Design Of 4×28Gbaud/s PAM4 Laser Driver Integrated Circuit

With the rapid development of 5G technology industry,the ever-increasing data exchange throughput makes high-speed optical fiber communication flourish,and its application in base stations is also increasing.The application of high-speed transmission system is more and more extensive,and the application of high-speed optical fiber communication in base station is also increasing day by day.Four Pulse Amplitude Modulation(PAM4)technology improves the data transmission volume of interconnected channels by increasing the amount of information carried by each baud,and responds to the bandwidth requirements of today’s high-speed optical fiber communications.This paper studies the laser driver part of the optical communication system.The laser driver is located at the last end of the optical transmitter and is used to amplify the output signal of the multiplexer and convert the electrical signal input light source into an optical signal output.Because vertical cavity surface emitting laser(VCSEL)has the characteristics of low power consumption,small size and low cost,the optical communication system usually selects VCSEL as the light source.The VCSEL driver designed in this paper is the key module of the optical transmitter,which is located at the end of the optical transmitter.This paper uses 0.18μm Si Ge BiCMOS technology to research and design the VCSEL driver.The designed driver includes variable gain amplifier,continuous-time linear equalizer and main driver stage.It also contains pre-emphasis and de-emphasis technology and current rudder digital-analog converter.Group delay peak-peak value and bandwidth bottleneck from VCSEL are challenges to achieve high speed optical interconnect at 28Gbaud/s bauds rates and above.This paper presents a PAM4 VCSEL-based Optical Transmitter that employs 3-tap feedforward equalizer(FFE)and continuous time linear equalizer(CTLE)to overcome these problems.By utilizing two pre-emphasis taps and CTLE,bandwidth of this system is extended.Moreover,peak-peak value of group delay for this system is reduced to 3.7ps by using one de-emphasis tap.The layout of the 4 × 28 Gbaud / s PAM4 optical transmitter laser driver circuit designed in this paper is 1.5mm × 1.95 mm.The post-simulation results show that the-3d B bandwidth can reach a minimum of27.6GHz.When the input voltage range is 200 m V-400 m V differential,the output bias current coverage range is 2.1-5.6m A,and the output modulation current coverage range is 1.6m A-7.6m A,The group delay deviation is less than ± 0.1UI,the linearity is less than 3%,the static total power consumption is less than230 m W,the post-simulation results of each index meet the original design goals,and the margin is sufficient and the performance is good.