Theocharous E
Quality of Life Division, National Physical Laboratory, Teddington, TW11 0LW, UK.
Appl Opt. 2008 Mar 10;47(8):1090-6. doi: 10.1364/ao.47.001090.
In applications where low signal-to-noise ratios are encountered, the use of phase-sensitive detection (PSD) is highly advantageous and is applied widely. However, the characteristics of lock-in amplifiers that utilize the PSD technique, such as the linearity of the output and the gain of these instruments, have not been extensively evaluated. The author proposes a method for measuring the linearity characteristics of lock-in amplifiers and describes how this method was used to measure the linearity factor of three nominally identical commercially available digital lock-in amplifiers. The results of this study show that the linearity factor of these lock-in amplifiers can deviate from unity by more than 0.1% over a factor of 2 change in output. Moreover, the linearity characteristics of these lock-in amplifiers vary from one instrument to the next. The linearity characteristics were shown to be independent of the reference frequency, the time constant, and the temporal profile of the signal being analyzed. However, they were found to be dependent on the sensitivity settings of these instruments. The linearity characteristics of these instruments were observed not to change with time. This implies that, where the uncertainty contribution due to the nonlinearity of a lock-in amplifier is significant, the nonlinearity can be evaluated by using the method described in this article and can be used to apply corrections.
在遇到低信噪比的应用中，使用相敏检测（PSD）非常有利且应用广泛。然而，利用PSD技术的锁定放大器的特性，如输出的线性度和这些仪器的增益，尚未得到广泛评估。作者提出了一种测量锁定放大器线性特性的方法，并描述了如何使用该方法测量三款标称相同的市售数字锁定放大器的线性因子。本研究结果表明，这些锁定放大器的线性因子在输出变化2倍的范围内可能偏离单位值超过0.1%。此外，这些锁定放大器的线性特性因仪器而异。结果表明，线性特性与参考频率、时间常数以及被分析信号的时间轮廓无关。然而，发现它们取决于这些仪器的灵敏度设置。观察到这些仪器的线性特性不会随时间变化。这意味着，在锁定放大器非线性引起的不确定度贡献显著的情况下，可以使用本文所述方法评估非线性，并可用于进行校正。
