Semiconductor sensor self-checking circuit

Claim 1

A self-checking circuit for use with a semiconductor sensor including a semiconductor substrate having a cantilever, and piezo resistors formed in said cantilever and connected in a bridge circuit having first and second output terminals, a first voltage source for supplying a predetermined driving voltage to drive said bridge circuit, and a differential amplifier connected to said first and second output terminals for producing an output signal corresponding to a stress produced in said cantilever, the self-checking circuit comprising: a second voltage source; a first resistor having a first resistance; a second resistor having a second resistance to provide a difference between the first and second resistances; first switching means responsive to a checking signal for connecting said first output terminal to said second voltage source through said first resistor; second switching means responsive to said checking signal for connecting said second output terminal to said second voltage source through said second resistor, said second voltage source being connected to said first and second switching means for providing a predetermined control voltage to said first and second resistors via said first and second switching means, respectively; and means for producing said checking signal to said first switching means and at the same time to said second switching means.