Design of a Direct Transfer Function Measurement System based on an SID Algorithm and GPIB Instruments

• Main Authors: Hsing-Kai Chen, 陳信凱
• Other Authors: Chung-Lin Huang
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/72450166050437985662

碩士 === 國立清華大學 === 電機工程學系 === 87 === Traditionally measuring the TF (transfer function) of an analog circuit often adopts the step sine method in which the CUT was scanned across the specified frequency range by one sine wave at a time. This result is quite precise, but the phase information can not be measured easily in this procedure, and the measuring time is proportional to the range of scanning bandwidth. In this paper, we propose a system for the automatic FRF (frequency response function) measurements to overcome the drawbacks of the aforementioned method. In this system, several GPIB instruments, including an arbitrary waveform generator (HP33120A), a digital storage scope (Tektronix TDS220), a spectrum/network analyzer (HP3589A), a PC and the CUT are used. The measuring developed under LabWindows /CVI environment contains the driver of those instruments, a proposed S.I.D. algorithm and display programs. Careful selection of the input excitation to the measuring system is a key factor for the measuring performance. This paper analyzes different input sequence and adopts the MLBS as the input sequence during measurements. Several algorithms for estimating the FRF are also evaluated. In addition to estimating the FRF in frequency domain, the time domain knowledge is also utilized. An optimal search method for the most proper length of the impulse response is used in the measuring system. The FRF of two circuits, namely notch and low-pass filters are measured under the SID algorithm. The results show that the SID algorithm has a better accuracy and smaller RMS error compared to other methods such as H1、Hlog、Hv…..etc. The resolution and speed of the proposed measuring system can be improved by using high precision DSO and AWG.