US 4,229,692 A · Linear low drift bridge amplifier

Abstract

A transducer bridge amplifier system includes a first operational amplifier having positive and negative inputs connected, respectively, to first and second output nodes of the bridge. The output of the operational amplifier is connected to a third node of the transducer bridge. A transducer of the transducer bridge is connected between the second node and the third node. A second operational amplifier has its positive input connected to ground and its negative input connected to the first node. A feedback resistor is coupled between the output of the second amplifier and a negative input of the second amplifier. An output signal produced by the second operational amplifier has a linear response to transducer deviation and low sensitivity to offset voltages of the first and second operational amplifiers. In a second alternate embodiment of the invention, the second operational amplifier has its output and its negative input connected to a negative terminal of a voltage supply biasing the transducer bridge amplifier system. The second operational amplifier has its positive input connected to the first node. The current flowing into the bridge system via the first node has linear response to transducer deviation and low sensitivity to affect voltages of the first and second operational amplifiers substantially independently of any impedance connected to the first node. In a third embodiment of the invention, the second operational amplifier can be omitted. A constant current source, rather than a constant voltage source, is used to bias the transducer bridge amplifier system. The current flowing into the first node biases linear response to transducer deviation and low sensitivity to offset voltage of the first operational amplifier.

Claims10

Dependent claims

A bridge amplifier circuit for linearly amplifying a transducer deviation signal produced by variations in resistance of a transducer of a transducer bridge, said transducer bridge including first, second, third, and fourth nodes, said transducer being connected between said second and third nodes, first resistance means being connected between said second and fourth nodes, second resistance means being connected between said fourth node and said first node, third resistance means being connected between said first node and said third node, a power supplying conductor being connected to said fourth node, said bridge amplifier circuit comprising in combination:

a. first amplifier means having a positive input, a negative input, and an output coupled to said first, second, and third nodes, respectively, for producing an increased or decreased current through said third resistance means in response to a positive variation in said transducer resistance or a negative variation in said transducer resistance, respectively, said increased or decreased current in said third resistance means acting to maintain said transducer bridge in a balanced voltage condition;
and
b. constant current maintaining means coupled between said first node and said fourth node for maintaining constant current in said first and second resistance means, whereby current flowing into or out of said bridge amplifier circuit through said first node is linearly related to said variations in resistance of said transducer.

Dependencies are inferred from the claim text.

Linear low drift bridge amplifier

Life of this patent

Linear low drift bridge amplifier

Life of this patent

Abstract

Claims10