A wirelessly ultra-low-power system for equilibrium measurements in total hip replacement surgery

This paper presents a wirelessly ultra-low-power system for equilibrium measurement in Total Hip Replacement (THR) surgery. The system consists two parts: the Contact Array Measurement System (CAMS) and the display part. The CAMS is designed to measure the contact distribution of the sensors array between the surface of the femoral head and the acetabulum of the template. The sensors array is designed on the surface of the femoral head and the data is transmitted wirelessly by a low power transceiver. The CAMS composes of a sensors array (31 sensors used in current system), an ultra-low-power microprocessor, and an ultra-low-power transceiver. The display part demonstrates the contact distribution in-vivo in 3D images. The two parts of the system communicate with each other on a RF link at the band of 400MHz. The signal conditioning circuits, the sub-threshold 8-bit microprocessor and the transceiver have been designed and fabricated in 0.18μm CMOS process. The tested results show that the solution of the signal conditioning circuits is 60.1μV_pp (1.35g) with ±100mV_pp input and the chip can operate under 1.2V to 3.6V voltage supply for single battery application with 116-160μA power consumption. The 3Mbps MSK transmitter consumes only 3.9mW in total. The system has been validated by experimental results. Some clinical experiments will be carried out in the future.