Digital detection and processing of multiple quadrature harmonics for EPR spectroscopy
Digital detection and processing of multiple quadrature harmonics for EPR spectroscopy
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DOI：
10.1016/j.jmr.2010.09.016
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发表时间：
2010-12-01
影响因子：
2.2
通讯作者：
Potter, L. C.
中科院分区：
文献类型：
--
作者：
Ahmad, R.;Som, S.;Potter, L. C.
报道了一种用于l波段电子顺磁共振（EPR）光谱的正交数字接收机及其信号估计程序。该方法可同时采集和联合处理同相和非相通道中的多个谐波。数字接收机，基于高速双通道模数转换器，允许直接数字下变频外差处理使用微波参考信号的数字捕获。因此，接收器避免了与模拟混频器相关的噪声和非线性。此外，该架构允许低q抗混叠滤波，并且不需要采样频率被时间锁定到微波参考。提出了一个适用于振荡器相位噪声任意贡献的噪声模型，并给出了相应的未知参数的极大似然估计。该信号处理方法适用于非饱和条件下的洛伦兹线形。在存在相位噪声和未知微波相位的情况下，采用一种能够联合处理同相和异相数据的收敛迭代算法进行估计。Cramer-Rao界分析和仿真结果表明，无论相位噪声值高还是低，使用正交检测都能显著降低线宽估计误差。本文还报道了EPR光谱数据以作说明。(C) 2010爱思唯尔公司版权所有。
A quadrature digital receiver and associated signal estimation procedure are reported for L-band electron paramagnetic resonance (EPR) spectroscopy. The approach provides simultaneous acquisition and joint processing of multiple harmonics in both in-phase and out-of-phase channels. The digital receiver, based on a high-speed dual-channel analog-to-digital converter, allows direct digital down-conversion with heterodyne processing using digital capture of the microwave reference signal. Thus, the receiver avoids noise and nonlinearity associated with analog mixers. Also, the architecture allows for low-Q anti-alias filtering and does not require the sampling frequency to be time-locked to the microwave reference. A noise model applicable for arbitrary contributions of oscillator phase noise is presented, and a corresponding maximum-likelihood estimator of unknown parameters is also reported. The signal processing is applicable for Lorentzian lineshape under nonsaturating conditions. The estimation is carried out using a convergent iterative algorithm capable of jointly processing the in-phase and out-of-phase data in the presence of phase noise and unknown microwave phase. Cramer-Rao bound analysis and simulation results demonstrate a significant reduction in linewidth estimation error using quadrature detection, for both low and high values of phase noise. EPR spectroscopic data are also reported for illustration. (C) 2010 Elsevier Inc. All rights reserved.