High Precision 16-bit Readout Gas Sensor Interface in 0.13μm CMOS

A high precision 16-bit readout circuit for gas sensor interface is realized in 0.13μm CMOS technology. The front end signal conditioning circuit comprises a low power resistance-to-time period converter with subthreshold operation of transistors. The time-period proportional to the transducer output is digitized using a counter based frequency-to-digital conversion (FDC) technique. In order to handle the sensor signal with a dynamic range of 160dB, subranging technique is employed to provide feedback to front end circuit interfacing the sensor. While the 3 MSBs of 16-bit word restrict the input frequency to FDC between 1MHz and 10MHz, the 13-bit counter operates on this signal to provide a worst case resolution of 0.4%. The power consumption of the readout circuit is 366μW from a 1.2V supply.