Near-Optimal Equalizer and Timing Adaptation for I/O Links Using a BER-Based Metric

• Published in: IEEE journal of solid-state circuits Vol. 43; no. 9; pp. 2144 - 2156
• Main Authors: E-Hung Chen, Jihong Ren, Leibowitz, B., Hae-Chang Lee, Qi Lin, Kyung Oh, Lambrecht, F., Stojanovic, V., Zerbe, J., Yang, C.-K.K.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.09.2008; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Adaptation; Algorithms; Applied sciences; Bit error rate; bit error rate (BER); CDR; Circuit properties; Decision feedback equalizers; Electric, optical and optoelectronic circuits; Electronic circuits; Electronics; equalizer; Exact sciences and technology; Filters; Frequency filters; I/O link; Intersymbol interference; ISI; Power generation; pre-cursor; Sampling methods; Studies; Testing; Timing; Transmitters; Voltage; Performance evaluation; pre-cursor; Output power; Bit error rate; Transmitter; Receiver; Decision feedback equalizers; bit error rate (BER); I/O link; Clock recovery; CDR; Digital filter; Intersymbol interference; Data recovery; equalizer; Finite impulse response filter; Objective function; Sampling; Peak power; ISI; Least mean squares methods; Adaptation
• ISSN: 0018-9200; 1558-173X
• DOI: 10.1109/JSSC.2008.2001871

A new adaptation strategy of I/O link equalizers is presented based on minimizing the bit error rate (BER) as the objective function to maximize the receiver voltage margin. The adaptation strategy is verified in a 90-nm test chip on both the transmitter finite-impulse response filter (Tx-FIR) and the receiver decision-feedback equalizer (Rx-DFE). The performance is compared with the commonly used sign-sign least mean square (SS-LMS) adaptation and demonstrates significant improvements especially in the case of the Tx-FIR. This paper also demonstrates that in a highly attenuating system that contains both a Tx-FIR and Rx-DFE, using a Tx-FIR subject to peak output power constraint to compensate pre-cursor ISI is worse than solely using an Rx-DFE. The adaptation strategy is further applied to adapt the sampling phase of the clock-and-data recovery loop (CDR). The technique enables near-optimal BER performance by substantially reducing the pre-cursor ISI and requires almost no additional hardware compared to SS-LMS adaptation.