An Improved Pseudo-Resistor with Well-Biased Technique and Proportional Calibration Technique for Neural Amplifiers

Pseudo-resistors are widely used in neural amplifiers to generate a very low cut-off frequency and avoid DC offset while recording neural signals. However, conventional pseudo-resistors suffer from process variation, temperature variation and body leakage problems, leading to neural amplifier saturation and even instability. To solve these problems, an improved pseudo-resistor is designed with a well-biased technique to minimize the body leakage current and with the proportional calibration technique to achieve process and temperature robustness. The improved pseudo-resistor could achieve a $208.997 \mathrm{G} \Omega$ at 1000 Hz with 8.3% process variation and with mean crossed voltage(caused by body leakage current) 19.1 mV with 0.97% process variation within three standard deviations. The improved pseudo-resistor’s resistance varies by 3.4% and crossed voltage varies by 10 mV with the temperature from $0^{\circ} \mathrm{C}$ to $100^{\circ} \mathrm{C}$. As proof of concept, a capacitively coupled neural amplifier with this improved pseudo-resistor is also designed for testing. This work is designed using a 65 nm process.