UCLA

With the recent surge in the demand for high data rates, communication over copper media faces new challenges. First, the limited bandwidth removes so much of the signal's high-frequency energy that equalization and detection become very difficult. Second, the greater data rates in serial links inevitably translate to high power consumption. State-of-the-art transmitters operating in the range of tens of gigabits per second draw hundreds of milliwatts, underscoring the need for new circuit and architecture techniques that can ease the trade-off with speed.

The first part of this research introduces a 40-Gb/s non-return-to-zero transmitter that improves the power efficiency by a factor of 2.28. This is accomplished through removing power-hungry retimers in transmitter front end, merging the output driver and the final multiplexer stage, proposing a current-integrating multiplexer and "latchless" feedforward equalization path. Implemented in 45-nm CMOS technology, the transmitter provides 7.4-dB boosting and draws 32 mW at 40 Gb/s.

The second part of this research studies the design of an 80-Gb/s PAM4 transmitter that achieves nearly six-fold improvement in power efficiency with respect to state of the art. With a two-fold reduction in bandwidth occupancy compared to non-return-to-zero data, the PAM4 format allows significant speed improvement but also introduces other issues such as skew and linearity. The design introduces a number of novel ideas so as to achieve both a very high data rate and much lower power consumption compared to state of the art. In particular, the design proposes a "latchless" serializer architecture, a charge-steering multiplexer, and a high-speed divide-by-two circuit that directly generates outputs with a 25% duty cycle. These techniques culminate in the 80-Gb/s PAM4 transmitter, including an on-chip phase-locked loop, that draws only 44 mW in 45-nm CMOS technology.