A Wide-Band Digital Lock-In Amplifier and Its Application in Microfluidic Impedance Measurement

Abstract

In this work, we report on the design of a wide-band digital lock-in amplifier (DLIA) of up to 65 MHz and its application for electrical impedance measurements in microfluidic devices. The DLIA is comprised of several dedicated technologies. First, it features a fully differential analog circuit, which includes a preamplifier with a low input noise of 4.4 nV/√Hz, a programmable-gain amplifier with a gain of 52 dB, and an anti-aliasing, fully differential low-pass filter with −76 dB stop-band attenuation. Second, the DLIA has an all-digital phase lock loop, which features a phase deviation of less than 0.02° throughout the frequency range. The phase lock loop utilizes an equally accurate period-frequency measurement, with a sub-ppm precision of frequency detection. Third, a modified clock link is implemented in the DLIA to improve the signal-to-noise ratio of the analog-to-digital converter affected by clock jitter of up to 20 dBc. A series of measurements were performed to characterize the DLIA, and the results showed an accurate performance. Additionally, impedance measurements of standard-size microparticles were performed by frequency sweep from 300 kHz to 30 MHz, using the DLIA in a microfluidic device. Different diameters of microparticle could be accurately distinguished according to the relative impedance at 2.5 MHz. The results confirm the promising applications of the DLIA in microfluidic electrical impedance measurements.

Recent Advances in Electrical Impedance Sensing Technology for Single-Cell Analysis

“…Notably, the frequency range of this system is only up to 100 kHz, and its accuracy is lower than that of benchtop instruments. Huang et al developed a wide-band digital lock-in amplifier (DLIA), which features a low input noise of 4.4 , 120 dB dynamic reserve and a phase deviation of less than 0.02° through the whole frequency range up to 65 MHz [ 106 ]. This portable EIS system has been demonstrated by impedance measurements of three sets of micro beads with different diameters.…”

Signal-to-Noise Ratio Analysis for the Voltage-Mode Read-Out of Quartz Tuning Forks in QEPAS Applications

“…QEPAS requires synchronous detection techniques based on lock-in amplifiers (LIAs) to efficiently extract the useful signal component from the noise floor [ 2 , 22 , 23 , 24 , 25 , 26 ]. In LIAs, the amplifier signal is first multiplied with both a sinewave and a 90° phase-shifted copy of that sinewave at a selected operating frequency (f op ); then, a low-pass filter (LPF) is used to retrieve the signal component at f op or its multiples [ 22 , 26 ].…”

Square wave reference digital lock-in detection using non-orthogonal demodulation

“…Digital lock-in detection technique has been widely used in a variety of fields to measure weak signals [ [1] , [2] , [3] , [4] ]. It can measure a signal of interest frequency without being disturbed by noise of other frequencies.…”