A 64-Gb/s 4-PAM Transceiver Utilizing an Adaptive Threshold ADC in 16-nm FinFET

A 64-Gb/s 4-pulse-amplitude modulation (PAM) transceiver fabricated with a 16-nm fin field effect transistor (FinFET) technology is presented with a power consumption that scales with link loss. The transmitter (TX) includes a three-tap feed-forward equalizer (FFE) (one pre and one post) achieving a level separation mismatch ratio (RLM) of 99% and a random jitter (RJ) of 162-fs rms. The maximum swing is 1.1 Vppd at a power consumption of 89.7 mW including clock distribution from a 1.2-V supply, corresponding to 1.39 pJ/bit. The receiver analog front end (RX-AFE) consists of a half-rate (HR) sampling continuous-time linear equalizer (CTLE) and 6-bit flash (1-bit folding) analog-to-digital converter (ADC) capable of non-uniform quantization. The non-uniform thresholds are selected based on a greedy search approach which allows the RX to reduce power at low channel loss in a highly granular manner and achieves better bit error rate (BER) than a uniform quantizer. For a channel with -8.6-dB loss at Nyquist, ADC can be configured in 2-bit mode, achieving BER <; 1e - 6 at an RX-AFE power consumption of 100 mW. For a -29.5-dB loss channel, the RX-AFE consumes 283.9 mW and achieves a BER <; 1e - 4 in conjunction with a software digital equalizer. For a -13.5-dB loss channel, a greedy search is used to optimize the quantization threshold levels, achieving an order of magnitude improvement in BER compared to uniform quantization.