With advances in CMOS technology, there has been a significant progress in implementing multichannel implantable neural systems. However, long-term monitoring of the brain activities remains a challenge due to stringent constraints in power, noise and area for hardware implementation. To establish the reliable monitoring of vulnerable neural signals, front-end preamplifier have been explored. Most such amplifiers utilize closed-loop topologies with input transistors but these amplifiers impose the stability constraint, limiting their power-noise efficiency. While low-power open-loop amplifier has been proposed, single-ended output is susceptible to common mode noise and supply fluctuation.
University of Michigan researchers have developed an energy efficient pseudo open-loop amplifier with programmable band-pass filter developed for neural interface systems. The proposed amplifier consumes 400nA at 2.5V power supply, with measured thermal noise level of 85nV/√Hz and input-referred noise of 1.69 microVrms from 0.3Hz to 1 kHz. The amplifier has a noise efficiency factor of 2.43, the lowest in the differential topologies reported up to date to our knowledge. By programming the switched-capacitor frequency and bias current, we could control the bandwidth of the preamplifier from 138 mHz to 2.2 kHz to meet various application requirements. The entire preamplifier including band-pass filters has been realized in a small area of 0.043mm2 using a 0.25µm CMOS technology.
Applications and Advantages
- Amplifier for neural interface systems
- Retention of high linearity and stable operation over process and bias variations
- Reduced area