Neuron action potential detection with tunnel diode oscillation circuit

We realized for the first time a neuron action potential detection system with tunnel diode oscillation circuit. A tunnel diode oscillator circuit was realized with very high Q (larger than 800,000), very low power (560 uW) and controllable oscillating frequency. Extra-cellular neuron action potentials were generated using a small electric dipole with appropriate input signal. The action potentials were then detected and amplified and input to the tunnel diode circuit that produced a modulated carrier at 16 MHz/8 MHz. This signal was then detected by an external receiver system via inductive coupling and then demodulated, producing the original action potentials. Given the simplicity of this telemetry system and its low power, it can be integrated into a volume smaller than 1 mm³ by using MEMS resonators. Such a miniaturized bio-implantable telemetry system will be invaluable in reverse engineering the brain circuit.