A new IQ detection method for LLRF

Summary, in English

Digital LLRF technology has been widely used in new generation particle accelerators. IF quadrature sampling is a common method for amplitude and phase detection. Many strategies, which obey the same rule of f(sample) = (M/N)f(IF) (M/N is a rational number), have been proposed to reduce the effects of spectrum aliasing. However, we found that M/N does not need to be a rational number according to Shannon's theorem. Therefore, we propose a new IQ detection method in this paper. This method is based on a special IIR filter which is derived from an RLC circuit. The unique characteristic of the method is that the value of f(IF) is independent of the value of, f(sample). We have set up an experimental platform to verify our method. A 122.88 MHz sampling clock is used to sample a 3 MHz IF signal. The DOS and PI control techniques are used to realize the closed-loop control. Results show that the stability of the system is within +/- 0.05% (peak to peak) for the amplitude, and with +/- 0.03 degrees (peak to peak) for the phase in 5 h. (C) 2012 Elsevier B.V. All rights reserved.

• Author: Feng Qiu; Jie Gao; Hai-ying Lin; Rong Liu; Xin-peng Ma; Peng Sha; Yi Sun; Guang-wei Wang; Qun-yao Wang; Bo Xu; Rihua Zeng
• Department/s: European Spallation Source ESS AB
• Publishing year: 2012
• Language: English
• Pages: 139-143
• Publication/Series: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment
• Volume: 675
• Links: http://dx.doi.org/10.1016/j.nima.2012.01.068
• Document type: Journal article
• Publisher: Elsevier
• Topic: Accelerator Physics and Instrumentation
• Keywords: LLRF; IQ detection; IIR filter; RLC circuit; DDS
• Status: Published
• ISBN/ISSN/Other: ISSN: 0167-5087