Amplifiers – With periodic switching input-output
Patent
1988-12-09
1990-02-20
Mullins, James B.
Amplifiers
With periodic switching input-output
324715, H03F 338
Patent
active
049029819
ABSTRACT:
A circuit for physical placement within an underground well to amplify low level differential DC voltage signals measured at a well casing is disclosed. The circuit incorporates an instrument amplifier with a first switching device before the amplifier and an inverter after the amplifier in the signal path. A second switching device selectively connects one of the amplifier and inverter outputs to a low-pass filter. The switching devices operate synchronously under control of an operating clock signal so that DC error terms associated with the amplifier are converted into a substantially AC error signal while maintaining the signal being amplified as a DC signal. The duty cycle of the operating clock signal is established to cause the substantially AC error signal to include a DC component of appropriate polarity and magnitude to compensate for DC error terms associated with the inverter and low-pass filter. The low-pass filter removes AC components, leaving an amplified DC output signal which is compensated for DC error terms of the circuit components. In addition, circuits for generating digital duration codes which define the operating clock signal duty cycle and which vary in accordance with environmental conditions are disclosed.
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Ser. No. 889,572 filed 7/24/86 by Gard.
Gard Michael F.
Goodwill William P.
Atlantic Richfield Company
Mills Jerry
Mullins James B.
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