A 500 mW ADC-Based CMOS AFE With Digital Calibration for 10 Gb/s Serial Links Over KR-Backplane and Multimode Fiber

This paper presents the design of an analog-front-end (AFE) integrated into a DSP-based transceiver for both serial 10 Gbps KR-backplane and long-reach-multimode-fiber (LRM) applications. The receiver consists of a programmable gain amplifier (PGA) and a 6-bit 4-way time-interleaved ADC, which is digitally calibrated to compensate for the offset, gain and phase mismatches between the interleaved channels. With a 5 GHz input signal, the ADC achieves overall SNDR of 29 dB, while the measured SNDR of flash sub-ADC is 31.6 dB. The power efficiency FoM of the complete interleaved ADC is 1.4 pJ per conversion step. The PLL uses a calibrated LC-VCO and the TX features a full-rate 3-tap de-emphasis at the output. Inductively tuned buffers connected in tandem are employed to distribute the 10 GHz clock. Random and deterministic jitter measured at the TX output are 0.38 ps_rms and 2.65 ps_pp, respectively. Implemented in 65 nm CMOS technology, the AFE occupies an area of 3 mm² and consumes 500 mW from a 1 V supply. BER of less than 10^-15 is measured over legacy backplanes with 26 dB loss at Nyquist and the measured transceiver optical sensitivity is less than -13 dBm for all four LRM stressors, exceeding both the KR and the LRM specifications.