| 摘要 |
PURPOSE:To obtain a circuit setting a DC level stably, by comparing the fluctuation of a reference signal level such as a black signal with a preset permissible value, and shifting the DC level of an original signal through the D/A conversion of a count value of the counter either incremented or decremented depending on the result of the comparison. CONSTITUTION:A video signal Vin outputted from an image sensor is applied to a DC amplifier 10. An output VA of a DC amplifier 10 is compared with a reference set value Vref at a comparator 40, and if the output is greater than the set value, a signal is applied to a down or up input of an up-down-counter 50 from a gate 70 and if smaller, from a gate 80. An output of the counter 50 is converted into an analog signal at a D/A converter 60 and supplied as a level shift input VSF of the DC amplifier to compensate the fluctuation of the reference level of the video signal input Vin. |
