An Integrated Fully Differential Current Amplifier With Frequency Compensation for Inductive Sensor Excitation
Maximilian Scherzer, Mario Auer · IEEE Open Journal of Circuits and Systems · 2025
In this article an integrated fully differential current amplifier is presented. It was designed for inductive sensor excitation, in this case for a fluxgate sensor, however the concept is applicable wherever a low noise and precise current is required. A brief review of some of the basic elements of the circuit is given, followed by the development of a model that takes into account output impedance limitations due to mismatch and stability criteria, an essential consideration in the design of a stable current amplifier for inductive loads. Based on the proposed model, the design and implementation of the current amplifier is outlined, identifying potential difficulties for on-chip integration. The final design was then fabricated using a standard 180nm CMOS technology. Measurement results show that the circuit draws only 2.8 mA from a 3.3V supply voltage and occupies a total area of 0.64 mm2. Special efforts were made to accurately evaluate the output impedance, whereby a value of 436k$\Omega $was recorded. In addition, the current amplifier achieves an output-referred noise current of 2.5$\text {nA}/\sqrt {\text {Hz}}$, resulting in a measured signal-to-noise ratio of more than 105.2 dB for a bandwidth of 512 Hz at an output current of 9$\text {mA}_{\text {p-p}}$.