An Impulse Radio PWM-Based Wireless Data Acquisition Sensor Interface

A sensor interface circuit based on impulse radio pulse width modulation (IR-PWM) is presented for low power and high throughput wireless data acquisition systems (wDAQ) with extreme size and power constraints. Two triple-slope analog-to-time converters (ATC) convert two analog signals, each up to 5 MHz in bandwidth, into PWM signals, and an IR transmitter with an all-digital power amplifier combines them while preserving the timing information by transmitting impulses at the PWM rising and falling edges. On the receiver side, an RF-LNA followed by an envelope detector recovers the incoming impulses, and a T-fiipflop reverts the impulse sequence back to PWM to be digitized by a time-to-digital converter (TDC). Detailed analysis and design guideline on ATC was introduced, and a proof-ofconcept prototype was fabricated for a capacitive micromachined ultrasound transducer imaging system in a 0.18-mu m HV CMOS process, occupying 0.18 mm(2) active area and consuming 3.94 mW from a 1.8 V supply. The proposed TDC in this prototype yielded 7-bit resolution, while the entire wDAQ achieved 5.8 effective n umber of bits at 2 x 10 MS/s.