A 15-Electrode Totally Implanted Time-Multiplex Telemetry Unit

A 15-electrode totally implanted time-multiplex telemetry unit is described that is powered by two mercury cells in series. Transcutaneous radio frequency (RF) turn-on and magnetic turnoff are used to conserve battery power. The basic cycle rate is 400 Hz, channel rate 6400 Hz. The channel 16 input consists of a 200-Hz 5 mV peak-to-peak (p-p) reference signal, and a 3200-Hz sync signal is added to all channels. The unit is
1.5 \times 2.5 \times 8
cm in size, weighs 41 g, and draws 3.5 mA. Low-frequency cutoff is at 0.2 Hz. The output is FM with a peak deviation of 75 kHz of a 20 MHz carrier at 5 mV peak channel input. The equivalent noise input is 2.8 μV root mean square (rms). The decoder automatically locks on the reference signal square wave with the aid of an exclusive-OR gate.