Feedback circuit for a semiconductor active element sensor

Claim 1

A semiconductor sensor comprising: a main FET having a channel responsive to a change in physical quantity to be detected, wherein said physical quantity is a quantity representing mechanical variation; impedance means which is connected in series with said main FET to form the load thereof; negative feedback means for negatively feeding back the change in potential at a connection point where said main FET is coupled to said impedance means to the gate of said main FET; and an output terminal for receiving an output signal based upon said potential change fed from said negative feedback means, wherein said main FET is an insulated-gate FET and said negative feedback means includes first amplifying means having a voltage amplification factor larger than unity, said output signal being obtained by amplifying said potential change, further wherein said load is an insulated-gate FET having a conductivity type which is different from that of said main FET, and further wherein said insulated-gate FET constituting said main FET and said insulated-gate FET constituting said load are coupled to have their source and drains connected in series with one another between first and second predetermined potentials, and wherein said first amplifying means is coupled to feed back the change in potential at said connection point of said FETs to the gates of both the main FET and the insulated-gate FET constituting the load.