==If I have a passive sensor then both Norton and Thervenin equivalents becomes the same equivalent, my sensor behaves just as an impedance==, so my sensor is this one:
So now I'm considering this operating and not that there is no sources. Obviously this kind of sensor will need an excitation. ==So the readout circuit, the conditioning circuit or front end circuit should contain an amplifier, but also a power supply a source of voltage or current, depending on the sensor, even an ADC (Analogic to Digital converter) if needed. So front-end electrocnics are related to the electronics needed to read the sensor, to operate and use the sensor==.