Memorias de investigación
Communications at congresses:
Real Time FPGA-based Crosstalk Elimination for Multichannel Interferometry Systems in Fusion Diagnostics

Research Areas
  • Design of integrate circuits to reshape circuitry

Infrared (IR) interferometry is a well-known method for measuring the Line-Integrated electron Density (LID) of fusion plasmas. In the TJ-II stellarator, an FPGA-based IR- interferometer has been recently installed to accurately measure the LID of the plasma in real time. To guarantee the correct functionality of the interferometer and achieve high precision rates, it is essential to maximize the Signal-to-Noise Ratio (SNR) of the output density signal. In the measurement process, one of the most important distortion sources is the crosstalk or interchannel interference. Thus, in order to increase the SNR of the system, a crosstalk reduction stage has been designed and implemented in the FPGA. This paper shows a novel crosstalk elimination algorithm that has been optimized for its high-performance hardware implementation. Since the algorithm operates over the complex spectrum of the signals, the N-point Fast Fourier Transform (FFT) is initially performed. Afterwards, the inner product between the spectrums is used to reconstruct an estimation of the transfer function of the interfering system and this reconstruction is used to eliminate the interference in the frequency domain. Finally, the N-point inverse FFT is carried out to obtain an improved version of the time signal required in the phase detection block. In addition, an M-factor pre-downsampling stage has been included to increase the frequency resolution of the algorithm. This stage down-converts the input signals into low frequency aliases, which decreases the sample frequency as the overall system resolution is signi?cantly increased. This procedure in combination with the existing phase detection algorithm performs the required operations in a few microseconds, which allows extracting an accurate mea- surement of the LID in real time, and enables the capability of controlling the heating systems of the reactor using a feedback loop. This is possible because the algorithm is implemented as a pre-processing stage, in contrast with the tendency of existent algo- rithms which are usually applied in post-processing, obtaining better results eliminating the interference as soon as the signal is detected.
IEEE 18th Real Time Conference, RTC'12
Berkeley (California, USA)
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Proceedings of IEEE 18th Real Time Conference
  • Autor: Sergio Hernández Universidad Politécnica de Madrid
  • Autor: Juan Antonio Lopez Martin UPM
  • Autor: Miguel Sánchez CIEMAT
  • Autor: Luis Esteban CIEMAT

Research Group, Departaments and Institutes related
  • Creador: Grupo de Investigación: Laboratorio de Sistemas Integrados (LSI)
  • Departamento: Ingeniería Electrónica