| 摘要 |
A video system, for example an X-ray examination apparatus, includes a variable gain video amplifier (20) whose gain is varied by a control circuit (40), which produces a control signal at a control input (23) of the amplifier. The value of the control signal is derived to the control circuit from the ratio of a reference value (Vref) to the amplitude of the amplified video signal (Vu). This amplitude is measured in a detector (30) which supplies an amplitude signal (Vd) as input for the control circuit. By combining this ratio with the already adjusted gain (K), stored in a memory (47), practically instant adaptation of the gain is possible when the amplitude (Vi) of the input signal changes.
|
