We investigate the effects of the photonic sampling pulse's temporal width and the photodetection bandwidth on the channel response of time-interleaved photonic analog-to-digital converters (TIPADCs). Each sampling channel is modeled as a linear analog channel with a sampler, where the channel response is derived and analyzed theoretically. The results show that the finite temporal width of photonic sampling pulse will limit the channel analog bandwidth and the minimum feasible bandwidth of photodetection is the half of single channel sampling rate. The inter-symbol interference (ISI) induced by the finite bandwidth of photodetection will cause periodic ripples on the channel frequency response. Neither the photonic sampling with finite temporal width nor the ISI induced by the finite bandwidth of photodetection will result in excess noise. Experimental measurements on the channel responses of a TIPADC under different temporal widths and photodetection bandwidths verify the theoretical results.

We propose a photonic scheme to digitize RF signals with a programmable equivalent analog prefilter, where the filter impulse response is directly proportional to the time-reversed temporal shape of the sampling pulse and hence can be adjusted by shaping sampling pulses. The model of the proposed scheme is presented to prove its principle and derive its operation conditions. A four-channel scheme with program-controlled pre-filters is demonstrated experimentally, where bandpass filters with the phase shifts of 0°, 90°, 180°, and 270° are synthesized, respectively, by changing temporal shape of the sampling pulses. The experimental results agree well with the theoretical analysis, indicating the validity of the proposed scheme.

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