A Bimodal Low-Power Transceiver Featuring a Ring Oscillator-Based Transmitter and Magnetic Field-Based Receiver for Insertable Smart Pills

This letter presents a novel bimodal, low-power, mm-scale transceiver for insertable smart pills. The proposed power amplifier (PA)-less, 915-MHz uplink transmitter (TX) incorporates an $1.2\times 1.2$ mm² on-chip, nonresonated antenna as part of a current-starved ring oscillator (RO) and directly transmits data by turning the RO on/off. This RO-based uplink TX is implemented in 180-nm CMOS along with a power management unit, which generates all internal reference voltages and supplies from a single battery. The uplink TX achieves a data rate of 33 Mb/s and consumes $210~\mu \text{W}$ , resulting in an energy efficiency of 6.4 pJ/bit. The orientation-insensitive magnetic field-based downlink receiver (RX) is implemented with an external 3-D magnetic sensor, achieves 0.02 kb/s of data rate limited by our measurement setup, and consumes 270 $\mu \text{W}$ . Wireless measurements in saline over 150 cm and prototype of the $3.2\times 13.6\times 2.3$ mm³ insertable pill are presented.