Design of a Low-Power, High-Data-Rate, and Crystal-Less All-Digital IR-UWB Transmitter for High-Density Neural Implants

This article presents an all-digital, crystal-less impulse radio ultra-wideband (IR-UWB) transmitter for the high-density neural implants with several thousand channels. A six-order hybrid modulation scheme combining the differential 16-pulse-position modulation (D16PPM), pulsewidth modulation (PWM), and differential bi-phase shift keying (DBPSK) is proposed to achieve a high data rate and guarantee the transcutaneous data transmission. A detailed theoretical analysis of the signal-to-noise ratio (SNR) and symbol error rate (SER) relationship is included, along with the analysis of removing the crystal. The proposed transmitter uses a 42-stage bi-phase ring oscillator (RO) to provide all the edges to combine. A highly symmetrical pulse generator and a pulse shaper (PS) with an edge detector (ED) chain are designed, respectively, to realize the proposed modulation scheme efficiently. The transmitter achieves a data rate of 1.8 Gbps with a power consumption of only 4.09 mW. Thus, a power efficiency of 2.3 pJ/bit is achieved. In an ex vivo test, a transcutaneous transmission range of 20 cm was measured with 18-mm pork tissue applied.