Digitization of RF signals in the GHz range remains a challenge for any technology. Flash ADCs
can digitize signals above 1GHz, but their dynamic range is inadequate for most radio systems.
Semiconductor bandpass Delta Sigma modulators digitize IF signals with high resolution, but their performance at GHz frequencies is limited by comparator delays and the low Q of integrated inductors. Superconducting technology based on Josephson junctions features valuable components for implementing bandpass Delta Sigma modulators: high-Q resonators, multi-GHz comparators, and DACs with naturally quantized output pulses. The superconducting bandpass Delta Sigma modulator presented here achieves the highest center frequency (2.23GHz) and sampling rate (fs=42.6GHz) reported to date. The SNR (49dB over a 20.8MHz bandwidth) is limited by the frequency resolution of the measurement but still exceeds the SNRs of semiconductor modulators with comparable center frequencies.
By: John F. Bulzacchelli, Hae-Seung Lee, James Misewich, Mark B. Ketchen
Published in: RC22154 in 2001
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