Influence of Non-ideal Integration on Sampling Circuits with Internal Antialiasing Filtering

Ideally, filtering properties of a sampling circuit (SC) with internal antialiasing filtering are completely determined by its weight function. Imperfect parameters of the SC units may significantly distort its transfer function. Insufficient gain and input resistance of an operational amplifier (opamp) used in the SC integrator are among the major factors that may adversely affect antialiasing filtering. Influence of these factors on the SC transfer function is examined in this paper. To this end, equations for the transfer functions of SCs with finite gain and input resistance of the opamps are derived. It is shown that these factors have minimal impact on the amplitude-frequency responses (AFRs) of the SCs within their passbands. At the same time, they significantly influence the SCs´ phase-frequency responses (PFRs) within the pass-bands and the SCs´ AFRs within the stopbands.