A 16-Channel Neural Recorder with 2.8 nJ/bit, 971.4 kbps sub-2.4 GHz polar transmitter

This paper proposed a miniature neural interface system. A single chip neural recording SoC was fabricated in 40nm CMOS process with an area of 3mm×3mm. It integrated a 16-channel analog front end (AFE), and a low power constant envelope polar transmitter. The general form of continuous phase modulation was used as the modulation scheme. Algorithms for receiver including frequency offset calibration, frame synchronization, and symbol demodulation were proposed and implemented on a software-defined radio platform. Simulation results showed that a bit error rate of $10^{-4}$ is achieved at the signal to noise ratio of 19 dB at high data rate mode of 971.4 kbps. A graphic user interface was designed for channel decoding and real-time display. Experimental results showed that the input referred noise of the AFE is 2.87$\mu V_{rms}$, and the energy efficiency of the transmitter is 2. 8nJ/bit. The proposed chip consumes 5. 47mW power in total in its maximum workload. The neural signal can be correctly decoded at least at a RSSI (Received Signal Strength Indicator) of -95dBm, and a working distance of 8 m. In-vivo tests on rat have been conducted, showing a good usability of the proposed system.