Device for reading a quantity of electric charges and charge-filter equipped with said device

A device for reading a quantity of electric charges arriving at a point B. Two MOS transistors Q2 and Q3 are connected in series and with one terminal to point B. A capacitor CA is connected to a common point A of the two transistors. A transistor control circuit charges the capacitor CA from a low potential VDD. The capacitor CA and the transistors Q2 and Q3 maintain a constant potential at the point B at the time of charge inflow. This results is a variation of potential at the common point A in accordance with the incoming charges at B. Thus, the variations of potential at point A is a measure of the charges arriving at point B.