Regenerative current amplifier using van der Pol approximation

When van der Pol oscillator linear damping parameter is positive then this oscillator becomes a nonlinear resonant amplifier of high sensitivity for small ac signals with the frequencies located in the vicinity of the oscillator natural frequency. The gain characteristic of this amplifier is similar to the gain characteristic of logarithmic amplifier; the sensitivity is high for small signals and, due to the nonlinear damping parameter, is reduced for the signals of higher amplitudes. Application of this amplifier in regenerative receiver requires a precise control of the linear term, i.e. the Q-factor of linear low-level signal operation. The proposed amplifier is realized using a modified active inductor circuit with compensation of resistive component in input admittance; this approach provides the required high value and good control of Q-factor. The simulations of amplifier selectivity characteristics are given for the design example using 130 nm CMOS technology.