Subminiature Apparatus for Radio-Telemetering of EEG Data

The use of radio-telemetering has several advantages for the recording of EEG data from unrestrained subjects. By use of transistor techniques, miniaturization of the apparatus carried by the subject is made possible. Design considerations for a transistorized high input impedance, low-noise, single-sided amplifier for the EEG frequency and dynamic range are evaluated. Common-collector configuration and an unconventional input circuit of the first stage, and careful choice of transistors and their operating points, enable one to obtain satisfactory noise performance in the actual amplifier. A differential-input amplifier, based on features utilized in the design of a single-sided type, was developed. Rejection of in-phase signals (better than 3000 to 1 at 50 cps), an input impedance of 300 kilohms, and low noise referred to the input (3¿v peak-to-peak at 20 kilohms of interelectrode resistance), determine the main features for EEG amplification purposes. A VHF FM one-stage oscillator, working at 30 Mc, provides transmission of signals up to a distance of 10 m. EEG records taken from subjects free in behavior, and even during convulsions, show no artifacts.