Low-power, implantable sensing system for signal detection from the central or peripheral nervous system

A low-power, implantable electrode array sensing system for picking up a number of signals from the central or peripheral nervous system is described. The sensed and amplified signals are intended for use in prosthetic limb control or functional electrical stimulation (FES) of paralyzed limbs. The sensing system itself contains deblocking capacitors, low-noise amplifiers (LNA), active filtering and threshold detection logic. Blocking capacitors are used on the array of electrode inputs to meet safety guidelines for electronic devices to be dc-blocked from tissue. Voltage division loss between the dc-blocking capacitors and the parasitic capacitance of the LNA´s large input PFETs is overcome by using positive feedback with a replica parasitic. Programmable filtering with dc-offset correction on the amplifier outputs gives a dc-blocked and yet ultra-low frequency, high-pass filtering with an overall frequency response ranging from 0.035 Hz to 7000 Hz and an input signal range up to 200 mVpp. A 4-channel, 32 input sensing system was designed and fabricated in a 0.5mum CMOS process and occupies an area of 3.24 mm²/channel. It operates at 2.7 V and draws 12muA/channel, providing programmable differential gains between 4 and 1200, and an input referred noise voltage of 5.6 muV_rms over a band of 10 Hz to 7 kHz