Wheatstone bridge amplifier circuit with integrated diagnostic testing

A piezoresistive transducer with amplifier circuitry and diagnostic testing capability, said piezoresistive transducer comprising:

• a balanced sensing circuit for producing a differential output signal in response to a physical stimulus;
• an amplifier circuit including a differential amplifier having a first input and a second input to provide a differential input for amplifying differential input signals;
• a diagnostic test circuit coupled between the balanced circuit and the amplifier circuit, said diagnostic test circuit having a test input for receiving a test signal for activating a diagnostic testing mode, said diagnostic test circuit being operative to apply an offset voltage to the differential input of the amplifier circuit when in the diagnostic testing mode, said diagnostic test circuit including a first resistor connected in series to the first input of the differential amplifier and also coupled to a first current source, said diagnostic test circuit including a second resistor connected in series to the second input of the differential amplifier and also coupled to a second current source, wherein the first and second resistors have substantially equal resistance so as to provide a balanced transducer circuit;
• and
• an output coupled to the amplifier for providing an amplified output signal.

A method of performing diagnostic testing of a wheatstone bridge amplifier circuit, said method comprising the steps of:

• providing a differential input signal that is produced by a balanced circuit to first and second inputs of a differential amplifier;
• amplifying the differential input signal to produce an initial output signal;
• applying a known offset voltage to the differential input signal across the first and second inputs of the differential amplifier by applying a current signal to a resistor that is coupled in series to the first input of the differential amplifier and applying a second current source between a second resistor and the second input of the differential amplifier, wherein the first and second resistors have substantially equal resistance and the first and second current sources provides substantially equal current;
• amplifying the differential input signal with an amplifier when the offset voltage is applied to produce a test output signal;
• and
• comparing the initial output signal to the output test signal so as to test characteristics of the amplifier circuit.