Research And Design Of 25Gb/s CMOS Optical Receiver Front-end Integrated Circuits

With the rapid development of network communications today,higher requirements are placed on the capacity and quality of communications.Optical communication systems have become the main body of today's information highways due to their advantages in cost and transmission capacity.The core optical communication network are evolving from the era of 100G(4×25G)to the era of400G(16×25G)and more attention will be paid on 25G optical communication systems.Optical receivers are integral parts of optical communication systems.In this thesis,a 25 Gb/s optical receiver front-end is designed,consisting mainly of a preamplifier and a limiting amplifier.The preamplifier mainly includes a transimpedance amplifier and a post amplifier.A feed-forward common gate topology is used for the transimpedance amplifier,which has the advantages such as small input impedance,large bandwidth and low power supply.The post amplifier adopts a three-stage common source amplifier structure with feedback to increase the gain-bandwidth product of the circuit and improve the circuit performance comprehensively.The limiting amplifier mainly includes a core amplifying circuit,a DC offset cancellation circuit,and an output buffer circuit.A third-order interleaving active feedback structure is introduced in the core amplifying circuit to achieve larger bandwidth and smaller gain peaking.The DC offset cancellation circuit eliminates the DC offsets and stabilizes the DC operating point.The f _T doubler is chosen to serve as the output buffer to reduce the parasitic capacitance and ensure enough voltage swing at the output of the limiting amplifier.The optical receiver front-end is designed and simulated in TSMC 65nm CMOS process.The chip area of the circuit is 768?m×366?m.Under the condition of 1.2V power supply voltage and photodiode parasitic capacitance of 80f F,the post-simulation results show that the trans-impedance gain of 77d B,the-3d B bandwidth of 19.3GHz,the input-referred noise current of 39.4p A/sqrt(Hz)at25GHz and the differential output voltage swing of 600m V are achieved.Under various PVT conditions,simulation results show that the optical receiver can work normally.The output eye diagram has good eye opening and small jitter,which can meet the application requirements of the 25Gb/s optical receiver.