A Wirelessly Powered UWB RFID Sensor Tag With Time-Domain Analog-to-Information Interface

This paper presents a wirelessly powered radio frequency identification sensor tag with an analog-to-information interface. A time-domain interface, incorporating an ultra-low-power impulse radio ultra-wideband (IR-UWB) transmitter (TX), is employed. The analog signal from the sensor is compared with a triangular waveform, resulting in a pulse-position modulation signal to trigger UWB pulses. Thanks to the high time-resolution IR-UWB radio, time intervals of the impulses can be used to represent the original input value, which is measured remotely on the reader side by a time-of-arrival estimator. This approach not only eliminates the analog-to-digital converter (ADC) but also significantly reduces the number of bits to be transmitted for power saving. The proposed tag is fabricated in a 0.18-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> CMOS process with an active area of 2.5 mm². The measurement results demonstrate that a 300-kS/s sampling rate with a 6.7-bit effective number of bits (ENOB) is obtained via a UWB receiver with a sensitivity of −93 dBm and an integration window of 10 ns. The ENOB is improved to 7.3 bits when the integration window is reduced to 2 ns. The tag can be powered up by a −18-dBm UHF input signal. The power consumption of the proposed tag is 41.5 <inline-formula> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> yielding a 1.3-pJ/conv.step figure of merit, offering 9<inline-formula> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> and 67<inline-formula> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> improvements compared with the state of the art based on an ADC and a backscattering TX, and the tag based on an ADC and a narrowband TX, respectively.