A circuit used to control the level of a video signal should have a 3-dB cutoff frequency of greater than 5 MHz for a television application or 100 MHz for a monitor application. CMOS-based digital potentiometers typically cannot be used as video devices because their frequency responses barely exceed 1 MHz. For such applications, a good choice would be a variable-gain amplifier (VGA) with analog or digital gain control. VGAs are offered as standard, off-the-shelf components by various component manufacturers However, as the frequency range of VGAs improves, other parameters degrade. For instance, it's difficult to design high-frequency devices with low dc offsets and tight gain characteristics. In video applications, spreads in the gain and high dc offsets require additional effort to regenerate the black level or white balancing.
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