| With rapid development ofvirtual reality,Internet of Things and cloud computing,the global data volume grows explosively in the past two decades.Therefore,higher transmission ratesof data centerare required.Sincethecopper-based electrical interconnect is limited by crosstalk,electromagnetic interference and high-frequency loss,optical interconnect becomes the best current solution to handlethe high data traffic with features of wide bandwidth and low loss.Recently,the need of data centers has already exceeded50Gb/s data rate.The traditional non-return-to-zero(NRZ)signal is losing its attraction due to the limitations of power consumption and system complexity.The four-level pulse amplitude modulation(PAM4)scheme with doubled bandwidth efficiency has become the most promising solution for nextgeneration optical transceiver.Although great progress has been made in the design of PAM4optical receiver,many technical difficults still need to be solved.Especially,the jitter and output swing of output signal in the mixed-signal receivers need further optimization.Aiming at the technical difficults existing in the PAM4 optical receiver.This thesis analyzed the key parameters that affect the performance of PAM4 optical receiver,optimized the optical receiver architecture,and a transimpedance amplifier and PAM4 optical receiver are designed in detail.The specific work contents are as follows:Firstly,this thesis analyzed the advantages and disadvantages of the current PAM4 receiver solutions,and proposed an improved PAM4 receiver solution based on mixed-signalconfiguration.The PAM4 signal is received by atransimpedance amplifier,then it is converted into a thermometer code by the combination of a level shifter and a limiting amplifier,and the thermometer code is restoredto NRZ signals by a high-speed decoder.Secondly,based on UMC 0.18μm CMOS process,a transimpedance amplifier for PAM4 receiver was designed.By combining a RGC amplifier,a parallel feedbackamplifier and aπ-type matching network,the input-referrednoise current was successfully reduced.The results showed that the designed TIA had a transimpedance gain of 59.5 dBΩand a-3 dB bandwidth of 4 GHz.Meanwhile,the average input-referred noise current spectral density within the interesting bandwidth was less than 7 pA/√(Hz).The chip can transmit 5 Gb/s NRZ signal and 8 Gb/s PAM4 signals.Finally,a PAM4 optical receiver was designedbased on IHP SiGeBiCMOS 0.13μm process.By redesigningconventional Cherry-Hooperamplifier,the bandwith and gain of limit amplifier have been significantly improved.A CML-based sampling circuit was applied to reduce the jitter of signal,which is caused by different transition time of PAM4 signal.The simulation results showed that the input and output impedance of our designed circuit match well,and the circuit can correctly restoretwo25 Gb/s NRZ signals.The eye diagrams of the two signals are clear.The jitter is respectively 3.2ps and 4.1 ps,which is less than 0.11 UI,and the output swing amplitude is 0.6 V.The chip area is only 0.88 mm~2. |
