Abstract
Recently there are evidences to show that the over-active neural behavior in specific brain area may cause the syndrome of Parkinson’s disease. Continuous neural signal recording and proper electric stimulation has been clinical proven to be a possible tool to alleviate the oscillation then calm down the tremble. In order to capture extremely low frequency neural signals, the DC block capacitor added in front of the sensor would often be with nano-farad scale. This work uses the complementary leakage-balanced structure to form an ultra-high-resistance pseudo resistor for 0.1Hz highpass corner frequency with 60pF input capacitance. For in vivo measurement, recording system always suffer from motion artifact interference and high voltage damage caused by stimulator. The former will be large to saturate amplifier output ; the latter may break the thin gate oxide of input MOS. To overcome this problem, we develop a motion artifact fast recovery loop with the recovery time of 200μs. The PMOS diodes associated with input stage provide dual discharge paths, which can effectively reduce the high voltage damage caused by stimulator. By using low noise circuit design skills, input equivalent noise from 0.1Hz to 5kHz down to 4.04μV, and the NEF is 3.8. Thanks for rail-to-rail opamps insertion and smart arrangement for the position of switches in VGA, the THD is 0.086% even if the differential output swing reaching 1V. At output, a high bandwidth and slew rate analog buffer is added to program the LFP or spike mode for neural signal recording.