Research And Development Of A 20 Gb/s PAM4 Optical Communication ASIC In High Energy Physics Experiment

The large-scale High Energy Physics experiment detector is an important scientific device to study the origin and fundamental composition of the universe and the interactions among matter.Processing and transmitting the massive amount of recorded data from these large scientific installations is a great challenges for existing data communication systems.High-speed optical fiber links are commonly used in modern high-energy physics experiments to transmit large-volume data from detectors to control rooms for further analysis.The confined space and harsh radiation environment that detectors are subject to make it impossible for commercial devices to be used directly,so experimental physicists develop optical transmission ASICs(application-specific integrated circuits)and optical modules to meet their system requirements.The optical transmitter ASIC lpGBT and module VTRx+have achieved a maximum data rate of 10 Gb/s.Future high-energy physics experiments have a great demand for high-bandwidth and low-power optical fiber transmission systems.Under this background,this dissertation explores and investigates the scheme of next-generation radiation-tolerance over 10 Gb/s optical data transmission link,focusing on the development of a 20 Gb/s radiation-tolerant optical fiber link at chipand module-level,based on the 4-level pulse amplitude modulation(PAM4)technology.This customized PAM4 optical link mainly includes three parts:the transmitter ASIC GBS20,the optical transmitter module GBT20,and the optical receiver ASIC GBDS20.This dissertation focuses on presenting the design and test results of GBS20.A dualchannel serializer shares the same clock system in the die,and the PAM4 encoding of the data is achieved through the differential combiner to improve the data rate.There are 16 user interfaces to the GBS20 chip.Each user channel has a built-in phase aligner to ensure that the data is always correctly sampled.The user data is scrambled in the encoder,and an appropriate header is added for the back-end to receive and decode the serial stream.The library of radiation tolerant technology developed by CERN is adopted in the digital circuit and triple-modular redundancy is used to reach the radiation tolerance level in the crucial circuit and sensitive nodes of the ASIC.Irradiation tests find no single-event effect after fluence of 8.6×1013 protons/cm2 with a 400 MeV proton beam,and no obvious performance degradation after a total ionizing dose of 35 kGy.The GBT20 optical module has been fabricated,and the test will start soon.In order to verify the integrity of the optical fiber link as soon as possible,the receiver chip GBDS20 TIA uses two-stage differential trans-impedance amplifiers to realize a linear transmission of PAM4 signals.The simulation results are consistent with expectations.The major works and innovations of this dissertation are as follows:1.Applying the PAM4 encoding technology in the field of optical data transmission for high energy physics experiments,for the first time.A 20.48 Gbps transmitter chip was successfully implemented with a 65 nm CMOS technology.And the transmission rate is twice that of lpGBT,the fastest data transmission chip in the field.2.The data serializer and the VCSEL laser driver are integrated together.One GBS20 chip will replace the conventional two chips,simplifying the data transmission design architecture.3.Proposed and designed a 20.48 Gb/s PAM4 receiver ASIC.The preliminary simulation results show that the scheme is highly feasible,and the output signal can be received by PAM4 enabled FPGAs,realizing the closed-loop transceiver of the 20 Gb/s PAM4 optical data link.4.Proposed and implemented a variety of PAM4 transmitter optical module designs(GBT20).The VCSEL bias circuit is integrated into the GBS20 ASIC,which directly drives a VCSEL in a die form or in a TOS A.The ASICs which related to the optical link at the transmitting end can be integrated into the same high-density and small-sized optical module.The maximum height of the GBT20 optical module is 5.75 mm,which meets the requirement of most high-energy physics experiments for the optical module size.The optical link based on the PAM4 technique is an effective strategy to overcome the bandwidth limit of the current technology.In the long run,even when more advanced technology is adopted in the field of subsequent high-energy physics experiments,the research and the design method described in this thesis will still have significant reference value for the research and development of high-speed data transmission,providing an important development direction for the subsequent upgrade of optical fiber links.