In vivo testing of a low noise 32-channel wireless neural recording system.

We present a 32-channel wireless implantable neural recording system-on-a-chip (SoC) that operates based on time division multiplexing (TDM) of pulse width modulated (PWM) samples with minimal substrate noise and interference. We have utilized analog-to-time conversion (ATC) on the transmitter and time-to-digital conversion (TDC) on the receiver to reduce the size and power consumption of the implantable unit by moving the digitization circuitry to the external unit. We have managed the TDM switching times such that no switching occurs during sensitive sampling onsets. The chip has been implemented in the AMI 0.5-microm standard CMOS process, occupying 3.3 x 3.0 mm(2) and consuming 5.6 mW at +/-1.5 V when all channels are active. The measured input referred noise for the entire system, including the receiver at 1 m distance, is only 4.9 microV(rms) from 1 Hz approximately 10 kHz. Finally, in vivo testing results on rats have been presented to validate the full functionality of the system.