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 R_{IN} = (4 x 10_{12}) / (f x Gain)

For Gains = 80 ... 128, use R_{IN} = (8 x 10_{12}) / (f x Gain)

For Gains = 160 ... 256, use R_{IN} = (16 x 10_{12}) / (f x Gain)