Based On The Characteristic Impedance Of Equivalent Pseudo Differential Test Technology And The Implementation

Time domain reflectometry (TDR) is a testing instrument based on the time domain reflection theory. The theory refers to the signal propagating in the transmission path will produce a reflected signal back to the source end while encountering the discontinuous points. Then the informations of the discontinuous points can be analyzed through the reflected signals. With the rapidly increase of the clock frequency and data rate, the signal integrity issues of the PCB are becoming more and more serious. Now TDR is the most straightforward way to measure the characteristic impedance in PCB industry fileds, because of the accuracy, intuitiveness and richness of this method.Due to the advantages, differential-impedance circuit boards are becoming more and more common in the digital circuit designs. So the time domain reflectometry needs to be able to measure the differential impedance. Till now the foreign TDR instruments have monopolized all over the world in the test market of characteristic impedance. Instead, the researches of the TDR instruments in china are still in its early stage. So there is an urgent need to design the TDR instruments with single and differential impedance measurements. In this dissertation, the realization of the differential impedance measurements in TDR instrument is introduced based on the single impedance measurements.Firstly, the significance and background of the research of TDR are introduced in this thesis, also are the basic principles of TDR test based on the theory of transmission line. Then the design index and the overall design scheme of the hardware are put forward, and the overall frameworks of the system are introduced.Secondly, the Data Acquisition System is introduced. On the analysis of the basic ways of sampling methods, the sequence-equivalent sampling method is used in this ADC system. Though this way, the collection and reconstruct of the high bandwidth signal with a low sampling rate are realized. Then the performance of the ADC system is tested, including the SNR and SINAD.Thirdly, based on the basic differential-impedance measurement methods, the equivalent pseudo-differential method is put forward. In this way, single pulse sourcer and single sampler can measure the differential impedance. And the hardware design is simplified without reducing the accuracy of the measurement. Then based on the multiple reflections algorithm, the influence factors and the formula of the equivalent pseudo-differential method are proposed and verified. At last, the calibration method and steps of the differential-impedance measurement are recommended, on the basis of the sigle-ended measurement.Finally, the design of the FPGA is introduced, including the circuit, the control program and the design of FIR digital filters as the data pretreatment method. At last it gives a comparison on the results of the single-ended and differential characteristic impedance measurements with the Polar’s instruments.