A sensor interface IC with single-line quasi-digital output for ligament balance measuring system in total knee arthroplasty is presented. This front-end circuit consists of a gain-programmable sample-and-hold stage, a novel voltage-pulses converter and timing control logic. The circuit measures the voltage across resistive bridge sensors and produces a serious of pulses dependent on that voltage, which represents a 16-bit quasi-digital output. The circuit can operate under 1.2V to 3.6V voltage supply for single battery application with 116-160uA power consumption. The measured resolution is 60.1μVpp (1.35g) with ±100mVpp input. The maximum update rate is up to 6.25KSps. The chip has been design and fabricated in 0.18-μm 1P6M CMOS process with active area of 775×500μm2.