An analog core computing the center of pressure in a knee replacement prosthesis

Predicting the lifespan of a knee prosthesis can be done by computing the force distribution, represented by the center of pressure (COP), onto the tibial part of the implant. The COP can be computed in-vivo by means of a telemetry system. The feasibility of such a telemetry system has been shown using a digital computing core. Both the complexity and the power consumption can be reduced using an analog computing core to compute the COP. The core is 10 times smaller than its digital counterpart and one oscillator is removed. Furthermore, only the value of the computed COP needs to be converted into digital. These result in a reduced power consumption of 5.5 percent. The current-mode computing core has been designed and simulated for a 0.35μm CMOS process.