Patent ID: 7277135

Claim:
An apparatus including video signal control circuitry for use in a video display system in which a variation in a brightness level of a video display signal causes a corresponding variation in a beam current signal, said video signal control circuitry comprising: a control electrode to convey said beam current signal; control circuitry coupled to said control electrode and responsive to said beam current signal and a brightness control signal by providing a gain control signal, wherein said gain control signal has a nominal value determined substantially by said brightness control signal and is variable about said nominal value in substantial relation to said beam current signal, and wherein said control circuitry includes lowpass filter circuitry coupled to said control electrode, and current source circuitry coupled to said lowpass filter circuitry and responsive to said brightness control signal by shunting a current via said lowpass filter circuitry; and amplifier circuitry coupled to said control circuitry and responsive to said gain control signal and an input video signal by providing said video display signal, wherein a ratio of said video display signal and said input video signal has a value determined substantially by said gain control signal; wherein a substantially constant average video display signal brightness level is maintained notwithstanding a variation in a brightness level of said input video signal.