage VCL. Then, signal (d') and pulse (c') are added together to obtain output (e') and peak holding circuit 17 detects peak voltage VC3. When circuit 11 is balanced by voltage VC1 of circuit 17, voltage VC3 is lower than VC1 and the gain increases to balance the automatic gain controller, so that the output will be constant. |
