A novel conditioning circuit for low frequency signals is presented in this paper. The first stage consists of the input stage of a conventional instrumentation amplifier employing chopper amplifiers, in order to provide high input impedance and low flicker-noise. A fully-differential voltage-to-current converter eliminates the common-mode input signal, thus leading to high CMRR, and provides two symmetrical output currents to charge and discharge a capacitor as part of a current-to-frequency converter. In this way, a quasi-digital output is obtained. Simulation results in a 0.35μm CMOS process biased with a 2V single-supply voltage are presented. The circuit shows an overall sensitivity of 7MHz/V with a linearity error lower than 1.2% and total power consumption of 3.2mW.