The calibration of the transresistance gain of low-current dc amplifiers can be performed with the capacitance-charging method, where the calibration current is generated by a calibrated voltage ramp applied to a reference capacitor. The method is typically implemented with a purposely-built voltage source having a very low-frequency trapezoidal pe- riodic waveform output. Here we propose a variation of the method based on a sinusoidal excitation, that can be pro- vided by a commercial oscillator and therefore more easily implemented. Sampled sinusoidal input and output are pro- cessed with a seven-parameter sine-fitting algorithm. The comparison between calibration with sinusoidal and trape- zoidal excitations is ongoing and will be presented at the Conference.