Radiation-tolerant Laser Driver ASICs For ATLAS Front-end Readout System

ATLAS,a large universal detector,is an important part of the famous Large Hadron Collider(LHC)in high-energy physics experiments at present.When high-energy physics experiments are carried out,the particle irradiation effect is generated by the collision of highly energetic particles,resulting in the front-end system of ATLAS detector prolonged ex:pose in high intensity radiation environments.Since commercial chips could not work in irradiated environments,radiation-tolerant Application Specific Integrated Circuits(ASICs)will play an important role in the front-end systems of ATLAS detectors.With the upgrading of the LHC,it not only greatly improves the energy and brightness of the ATLAS detector,but also brings a huge amount of data information.ATLAS liquid argon(LAr)calorimeter which is in the ATLAS detector front-end readout system is used to quickly and reliably read and transmit this large amounts of data measured in the experiment.The optical fiber link using as its data transmission module could greatly improves the data transmission efficiency and it is an important research area.This dissertation describes the design of the ASIC series of dual-channel laser driver for optical fiber transmission transmitters in high energy physics experiments.The series of chips,named LOCId,act to receive encoded serial data and convert them into modulated current to drive the Transmitter Optical Subassembly(TOSA)for electro-optical conversion.In this dissertation,three anti-irradiation LOCld chips are introduced.They are LOCld2-250 LOCld2-130 and LOCld2-65.LOCld2-250 has been designed basing on the 250-nm Silicon on Sapphire(SoS)CMOS process and used in ATLAS LAr calorimeter readout Phase-I upgrade;LOCld2-130 is a upgraded version of LOCId2-250 and was designed on the 130-nm IBM CMOS process;LOCld2-65 was based on the 65-nm TSMC CMOS process and it is a high-speed version that may be used for LpGBT project.The research contents and innovations of this dissertation are mainly manifested in the following aspects:Firstly,as an upgraded version of LOCld2-250,LOCld2-130 has the same performance requirements as LOCld2-250.Their channels are required to receive 5.12-Gbps 2-mA CML signals and output 5.12-Gbps 8-mA modulation currents.However,the channel structure in the LOCld2-130 is much simpler than LOCld2-250,which greatly reduces the total power consumption.In the LOCld2-250,the analog channel employs a six-stage Limiting Amplifier(LA)to provide a high gain,and uses an active inductor shunt peaking to extend the bandwidth.The channel structure is complex and requires an additional higher power supply.While in the LOCld2-130 analog channel design,it only uses a two-stage LA.And these two stages share an inductor to boost the bandwidth.The structure do not need an additional power supply,which can simplify Printed Circuit Board(PCB)design.In order to resist the Total Ionizing Dose(TID)effect,we use a constant current source bias circuit in the LOCld2-250 channel which can enhance the ability of anti-radiation.However the bias requires an external resistor which means more pins are needed.In LOCld2-130,we proposes a bias circuit that can keep the common-mode voltage of LA and also equip with anti-radiation capability.Moreover,it does not need ane external resistor.Secondly,LOCld2-65 is the highest-speed dual-channel laser driver for TOSA in the current high-energy physics field.its operating rate is 14 Gbps per channel and the minimum input signal is 1 mA.Therefore,the design is much more complicated than the other two chips.In the analog channel,both the input amplifier and the output driver add an adjustable linear equalizer to compensate the attenuation of the high frequency components of the signal.The pre-driver adopts four-stage LA to provide sufficient gain;each two stages share a three-tapped inductor to extend bandwidth.We also add an adjustable negative feedback loop between the second stage and the fourth stage of the pre-driver to ensure the gain and the bandwidth meet the requirements in all Process Voltage Temperature(PVT)cases.By adjusting the feedback strength,the gain of at the fast process case is increased,and the bandwidth at the slow process case is expanded.Thirdly,In order to test LOCld65,we improved the Miniature Optical Transmitter(MTx)and it was named MTx+.We made the two improvements in MTx+.We adopted the standard Enhanced Small Form-factor Pluggable(SFP+)connector in the MTx+ to support hot-plug and designed a custom optical latch to hold a PCB,two standard LC connectors,and the two TOSAs together.At present,the design of LOCld2-130 has been completed and verified by post-layout simulation.But it does not be taped out.The simulation result shows that at the typical case the total power consumption of single channel is about 59.9'mW,which is much lower than LOCld2-250.The LOCld2-65 has been tapped out.Four pieces of LOCld2-65 chips have been embedded into the optical modules and passed optical test.We compare the test results with the simulation results,they are basically the same.Since the TID irradiation test took a long time,only one chip has been tested for TID irradiation.The results show that when the total dose reaches 4.9 kGy(Si02),the performance of the chip remain basically unchanged.So far the lab still look for an opportunity to test the Single event upset(SEU).