Nuclear Techniques ›› 2015, Vol. 38 ›› Issue (3): 30102-030102.doi: 10.11889/j.0253-3219.2015.hjs.38.030102


Calibration method and experiment based on I/Q demodulation principle

ZHANG Zhigang1,2,3 ZHAO Yubin1,3 XU Kai1,3 ZHENG Xiang1,3 LI Zheng1,3 ZHAO Shenjie1,3 CHANG Qiang1,3 HOU Hongtao1,3 MA Zhenyu1,3 LUO Chen1,3 MAO Dongqing1,3 SHI Jing1,3 WANG Yan1,3 LIU Jianfei1,3   

  1. 1(Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Jiading Campus, Shanghai 201800, China) 2(University of Chinese Academy of Sciences, Beijing 100049, China) 3(Shanghai Key Laboratory of Cryogenics & Superconducting RF Technology, Shanghai 201800, China)
  • Received:2014-11-19 Revised:2014-12-12 Online:2015-03-10 Published:2015-03-09

Abstract: Background: In-phase/Quadrature (I/Q) demodulation technology is widely used in radio frequency signal phase control system. As the intrinsic errors in hardware, such as the imbalances of gain and phase in 90° hybrid and 0° hybrid, direct current (DC) offsets and phase errors from length difference of circuits, the output signal is an ellipse and the output phase is nonlinear to the input radio frequency (RF) signal. The detection of phase precision is influenced. Purpose: This study aims to reduce the effects of errors existed in the I/Q demodulators. Methods: A calibration method for I/Q demodulation technique is proposed and applied to research and development of I/Q integrate circuits, which is based on the surface mounted devices (SMD) chip. Results: Experimental tests showed that the phase error was less than ±0.15°, the amplitude stability was less than ±1%, and the channel delay was less than 10 ns. Conclusion: This calibration method, together with the designed circuit board for the RF signal front end preprocessing can reduce the effects of intrinsic errors efficiently. It has been being used in upgrading of beam trip diagnostic system in the storage ring of Shanghai Synchrotron Radiation Facility (SSRF).

Key words: In-phase/Quadrature (I/Q) demodulation, Amplitude imbalance, Phase imbalance, Calibration