Fifteen-Electrode Time-MAultiplex EEG Telemetry from Ambulatory Patients

A 15-electrode time-multiplex EEG telemetry unit is described that fits on the patient's head. A continuous 24-hour transmission is possible. RF-to-AF feedback is prevented by mode switching at the basic cycle rate, 400 Hz, so that the RF transmission is cut off while the AF amplifiers are on, and vice versa. The channel rate is 12,800 Hz. The channel 16 input consists of a 200-Hz reference signal. The unit weighs 200 grams, and draws 10 mA at 5 V. Each channel bandwidth extends from 0.36 to 59 Hz. The output is FM with a peak deviation of 75 kHz of a 20 MHz carrier. The decoder locks on a 400 Hz AM sync signal. RF carrier shift due to motion artifact is fed back to the 15 data channels so as to cancel out their shift components.