Does input impedance of the MAX1464 change with different PGA gain settings? How?
A. Yes. The input impedance as a function of PGA setting can be calculated by the expressions below, where “f” is the ADC clock frequency, and “Gain” is the PGA gain. A partial list of input impedance vs. PGA setting for both differential and single-ended inputs is given in the Electrical Characteristics (EC) table on pages 2 to 7 of the MAX1464 data sheet. For Gains = 1 … 64, use RIN = (4 x 1012) / (f x Gain) For Gains = 80 … 128, use RIN = (8 x 1012) / (f x Gain) For Gains = 160 …
