| 摘要 |
A clamping circuit is included in the video processing section of a television signal processor and is arranged to clamp the pedestal or black level of the video signal to a reference voltage manifesting the black tone output of the receiver. The clamping circuit includes capacitive means responsive to the video signal, a reference voltage source for generating the reference voltage, a current source for generating current for charging the capacitive means, and a unidirectional conducting device for coupling the reference voltage source and the current source to the capacitive means and poled to clamp the signal excursions of one relative polarity developed at the output of the capacitive means to the reference voltage. The reference voltage source is arranged to maintain the reference voltage substantially invariant in response to video signal variation. The current source is peak current limited to prevent the capacitive means from being charged in response to the peaks of noise pulses occurring in the video signal. In a preferred arrangement, means are also provided to prevent the capacitive means from being charged in response to the sync pulse superimposed on the pedestal level. |
