A Receiver for Inductive Ear-to-Ear Communication

Abstract

This paper proposes a receiver circuit for inductive ear-to-ear communication. Its input resonance structure, an LCR front-end, is optimized for both a data transmission rate of 100 kbit/s and maximum voltage excess. Following an analytical study, the optimal quality factor $Q_{\text {LCR}}$ is found to be 12.8. Subsequent amplification of ON-OFF keyed bits is performed with a four-stage JFET amplifier, introducing a total amplification of 68.6 dB at a sensitivity of $31.6~\mu \text{V}$ . Each stage is implemented in common-source JFET topology containing a current source in its drain path instead of the conventional drain resistor. This modification allows for a per-stage increase in voltage amplification by a factor of 1.87, avoiding extra quiescent current (detailed circuit theory is added). A hardware realization for signal demodulation reconstructs the baseband signal. In combination with a dedicated transmitter, a Hartley Oscillator, the inductive ear-to-ear transmission system demonstrates a reliable functionality over a distance of 18 cm. Operation is possible with a standard 1.5 V battery cell requiring low currents on a discrete benchtop prototype [transmitter: 0.8 mA; receiver: 4.0 mA]. Applying a carrier frequency of 3.175 MHz, the system is fully compliant with ITU regulation 5.115.