The authors present an electronic system fitted in an off-the-shelf programmable system on chip (PSoCtrade) mixed signal array device from Cypress Semiconductors devoted to readout of a capacitive biosensor. The offset voltages of the analog blocks must properly be taken into account in order to obtain a good reproducibility of the performance of different chips and different lots and for accurate measurements in a great range of capacitance values (100 pF - 10 muF).