A 0.47–0.66 pJ/bit, 4.8–8 Gb/s I/O Transceiver in 65 nm CMOS

A low-power forwarded-clock I/O transceiver architecture is presented that employs a high degree of output/input multiplexing, supply-voltage scaling with data rate, and low-voltage circuit techniques to enable low-power operation. The transmitter utilizes a 4:1 output multiplexing voltage-mode driver along with 4-phase clocking that is efficiently generated from a passive poly-phase filter. The output driver voltage swing is accurately controlled from 100–200 ${\rm mV}_{\rm ppd}$ using a low-voltage pseudo-differential regulator that employs a partial negative-resistance load for improved low frequency gain. 1:8 input de-multiplexing is performed at the receiver equalizer output with 8 parallel input samplers clocked from an 8-phase injection-locked oscillator that provides more than 1UI de-skew range. In the transmitter clocking circuitry, per-phase duty-cycle and phase-spacing adjustment is implemented to allow adequate timing margins at low operating voltages. Fabricated in a general purpose 65 nm CMOS process, the transceiver achieves 4.8–8 Gb/s at 0.47–0.66 pJ/b energy efficiency for ${\rm V}_{\rm DD}=0.6$ –0.8 V.