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 1 A, the current noise density of 126 nA/√Hz (at f = 1 kHz), long-term stability of ±2.1 ppm and temperature coefficient equal 2.8 ppm/°C, were obtained, whereas the current noise below 1 nA/√Hz was obtained for lower operating currents. Presented circuit is inexpensive to construct, non-thermally stabilised and very small size (1 × 1.2 in2). 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.