Development of a Seven Channel Telemetry Transmitter

Abstract

Study of electroencephalograms (EEG) under normal behavior conditions required the development of a small, reliable telemetry system. Here two hybrid ceramic packages were attached face to face to provide a hermetically sealed seven channel telemetry transmitter with glass to metal seals around the seven differential pairs of input leads and the power supply leads. The transmitter's antenna is enclosed in the package by using two loops of gold substrate etched in a pattern around the other circuitry. The package measures .8 x 2.2 x 2.4 cm and weighs 8.5 gms. Input noise level is below 1 microvolt (rms) and dynamic range is from 1 to 250 microvolts (rms) with a frequency response (6 dB down) of 1 Hz to 150 Hz. Power requirements are 2.1 to 3.6 ma at 2.0 and 3.3 vdc., respectively, with at least 80% (3.3 and 9.5 mw, respectively) going to the radio frequency stage. Data are time multiplexed for pulse position modulation of an 88 to 108 MHz carrier. Maximum measured range of transmission with a 3 volt battery has been 10 m in air. This transmitter is well suited for the study of any animal large enough to carry the package and a battery. Other biopotentials such as EMG and ECG can be telemetered by increasing multiplexor rates and/or attenuating input signal levels.