A sensor circuit is coupled to a sensing element for determining a property, such as a dielectric constant, of a fuel. The circuit includes an excitation voltage signal generator, a synchronization trigger and a processing circuit configured to generate an output signal indicative of the fuel property. The excitation signal is applied to the sensing element to produce an induced current signal. The synchronization trigger generates a trigger signal when the excitation signal crosses zero volts, at which time the real (resistive) component of the induced current signal is zero. The induced signal is therefore wholly representative of the imaginary component attributable to a capacitance of the fuel, which in turn is dependent on the dielectric constant (and thus ethanol concentration) of the fuel blend. The processing circuit is configured to sample the induced signal in response to the trigger signal and produce the output signal.