Biomedical Amplifiers Design Based on Pseudo-Resistors: A Review

The demand for efficient, robust, and cost-effective brain–machine interface (BMI) systems continues to increase in the last decade. One of the fundamental design blocks in such systems is the signal amplification and filtering. Generally, biomedical signals are characterized by low amplitude and low frequency in a noisy environment. Therefore, they need to be amplified and filtered before passing the signal to the next processing stage. In this review article, a comprehensive survey is conducted in existing literature of two-stage biomedical amplifiers, focusing on the impact of the pseudo-resistor non-linearity on the system’s performance. First, the common categories of pseudo-resistors are presented and discussed. Then, different amplifier designs, targeted for biomedical applications, are identified and studied considering the influence of the pseudo-resistors on the performance. A special focus was given to the impact of the process, voltage, and temperature (PVT) variations where experiments are conducted to test the performance under different variation tests. Different two-stage biomedical amplifiers, used in bio-detection systems, with programmable gain and bandwidth (BW) features based on pseudo-resistors are implemented. The designs are realized and simulated using LTspice utilizing 90 nm process technology, BSIM4, version 4.3, level 54.