MYOELECTRIC ELECTRODE AMPLIFIERS: REJECTION OF UNWANTED COMMON MODE SIGNALS

This investigation was prompted by a chance observation during trials of the ToMPAW arm system [1]. The arm has a carbon fibre structure which, although not directly connected to the system electronics, can act as an antenna for electromagnetic interference. The user suspected that better control was obtained when the structure was grounded by touching it. A more permanent solution was tried by adding a conductive plastic patch to the inside of the socket, providing a safe high resistance ground path without discomfort (Figure 1). The user reported a subjective improvement with this modification. Myoelectrode amplifiers are designed with a high common mode rejection ratio (CMRR) and good d.c. isolation, and externally applied signals would be expected to have little influence, so further investigation was warranted.