Study On Identification And Correction Of Channels Mismatches In Time Interleaved Photonic Analog-to-Digital Converter

Analog-to-digital converter(ADC)is a core device used to convert analog signals into digital signals.It has a wide range of applications in modern digital information processing systems.With the increase in required bandwidth and precision of signal processing,higher and higher sampling rate and sampling accuracy are needed.However,due to the limitation of the electronic bottleneck,it becomes estremely difficult to further improve the performance of the electrical ADC(EADC).The photonic analog-to-digital converter(PADC)makes full use of the advantage in photonic and provides a new way for the acquisition of highfrequency and large-bandwidth signals.Time-interleaved PADC(TIPADC)combines photonic sampling and electronic quantization.As a practical method to realize high sampling rate and precision,it use wavelength division multiplexing(WDM)and optical time division multiplexing(OTDM)to generate sampling pulses and divide sampled signal into multi-channels for parallel processing.This technique can greatly improve the system sampling rate and guarantee the sampling accuracy of a single EADC simultaneously.Because the system is operating in parallel with multiple channels,there will inevitably be a problem of mismatches between channels,that is,inconsistencies in the sampling time,amplitude gain,and DC bias of each parallel channel.The presence of these mismatch factors severely degrades the overall system performance and reduces the effective number of bits(ENOB)of system.Therefore,the identification and correction of channel mismatch and its error become one of the key issues in optical analog-to-digital conversion.In this dissertation,the channel mismatch problem of TIPADC is studied.Based on the existing achievements in the channel mismatch investigation,a channel mismatch identification and correction scheme for TIPADC system including a pre-processing process is proposed and verified via simulation and experiment.Firstly,the basic principle of TIPADC and the system architecture are expounded.The theoretical model of the system is established through the theoretical deduction of the system working process,which provides the basis for the subsequent analysis.Then the theory and the influence of the channel mismatch in the system are analyzed,and the simulation is performed to verify it.In order to integrate the existing achievements in the field,we also analyzed the influence of nonlinearity of the Mach-Zehnder modulator(MZM)on the system performance.A pretreatment scheme was proposed to remove the nonlinearity of MZM and verification is presented by simulation.At the same time the scheme also has the function of removing offset mismatch.Finally,based on the above analysis,we provide a complete analysis model and solution for the two cases of gain and time mismatch.We firstly remove the odd harmonics caused by the MZM nonlinearity through the preprocessing module.The processed signal then enters the correction unit composed of the identification module and the compensation module.The principle of the mathematical derivation is analyzed and the feasibility of the scheme is verified by simulation and experiment.A series of simulation results are given to analyze various factors that affect the performance of the scheme.