Physical quantity sensing device with bridge circuit and temperature compensating method

A physical quantity sensing device comprising:

• an AC voltage generator arranged to generate an AC voltage;
• and
• a bridge circuit that has first and second input points, to which the AC voltage is applied, and first and second output points, which are connected to a differential amplifier;
• wherein
• the bridge circuit includes a first sensor element, an impedance of which changes with a physical quantity to be measured, and a second sensor element, an impedance of which also changes with the physical quantity to be measured, the first and second sensor elements having a positive temperature characteristic having a sensitivity that increases as temperature rises;
• the AC voltage generator includes an oscillator and an amplitude limiter arranged to supply the AC voltage, an amplitude of which is limited within a predetermined range, in response to an output signal of the oscillator;
• and
• the amplitude limiter has a negative temperature characteristic that decreases the amplitude of the AC voltage with a rise in temperature and the negative temperature characteristic of the amplitude limiter is substantially equal to the positive temperature characteristic of the first and second sensor elements of the bridge circuit, thereby compensating for temperature dependence of a differential voltage produced between the first and second output points.