CATHODE CLAMPING CIRCUIT APPARATUS WITH DIGITAL CONTROL

摘要

A cathode clamping circuit apparatus with digital control comprises: a variable voltage source for generating the bright voltage and cathode clamping circuits for producing dc component voltages for color component signals respectively. Each of the cathode clamping circuits has: a capacitor for coupling one of color component signals to an output terminal; the shunt regulator for generating the sub-bright voltage in accordance a current signal, the bright and the sub-bright voltages being summed to produce the dc component voltages by connecting the variable voltage source to the shunt regulator in series; the variable current source for producing the current signal in accordance with a voltage signal; a d/a converter responsive to a control signal for producing the voltage signal; a transistor for clamping the color component signal with the sum voltage of the bright voltage and sub-bright voltages in response to the clamp pulse produced from the color component signals R, G. and B and the vertical and horizontal synchronizing pulse accompanied with the color component signals. Removal of variable resistors eliminates poor contact therein and contributes automatization of the cathode clamping circuit.