A reconfigurable time-domain comparator for multi-sensing applications

Wireless sensor network applications typically include various sensors (temperature, humidity, gas, etc.) and each sensor has different requirements of speed, noise, offset, and power consumption. In order to optimize the performance and allow long-time operation, reconfigurability is mostly desirable in the readout circuitry. In this paper, a reconfigurable time-domain comparator (RTDC) with low noise and low offset is proposed, mainly for reconfigurable SAR ADCs in wireless sensor nodes. With a supply voltage of 1.8 V, it can be dynamically reconfigured to operate in seven different modes for different sensing scenarios. From Mode 1 to Mode 7, the maximum operating speed of the comparator ranges from 182 MHz to 20 MHz with its input referred noise been reduced exponentially from 142 μV to 63.4 μV and its offset been reduced exponentially from 7.64 mV to 2.55 mV, respectively. The simulated energy efficiency is 1.27 pJ/conv in Mode 1 and it linearly increases to 9.48 pJ/conv in Mode 7. This wide operating range enables the best possible trade-off for the sensing node application at hand.