Optical receiver amplifier with adaptive power and bandwidth for up to 30 Gbit/s in 28 nm CMOS

The design of a receiver (RX) amplifier for optical communications consisting of a transimpedance amplifier (TIA), a six-stage limiting amplifier (LA) with shared inductive peaking, a line driver and an offset compensation loop is presented. The RX is power-bandwidth adaptive, meaning the power can be reduced when a lower bandwidth and data rate (DR) suffices for the transmission meanwhile keeping the gain constant. The circuit was fabricated in a 28 nm, low-power CMOS process and electrical measurements confirmed the functionality of the RX and adaptive concept. Small-signal measurements show a transimpedance gain of 71 dBΩ with 21.5 GHz bandwidth in normal operation (NOP) while 5.95 GHz is achieved in low-power operation (LPO). Large-signal measurements show a clear eye-diagram at 30 Gbit/s in NOP while in LOP 10 Gbit/s can be received. The power consumption reduces from 23.5 mW to 11.5 mW in LPO neglecting the output buffer needed only for measurements. The energy-per-bit is reduced in this way at 10 Gbit/s to 1.1 pJ/bit, from 2.35 pJ/bit which would have been without employing adaptive technique. An output buffer is used for measurement purposes with 14 mW power consumption which is not included in the total power balance. The receiver ranks among the best with the low energy-per-bit of 0.78 pJ/bit at 30 Gbit/s and smallest active area with 6.8 × 10
^-3
mm
²
.