A CMOS MedRadio Transceiver With Supply-Modulated Power Saving Technique for an Implantable Brain–Machine Interface System

Abstract

A MedRadio 413–419-MHz inductorless transceiver (TRX) for an implantable brain–machine interface (BMI) in a 180 nm-CMOS process is presented. Occupying 5.29 mm2 of die area (including pad ring), this on–off keying (OOK) TRX employs a non-coherent direct-detection receiver (RX), which exhibits a measured in-band noise figure (NF) of 4.9 dB and $S_{11}$ of −13.5 dB. An event-driven supply modulation (EDSM) technique is introduced to dramatically lower the RX power consumption. Incorporating an adaptive feedback loop, this RX consumes 42-/92- $\mu \text{W}$ power from 1.8-V supply at 1/10-kbps data rates, achieving −79/−74-dBm sensitivities for 0.1% bit error rate (BER). The TX employs a current starved ring oscillator with an automatic frequency calibration loop, covering 9% supply voltage variation and 15 °C–78 °C temperature range that guarantees operation within the emission mask. The direct-modulation TX achieves 14% efficiency for a random OOK data sequence at −4-dBm output power. Wireless testing over a 350-cm distance accounting for bio-signal data transfer, multi-user coexistence, and in vitro phantom measurement results is demonstrated.