| 摘要 |
<p>PURPOSE:To accurately correct a gain by providing a gain set value selecting circuit, selecting a gain set value according to the pulse width and frequency of a pilot signal, and outputting it. CONSTITUTION:The pilot signal for AGC (automatic gain control) which is implanted during a gain correction period in synchronism with an AGC timing signal is converted into a video signal through a variable attenuator 1 and then converted into a logarithmic value by a logarithmic converting circuit 2. A subtracting circuit 3 subtracts the level set value, selected according to the sent pulse width and frequency, from the converted logarithmic value. The output of the circuit 3 is added by an adding circuit 6 to a last gain set value and the sum value is the attenuation quantity (gain correction quantity) of an attenuator 1. This controlled variable is held by a holding circuit 7 until a next AGC timing signal is inputted. Thus, the accurate gain correction is made.</p> |
