Research And Improvement Of A Frequency Interleaving Method For Expanding The Bandwidth Of Sampling System

Multi-channel parallel sampling is a technique widely used in high-speed sampling systems such as oscilloscopes.Time interleaving and frequency interleaving are parallel sampling techniques that have been deeply studied and used at present.However,these two techniques can only increase the sampling rate of the system,but cannot increase the bandwidth.The maximum bandwidth of the system is still limited by the sub-channel analog-to-digital converter(ADC).In order to solve this problem,a series of multi-stage and multi-channel sampling system structures have been proposed.These systems move the high frequency component of the input signal to low frequency by adding a sampler or mixer before the sub-channel ADC,so that the bandwidth of the system is no longer limited by the ADC.Nowadays,mature multi-stage and multi-channel sampling techniques include synchronous time interleaving,asynchronous time interleaving and digital bandwidth interleaving.They are all applied to ultra-high-speed digital oscilloscopes.The goal of this dissertation is to explore new techniques that can increase the bandwidth of domestic oscilloscopes.Because digital bandwidth interleaving(DBI)is less dependent on advanced microelectronics technology,the DBI was chosen for in-depth research.The completed work and important progress are described below.First,the mathematical model of the classical DBI system is established,and the sampling and reconstruction process of the signal is derived.The problems existing in the classical DBI architecture have been pointed out.The problems include the complexity of the software and hardware,which leads to the inability to reconstruct in real time,and the intermodulation of the pilot tone and the input signal to generate spurs.According to problems in the classical architecture,a new synchronous mixing architecture for DBI system is proposed.Digital anti-aliasing filters,digital mixer and the pilot tone insertion system for phase synchronization of the local oscillators between analog and digital mixers can be removed in the new architecture.In the synchronous mixing architecture,only a pair of digital filters are needed to reconstruct the signal,and the software and hardware costs are greatly reduced.Then,an evaluation platform was implemented to compare the performance between the two architectures.It includes radio frequency front-end circuit,synchronous analog-to-digital conversion module,digital signal processing and phase synchronous clock generation system.The system currently uses some low-speed devices for principle verification,but after replacing these devices,it can cooperate with the domestic ADCs to become a high-speed DBI system in the future.In order to accurately obtain the response of the analog front-end circuit of the DBI system during calibration,especially including the sample-and-hold circuit in the ADC,a phase response measurement method based on a phase reference signal without hardware trigger is proposed.At high frequencies,the use of low-cost high-speed phaselocked loop chips to generate a phase reference signal is proposed.To verify the new method,a broadband balun was tested and compared with the results of a vector network analyzer.The result shows that maximum error is about 2°below 8 GHz.Finally,the performance of the classical and synchronous mixing architecture for DBI system was tested and compared.With the same sampling rate of 250 MSPS and bandwidth of 90 MHz,for a 80 MHz input signal,the spurious free dynamic range(SFDR)of synchronous mixing architecture is 24.2 dB higher than the classical one,and the signal-to-noise ratio(SNR)is 2.9 dB higher than the classical one.At the same time,the rise time of the signal is shortened by 0.578 ns on average,and the total order of the finite impulse response(FIR)filter used in signal reconstruction is reduced by about 1/3.When the sampling rate of the synchronous mixing architecture is reduced to 200 MSPS,the rise time of the step signal is still slightly faster than the classical one with a sampling rate of 250 MSPS.The test results show that the new synchronous mixing architecture for DBI system improves performance and reduces costs compared to the classical one.