Switched ratiometric lock-in amplifier enabling sub-ppm measurements in a wide frequency range.

Lock-in amplifiers (LIAs) are extensively used to perform high-resolution measurements. Ideally, when using LIAs, it would be possible to measure a minimum signal variation limited by the instrument input equivalent noise at the operating frequency and the chosen filtering bandwidth. Instead, digital LIAs show an unforeseen 1/f noise at the instrument demodulated output, proportional to the signal amplitude that poses a fundamental limit to the minimum detectable signal variation using the lock-in technique.

Note: Differential configurations for the mitigation of slow fluctuations limiting the resolution of digital lock-in amplifiers.

The resolution of digital lock-in amplifiers working with a narrow bandwidth (<100 Hz) is limited by slow fluctuations, which can be two orders of magnitude larger (μV range) than the noise of the input amplifier (tens of nV). In order to tackle this issue, affecting state-of-the-art laboratory instrumentation and here systematically quantified, three differential sensing configurations are presented. They adapt to different setup conditions and are based on manual and automatic tuning of dummy references, allowing a 25-fold resolution improvement for enhanced long-term tracking of impedance sensors.

On-Chip Magnetic Platform for Single-Particle Manipulation with Integrated Electrical Feedback.

Methods for the manipulation of single magnetic particles have become very interesting, in particular for in vitro biological studies. Most of these studies require an external microscope to provide the operator with feedback for controlling the particle motion, thus preventing the use of magnetic particles in high-throughput experiments. In this paper, a simple and compact system with integrated electrical feedback is presented, implementing in the very same device both the manipulation and detection of the transit of single particles.