一种高速大电流的PAM4光发射机设计

Design of a high-speed PAM4 optical transmitter with large current

随着通信数据比特率不断提升,PAM4(四阶脉冲幅度调制)光发射机已经在超高速光纤通信系统中得到更广泛的应用。设计了一种包含NRZ(非归零)编码-RZ(归零)编码转换电路的PAM4光发射机,基于电流模逻辑增加了电路的工作速度和抗干扰能力。通过带自偏置可控延时电路实现了NRZ编码到RZ编码的转换,减小了长链路信号传输的色散效应。驱动器采用预驱动与主驱动级联的方式增大电路驱动能力,并通过串联电阻实现级间的共模电平匹配。电路设计采用0.13μm SOI CMOS工艺,仿真结果表明在两路输入数据比特率为2.5 Gb/s,典型负载为25Ω时,最大输出电流为120 mA,电流脉冲宽度为125 ps,PAM4眼图张开度良好。

With the continuous improvement of the communication data bit rate, PAM4 (four-level pulse amplitude modu-lation) optical transmitters are more widely used in ultra-high-speed optical fiber communication systems. A PAM4 opti-cal transmitter including NRZ (non-return-to-zero) encoding to RZ (return-to-zero) encoding converter is designed in this paper. Based on current mode logic, it increases the circuit ′ s working speed and anti-interference ability. The self-biased controllable delay circuit is used to realize the converter from NRZ encoding to RZ encoding, which reduces the dispersion effect of long-link signal transmission. The driver uses a cascade of pre-driver and main driver to increase the driving capability, and achieves common-mode level matching between stages by a series resistor. The circuit design is based on 0. 13 μm SOI CMOS process. Simulation results show that the maximum output current is 120 mA, the cur-rent pulse width is 125 ps, and the PAM4 eye pattern is open well at an input data rate of 2. 5 Gb/s and a typical load of 25 Ω.