Process for filtering an electrical signal by charge transfer into a semiconductor and switch capacitor filter using such a process

A switched capacitor filter using a process for filtering an electrical signal by transferring charges into a semiconductor substrate, which is covered with a first insulating layer on which is arranged a first group of electrodes constituting with the first insulating layer and the substrate charge storage capacitors, whilst a second group of electrodes is interposed with the first and is separated therefrom by a second insulating layer the electrodes of said second group constituting with the first and the second insulating layers and the substrate switches which control the transfer of charges between the storage capacitors, wherein the processing of each sample of the electrical input signal comprises the following stages:

• (a) a quantity of charges corresponding to the sample of the electrical input signal during processing is introduced beneath the first capacitor (C.sub.3) in the charge transfer direction;
• (b) beneath the last capacitor (C.sub.6), in the charge transfer direction, is introduced a quantity of charges which is equal to that already there, during the processing of the preceding sample of the electrical input signal and prior to the beginning of the transfer of charges from said last capacitor to means which convert the charges into an electrical voltage;
• (c) a common surface potential is established between two successive capacitors, whereby during the said stage the capacitors are brought to a constant potential V.sub.g ;
• (d) the charges are transferred from the last capacitor in the charge transfer direction to means which convert the charges into an electrical voltage;
• (e) during the processing of each sample of the electrical input signal, a common surface potential is established between one of the storage capacitors of the charges, ensuring the looping of the filter, and the following capacitor in the charge transfer direction, said capacitors being respectively raised during said stage to voltages V.sub.g +.DELTA.V.sub.S and V.sub.g, in which .DELTA.V.sub.S is the variation of the output voltage of the filter for the preceding sample of the input signal, the order of the stages (a), (b), and (e) of the process being random, but stages (a), (b), and (e) must precede stage (c) which in turn must precede stage (d);
• wherein said filter comprises a diode (D) located in the semiconductor substrate (1) and raised to a constant potential V.sub.D and a grid (G.sub.G) located in the same plane as the storage capacitors (G.sub.3, G.sub.4, G.sub.5, G.sub.6) and raised to a constant potential V.sub.DD which exceeds V.sub.D, which controls the current supplied by the diode, the grid being separated from the first capacitor in the charge transfer direction by a switch I.sub.1 located in the same plane as the other switches (I.sub.5, I.sub.6, I.sub.7) and the first capacitor being connected to the common point of two transistors T.sub.1 and T.sub.2, arranged in series, and respectively connected to the input signal E and to the voltage V.sub.g, transistors T.sub.1 and T.sub.2 and switch I.sub.1 being subject to periodic potentials (.phi..sub.A, .phi..sub.B) such that during stage (a) of the process, transistor T.sub.1 is conductive and switch I.sub.1 is switched off and during stage (c) transistor T.sub.2 conducts.