An Ultra-Compact and Fully Integrated Tunable IR-UWB Transmitter in 28-nm CMOS for High-Density Neural Implants

This paper presents a fully-CMOS, tunable impulse radio ultra-wideband (IR-UWB) transmitter for high-density implantable neural recording systems. Fabricated in 28 nm CMOS technology, the transmitter features an ultra-compact edge-combining architecture based on a digitally tunable impulse response filter (IRF) occupying only 0.0027 mm² . The measured output exhibits a central frequency of 4.5 GHz with a 10-dB bandwidth of 3.6 GHz, providing robust spectral performance. It achieves 1 GHz frequency tunability by adjusting pulse widths from 650 ps to 800 ps, ensuring compliance with FCC spectral masks. A current-starved ring VCO (CSRVCO), with a compact 150 µm² layout, serves as the clock source, offering wide frequency tuning, low power consumption, and enhanced output power. The transmitter employs On-Off Keying (OOK) modulation and delivers a peak output amplitude of 660 mV with up to 5.1% energy efficiency. At a 20 MHz pulse repetition rate, the transmitter consumes only 78 µW while producing -24.5 dBm of output power. Measurement results confirm compliance with FCC regulations and suitability for deep implantation in biomedical applications. The design achieves a competitive Figure-of-Merit (FoM) of 0.017 (mm² · pJ)/(b · V), demonstrating its scalability and efficiency compared to prior state-of-the-art solutions.