The AD6600 has two identical input attenuators, Channel Aand Channel B. These dual inputs are typically used as diversitychannels but may also process two independent IF signals. Formaximum oversampling the device is used in single channel mode;in this case only one input channel is required. The attenuatorsteps are 0 dB, –12 dB and –24 dB. The attenuator settings arebased on the decisions of the RSSI stage (see Peak Detector/RSSI section). The outputs of the attenuators connect to ananalog multiplexer that selects either Channel A or B for subsequentprocessing (see Input Mode). The selected signal drivesa dual-gain amplifier set to either 12 dB or 18 dB; the selectedgain is also determined by the RSSI stage. Therefore, based onall possible combinations of attenuation and gain, the inputsignal receives –12 dB to +18 dB of voltage gain in 6 dB steps(Table I). Overall gain-matching is typically within 0.1 dB. Witha bandwidth of 1 GHz, the phase delay through the front-endranges from 0.2 degrees to 0.5 degrees, depending on inputfrequency. Additionally, the input impedance does not changewith attenuator settings so there is no AM-to-PM distortion.