Universal Programmable DC Amplifier for Low Frequency Noise Measurements

The article describes the functional and circuit implementation of a universal low-noise DC amplifier designed to measure low-frequency noise in complex multi-channel measurement systems. The main advantage of the amplifier is the possibility of external remote control using the popular RS-485 interface, as well as the ability to use built-in zero offset correction algorithms and automatic drift compensation, while maintaining high performance characteristics. A built-in microcontroller with an efficient protocol and a command line interface allows the amplifier to be used as a separate unit, or as an element of the measuring channel with a cascade connection of blocks with the combination of functions. This paper presents the experimental setup for measuring and analyzing the noise of digital potentiometers, which are the main adjusting elements of the amplifier. It is shown that the noise of these electronic components slightly exceeds the noise of resistors with similar values of resistance. Automatic gain control using a MCU unit eliminates the problem of possible over-current digital potentiometer with a large dynamic range of input signal. Using the built-in filter on switchable capacitors controlled by a MCU unit allows you to effectively limit the bandwidth of the measuring path. The voltage gain of the developed prototype amplifier has a range K
_u
= 5 ÷ 100, the equivalent noise level at 1kHz does not exceed 1.14·10
^-9
nV/√Hz.