Ultra-low noise and high bandwidth bipolar current driver for precise magnetic field control.

Current sources with extremely low noise are significant for many branches of scientific research, such as experiments of ultra-cold atoms, superconducting quantum computing, and precision measurements. Here we construct and characterize an analog-controlled bipolar current source with high bandwidth and ultra-low noise. A precise and stable resistor is connected in series with the output for current sensing. After being amplified with an instrumentation amplifier, the current sensing signal is compared with an ultra-low noise reference, and proportional-integral (PI) calculations are performed via a zero-drift low-noise operational amplifier. The result of the PI calculation is sent to the output power operational amplifier for closed-loop control of the output current. In this way, a current of up to 16 A can be sourced to or sunk from a load with a compliance voltage of greater than ±12 V. The broadband current noise of our bipolar current source is about 0.5 μA/Hz and 1/f corner frequency is less than 1 Hz. Applications of this current source in a cold atom interferometer, as well as active compensation of a stray magnetic field, are presented. A method for measuring high-frequency current noise in a 10 A DC current with a sensitivity down to a level of 10 μA is also described.