4-Channel Continuous-Time 77 GSa/s ADC using Photonic Bandwidth Compression

A four-channel continuous-time implementation of photonic bandwidth compression technique is reported. In our approach, which is based on the transient time-stretched analog-to-digital converter (ADC) technology, continuous high speed RF signals arc segmented in the time domain and multiplexed into an array of parallel channels. The segments in each channel are temporally stretched, or equivalently compressed in bandwidth, before digitization. Benefits of our technique include multiplying the effective sample rate and input bandwidth of an ADC. Segments from all 4-channels arc concatenated to form the continuous signal using an out-of-band real-time calibration tone to independently correct for gain and timing errors. In this paper, a 4-channel continuous-time architecture is demonstrated that increases the bandwidth and sampling rate of a state-of-the-art real-time 50 GSa/s digitizer by 55%. A 4-channel system is of particular interest because it matches the number of input channels available on commercial oscilloscopes. The results indicate a viable path to a 4-channel continuous-time system that would be capable of enhancing existing digitizers by more than 300% and achieving 150 GSa/s over 50 GHz in real-time.