11.6 A multi-channel neural-recording amplifier system with 90dB CMRR employing CMOS-inverter-based OTAs with CMFB through supply rails in 65nm CMOS

• Published in: 2015 IEEE International Solid State Circuits Conference (ISSCC) pp. 1 - 3
• Main Authors: Ng, Kian Ann, Xu, Yong Ping
• Format: Conference Proceeding Journal Article
• Language: English
• Published: IEEE 01.02.2015
• Subjects: Amplification; Amplifiers; Channels; CMOS; CMOS integrated circuits; Feedback; Impedance; Manganese; Noise; Rails; Recording; Rejection; Transistors
• ISBN: 1479962236; 9781479962235
• ISSN: 0193-6530; 2376-8606
• DOI: 10.1109/ISSCC.2015.7062998

In addition to minimizing input-referred noise and lowering power consumption, a good multi-channel neural amplifier system should be able to significantly reject common-mode electrical interference (CMI). The dominant source of CMI comes from capacitive coupling of electrical mains supply line or EMGs onto neural tissues and can be as high as 100mV pp . Thus any neural recording setup needs a total common-mode rejection ratio (TCMRR) of at least 70dB for a minimum detectable neural signal of 5uV rms . However, multi-channel neural amplifiers are commonly implemented with a shared reference input whose input impedance is several times lower than that of corresponding signal inputs. This results in a large mismatch at the bipolar electrode-amplifier input interface. As analysed in Fig. 11.6.1, the TCMRR is significantly degraded below 70dB, independent of an amplifier's intrinsic CMRR (ICMRR). In this work, we report a micro-power, low-noise 16-channel neural amplifier that eliminates this impedance mismatch problem by using single-ended CMOS inverter-based LNAs for both the reference and signal inputs. Compared to conventional replica channel works, when operating at 1V supply, the LNAs can accommodate a large input CMI of up to 220mV pp through the use of a common-mode feedback (CMFB) loop implemented through the supply rails of the CMOS-inverter-based LNAs, which coincidentally leads to a high amplifier ICMRR.