CLAMP CIRCUIT

摘要

PURPOSE:To eliminate not only a dispersal signal but also a low frequency noise by selecting a time constant of a differentiating circuit so as to be suitable for eliminating the low frequency noise and compensating the deterioration in the elimination ratio of an energy spread signal with an energy spread signal elimination signal. CONSTITUTION:The time constant represented by a capacitance of a capacitor 31 and a resistance of a resistor 32 is set to a value sufficiently eliminating low frequency noise. Moreover, an elimination signal generating circuit 33 outputs a residual energy spread signal elimination signal having a level characteristic inverse to that of an energy spread signal resident in an output of a clamp circuit synchronously with a frame pulse supplied to a terminal 34. The eliminating signal is amplified up to a prescribed signal amplitude by an amplifier 35 and fed to a switch 20 closed at the reception of a MUSE signal via a switch 36 and added to a difference signal between a reference DC level and a detection output of a DC level for clamp level period of the output signal of a D/A converter 19 and fed to a differentiating circuit, in which the level is clamped so that the mean DC level of a horizontal synchronizing signal is made coincident with the level of the summing signal.