EEG Biopotential Ampifier

This project was the end of semester project for a class called Biopotential Amplifiers and Implantable Devices taught by Dr. Jonathan Viventi. The project was, of course, a biopotential amplifier – specifically an amp for EEG signals. I used LTSpice for circuit simulation and the open source Circuit Maker for PCB design.

Design Criteria

  • Two input electrode channels, one reference channel, and one right leg drive channel.
  • 0.1-50 Hz bandwidth
  • < 2µV RMS noise in the passband
  • 500µV-pp input voltage range
  • +/- 300mV input offset tolerance
  • < 5mA power consumption
  • Distortion under 1%
  • Leakage current < 1%
  • Battery powered
  • Cost under $50

For the purposes of this project, I was limited to a choice of two op-amps (the OPA347PA and the MCP6242-E/P) and only one choice of differential amp (INA2126PA).

Design

EEG recordings typically fall in the range of the low hundreds of microvolts, so for gain I was limited by the voltage output of my battery. The CR123A battery outputs 3V, but falls to roughly 2.2V output after extended use. To compensate for decreasing voltage output and to prevent saturation, I wanted to limit my output to +/- 500mV peak to peak, so I chose a gain of roughly 2400x (68dB).