A 1.8Gb/s 8GHz PSK-UWB Transceiver with Extended PPM/PWM Modulation and Embedded Carrier Spreading

Brain-computer interface (BCI) relies on neural sensing systems capable of supporting high-density data collection. To achieve comprehensive and precise monitoring of brain neural activity, the parallel operation of high-density microelectrode arrays (MEAs), with more than 1,000 recording channels for each array, requires a wireless link with a data rate in excess of Gb/s [1]–[2]. In addition, lowlatency real-time data transmission between the internal and external devices is crucial in the BCI, thus necessitating seamless robust communication between the human brain and the external computer. What's more, low power consumption is required for an implantable transmitter and receiver to ensure that heat dissipation does not cause damage to the tissues. UWB technology is promising for the targeted requirements. To achieve Gb/s transmission with a relaxed symbol rate, hybrid modulation methods that combine several conventional modulations have been proposed recently for IR-UWB transceivers [2]–[6]. However, those architectures substantially add complexity on the receiver. The transmitters in [2] and [6] employ the discrete receiver that requires a high-speed oscilloscope acting as an ADC. A 2Gb/s 16APSK transceiver is presented with good energy efficiency [7], but carrier synchronization needs to be done periodically, where the latency is not suitable for the real-time data transmission. In addition, those modulation methods proposed for pulse-based UWB require amplitude modulation, which is highly vulnerable to noise and interference for high-data-rate wideband communication. Even though the conventional BPSK-based UWB transceiver also achieves a Gb/s data rate [8], a high power consumption of 150mW limits its applications. In this work, we present a 1.8Gb/s PSK-UWB transceiver that achieves real-time data transmission with carrier synchronization, while consuming tens of milliwatt only. Without relying on the amplitude modulation, the transceiver directly modulates the phase of an 8GHz carrier with combined multi-bit PPM and PWM modulations, namely extended PPM/PWM (E-PPWM). To comply with the UWB spectrum mask, the carrier power is further spread with wideband FM. The proposed PSK-UWB transceiver architecture has following features. Firstly, the EPPWM relaxes a symbol rate significantly. Secondly, the phase modulation improves the SNR requirement over amplitude-based modulation. Thirdly, a Costas loop [9]–[10] is employed in the receiver to perform real-time carrier recovery as well as PSK demodulation for real-time data transmission. In addition, the demodulated analog voltage by the Costas loop is converted to digital outputs by a 6b TDC. The E-PPWM PSK signal is modulated and demodulated by simple digital circuits based on a delay line, enabling low power consumption.