A 1.8Gb/s, 2.3pJ/bit, Crystal-Less IR-UWB Transmitter for Neural Implants.

Frontier research in neuroscience places a high demand for high-density, implantable, wireless Brain-Machine Interfaces (BMIs) consisting of more than 1,000 recording channels with a sampling rate up to 20 to 30kS/s per channel to acquire the precise activity of a single neuron. A wireless data link with Gb/s throughput is strongly required. In addition to the data-rate, the wireless telemetry module faces a strictly limited power budget of only a few milliwatts, to avoid tissue heating. Thirdly, a compact implant design with as few as possible off-chip components is expected to minimize the harm caused by the implant. Impulse-radio Ultra-WideBand (IR-UWB) enables Gb/s throughput with low power consumption and high integrability, due to its large available bandwidth and circuit optimization. One of the major design challenges of IR-UWB is that the transmit power density is limited to -41.3dBm/MHz to comply with the FCC spectral mask, while the energy per TX pulse needs to be high enough to ensure the transcutaneous data transmission. To alleviate this contradiction, modulation schemes with higher modulation order have been proposed [1–3]. [2] proposed Extended Multi-Pulse-Position Modulation (E-MPPM), achieving a modulation order of 3. However, the sync pulse in E-MPPM reduced the modulation order by 1/3. [3] improved the modulation order to 7 by introducing a 4PAM-8PSK-4PPM hybrid modulation, but it requires an initiative reduction of the TX pulse amplitude due to the use of PAM, resulting in a reduction of the transmission range. In addition, the 8PSK modulation used in [3] requires a high frequency 8-phase carrier with a power-hungry upconversion architecture. On the other hand, an all-digital transmitter with edge-combine technique features higher power efficiency [1], [2], [4], but the modulation order is limited to 1 to 3 due to the lack of phase modulation.