Abstract: A new method of modulating and demodulating signals and circuitry therefor is disclosed. The modulation circuit defines a non-linear voltage current transfer function wherein at low voltage levels the current voltage transfer function is substantially linear and at higher voltages, the transfer function is substantially exponential. The modulation circuit can be designed of three parallel branches, a resistive branch, and two diodes in the remaining branches, the anode of one diode being coupled to the cathode of the other diode. Demodulation circuitry is also disclosed that includes a circuit for determining the instantaneous phase and amplitude and then processing circuitry to decode the modulation information based upon the sampled phase and amplitude data.