Amplifier device for sensors

A physical quantity measuring system, comprising:

• an MOS dosimeter sensor equivalent to a variable voltage source (24) whose value is ETh, proving a purely capacitive impedance (26) whose value is CTh, wherein the additional impedance (12) proves a capacitive impedance C and wherein the following relations are satisfied:
• IG<I<I0
• VDS<VGSo<VT<0
• VGSo<ETh
• CTh/C>1
• where VT, IG, I0, VDS, VGSo and I respectively are a threshold voltage of a P channel field effect transistor used as a voltage control means, a gate current of the transistor, a polarization current of the transistor, a drain-source voltage of the transistor, an equilibrium gate-source voltage of the transistor and a current flowing in the sensor;
• and
• an amplifying device for said sensor, said amplifying device including:
• voltage control means (22) connected to output terminals (16, 20) of the sensor to maintain between said terminals a noticeably constant voltage;
• at least one additional impedance (12) series connected with the sensor in a polarization circuit between output terminals (18, 20) of said device, such that a same current flows into the sensor and into the additional impedance;
• and
• polarization means (14) providing the sensor and the additional impedance with said same current (I).