This paper presents a coin-cell powered small size wireless sensor node with a sensor bridge biased by an energy-efficient DC-DC converter. To reduce the switching noise of the DC-DC converter, a Wheatstone bridge with differentially balanced in wide resistance range is used. Circuit parameters, such as bridge resistances and amplifier offset are automatically set to the optimal values in the startup sequence. Proposed sensor interface achieved power reduction by 57.3% and intermittent operation further reduces the power consumption by 78.6% from which uses LDO. The developed tiny wireless sensor node with a nanoscale gas sensor device successfully demonstrated 100ppm hydrogen gas detection.