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ST418 - Design and Evaluation of Flash ADC (Contest runner-up)

Design and Evaluation of Flash ADC

 Amol Inamdar1, Senior Member, IEEE, Anubhav Sahu1, Jie Ren1,
Sormeh Setoodeh2, Raafat Mansour3, Fellow, IEEE, and
Deepnarayan Gupta1, Senior Member, IEEE

1HYPRES, Inc., 175 Clearbrook Rd., Elmsford, NY 10523, USA
 2Avago Technologies, 350 W. Trimble Road, San Jose, CA, 95131
3Electrical and Computer Engineering Department, University of Waterloo,
Waterloo ON N2L 3G1, Canada

Email: [email protected]

Abstract — We have designed single-bit comparators and multi-bit flash ADCs using three flavors of periodic comparators; one flavor uses a differential “quasi-one-junction” SQUID (DQOS) comparator, the second use a differential SQUID wheel comparator and the third uses a symmetric differential SQUID wheel comparator with time-interleaved clocks. We have also developed a new performance analysis scheme that enables full reconstruction of input signal using a single-bit comparator. The signal is reconstructed based on multiple beat frequency measurements that track the position of the comparator thresholds in response to a DC offset to the input signal. In addition, to eliminate the frequency dependent distortions resulting from impedance mismatches over wide bandwidths, the signal and clock distribution network have been optimized using EM simulations. For distributing the clock signal to the multi-bit comparators, a 50 ohm coplanar transmission line has been designed. Test results for a 1-bit comparator using a differential SQUID wheel comparator demonstrates a performance of 4.5 bits of resolution in Gray code for a beat frequency test using a 20 GHz input signal and 5.3 bits for 10 GHz input. 4-bit and 8-bit versions of the flash ADC with a DQOS comparator and a 3-bit time-interleaved ADC using the SDSW comparator have also been designed. The DQOS ADC has been tested up to 25 GHz input signal frequency with performance of 4.3 bits of resolution in Gray code for 19.7 GHz input signal. The time-interleaved ADC performance is 4.3 bits for a 15 GHz beat frequency test with an effective sampling rate of 30 GHz.

Keywords (Index Terms) — Flash ADCs, periodic comparators, Analog-to-Digital Converter, SQUID Wheel.

IEEE/CSC & ESAS SUPERCONDUCTIVITY NEWS FORUM (global edition), January 2015.
September 17, 2014; Selected September 29, 2014. Reference ST418; Category 4.
ASC 2014 manuscript 4EPo1A-02 published online in IEEE Trans. Appl. Supercond. (IEEE XPLORE) DOI: 10.1109/TASC.2014.2365717, on October 29, 2014.