在光接收电路设计中,光电二极管的寄生电容以及大的输入电阻会导致接收机带宽下降,造成严重的符号间干扰(Inter-Symbol Interference,ISI).噪声性能是高速跨阻放大器(Transimpedance Amplifier,TIA)最重要的指标之一,跨阻值决定系统的噪声性能,同时也限制了数据速率.针对100G/400G互补金属氧化物半导体(Complementary Metal Oxide Semiconductor,CMOS)光接收机应用,基于 45 nm 绝缘衬底上的硅(Silicon-On-Insulator,SOI)工艺设计了一种采用四电平脉冲幅度调制(4-level Pulse Amplitude Modulation,PAM-4)、工作速率为56Gbit/s(28Gbaud/s)的低噪声光接收机前端放大器.小带宽TIA和用于带宽拓展的跨导/跨导(gm/gm)放大器组成两级接收前端,在改善噪声性能的同时有效提高了带宽.采用反相器结构来增大先进CMOS工艺下的跨导和改善线性度.可变增益放大器(Variable Gain Amplifier,VGA)采用折叠Gilbert结构设计,采用并联峰化电感来提高带宽.整体电路的增益动态范围为51.6～70.6dB,-3dB带宽达到20.1 GHz;等效输入噪声电流密度为17.3pA/Hz1;电路采用GF45nmSOICMOS工艺实现,在1.1 V和1.3 V电源电压下功耗为65mW;版图核心面积为600μm*240μm.
Design of a 56 Gb/s PAM-4 optical receiver front-end in 45 nm SOI CMOS
In optical receiver design,the parasitic capacitance of the photodiode and the large input resistance will reduce the bandwidth of the receiver,causing serious inter-symbol interference(ISI).Noise is one of the most important metrics of the high-speed transimpedance amplifier(TIA),and the transimpedance value determines the noise performance of the system while also limits the data rate.An optical receiver front-end based on 45 nm Silicon-On-Insulator(SOI)process for 4-level Pulse Amplitude Modulation(PAM-4)working at 56 Gbit/s(28 Gbaud/s)is presented tailored to 100G/400G optical receiver applications.A low-bandwidth TIA and a gm/gm amplifier for bandwidth expansion form a two-stage front-end that improves noise performance while effectively expanding bandwidth.The inverter structure is used to increase transconductance and improve linearity in advanced Complementary Metal Oxide Semiconductor(CMOS)technology.The variable gain amplifier(VGA)is designed with a folded Gilbert structure and uses a parallel peaking inductor to expand bandwidth.The dynamic range of the overall circuit is 51.6 dB to 70.6 dB,and the-3 dB bandwidth reaches 20.1 GHz.The input referred noise current density is 17.3pA/Hz/2.The circuit is implemented in GF 45 nm SOI CMOS,dissipating 65 mW of power from 1.1 V and 1.3 V supply.The layout core area is 600 μm*240 μn.
万方数据
