Digital Automatic Level Control for ADC

caroline11

ABSTRACT
The severity of overloads in an analog-to-digital converter circuit (A/D) as the analog input signal exceeds the dynamic range of the A/D has long been a target for any designer to solve,, Not only the analog signal spectrum becomes infested with fast-rising clipping distortion but the harmonics generated by clipping the high frequencies can "fold back11 and aggrevate the aliasing problem upon digital-to-analog (D/A) conversion,. One obvious solution is to place an automatic gain control (AGC) circuit before the A/D but analog methods generally have failed since the AGC must be "transparent' no degradation to the A/D; and be "threshold"f i„e» inactive until the analog signal approaches overload level; not to mention the side effects of "breathing" or "signal pumping"* With the advent of high-performance digitally-controlled attenuators (DCA8s)s a digital signal processor (dsp) can be utilized to provide precise threshold, instantaneous attack and many programmable features that suffers no drawbacks or side effects of the analog design* Further enhancement techniques can also provide more sophistication such as adaptive control process9