A digitally programmable modulation and lock-in set-up

Abstract

A modulation and lock-in set-up has been developed as a modular assembly for measuring systems detecting weak and noisy signals providing a synthesizer voltage or current source in order to modulate the quantity to be measured, and a phase-sensitive detecting (PSD) circuit. The amplitude and the frequency of the modulation source, the phase of the PSD square-wave reference, the PSD gain and its low-pass cut-off frequency are digitally programmable. The prototype set-up covers the frequency range from 0.1 Hz to 999 Hz with a resolution of 0.1 Hz, whereas the phase-set increments of the lock-in part are about 2 degrees .

Low-cost, digital lock-in module with external reference for coating glass transmission/reflection spectrophotometer

“…However, during the past 35 years, it has been increasingly recognized that digital techniques could improve certain aspects of the lock-in performance. Advantages of the digital lock-in have been claimed in the literature [2][3][4][5][6][7][8][9][10][11][12][13][14], such as the extension of the carrier frequency range to arbitrarily low values, extension of the filter time constants to both shorter and longer values, the rejection of unwanted DC and low-frequency signals and reduced drift, among others. Digital lock-ins are not a recent development; they appeared over 30 years ago [2].…”

“…Digital lock-ins are not a recent development; they appeared over 30 years ago [2]. The published literature on digital lock-ins falls into two categories: first, the hardwarebased digital lock-ins that require the construction of specific electronics [5][6][7][8]; second, the software-based versions that are constructed with commercially available boards or instruments connected or not to a personal computer [9][10][11][12][13][14][15]. Of course, there are also commercially available digital lock-ins [16].…”