Ultra-stable, low-noise two-stage current source concept for electronics and laser applications

This study presents a two-stage current source concept which features low-current noise, excellent drift and stability for higher operating currents. Generally, it is much easier to obtain higher stability and lower-noise parameters for small operating currents rather than large ones. This fact was used within this concept, where a precise low-current source (the second stage) corrects the fluctuations of high-current one (the first stage). In details the theory of operation for setup, the noise-sources analysis and measurement results are presented. For a maximum operating current equals 1A, the current noise density of 126nA/Hz (at f=1kHz), long-term stability of +/- 2.1ppm and temperature coefficient equal 2.8ppm/degrees C, were obtained, whereas the current noise below 1nA/Hz was obtained for lower operating currents. Presented circuit is inexpensive to construct, non-thermally stabilised and very small size (1x1.2in(2)). The obtained parameters are competitive to commercial current drivers designed for laser applications. The two-stage current source has been successfully implemented in a fully integrated diode-pumped solid-state lasers.