Digital Voltmeter Topology Offset Cancellation
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Solution Overview
Problem
Existing digital voltmeter designs face performance limitations due to sensitivity to input amplifier feedback offset drift, which is not effectively canceled by current methods, despite improved observation times.
Innovation Solution
A digital voltmeter circuit topology with two inputs (HI and LO) and a floating DVM within a guard shield, where the input amplifier's offset and feedback offset are canceled by routing inputs between the gain amplifier and floating circuit ground, using a buffer amplifier for polarity reversal without charge pump-out, and a conductive enclosure to minimize capacitance and coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If zero cycle measurement is used to remove input amplifier offset, then offset is removed, but observation time is reduced
Solution Approach 1:
The patent implements periodic reversal of the input amplifier configuration between two measurement cycles. In the first cycle, the amplifier is configured normally; in the second cycle, it is reversed. This periodic action allows offset cancellation through differential measurement while maintaining continuous observation of the input signal without requiring separate zero-cycle measurements.
2Measurement precision
If reversing input amplifier is used to cancel offset, then offset is cancelled, but feedback offset drift is not cancelled and limits performance
Solution Approach 1:
The patent introduces a feedback mechanism where the output of the second measurement is fed back to the first measurement through the reversed amplifier configuration. This feedback loop enables the system to compensate for feedback offset drift by using the reversed amplifier's output to correct the original measurement, thereby maintaining measurement precision while addressing the performance limitation.
3Productivity
If high observation time is maintained, then measurement efficiency is improved, but sensitivity to feedback offset drift increases
Solution Approach 1:
The patent segments the measurement process into two distinct measurement cycles with reversed amplifier configurations. This segmentation allows the system to maintain high observation efficiency by performing measurements continuously while using the reversed configuration in the second cycle to cancel offset and feedback offset drift effects, thereby achieving both high productivity and measurement precision.
Data Source
AI summary
A system may include two input terminals, e.g., HI and LO, and a floating circuit that is physically separate from the input terminals and includes a gain amplifier. The floating circuit can be surrounded by a conductive enclosure that is electrically connected to the second input terminal. The floating circuit can further switch between input signals received from the first and second input terminals to the gain amplifier and the floating circuit ground.