Isolation Amplifier Offset Compensation Using Feedback Current Control
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Solution Overview
Problem
Isolation amplifiers in motor drives and renewable energy systems face performance issues due to systematic offset voltages that are difficult to compensate despite careful design, affecting accuracy requirements.
Innovation Solution
An offset voltage compensation circuit is introduced, comprising a pair of amplifiers, current sources, and resistors, which are strategically placed in the last output stage to adjust and eliminate output offset voltages by controlling currents and resistances, ensuring accurate voltage compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If careful IC circuit, layout or package design is used to compensate offset voltage, then offset voltage compensation is improved, but certain systematic offset still remains and affects performance
Solution Approach 1:
The patent implements a feedback mechanism where the output voltages of the first and second amplifiers are monitored, and the first current source is controlled according to the difference between these output voltages to generate a compensation current. This compensation current is injected into the second input of the first amplifier to eliminate the output offset voltage, creating a closed-loop feedback system that continuously corrects offset errors.
Solution Approach 2:
The patent introduces a compensation current as an intermediary element that mediates between the output offset voltage error and the final corrected output. The first current source generates this compensation current based on the voltage difference, and this intermediate current signal is used to adjust the differential pair output, effectively decoupling the offset error from the final output.
2Measurement precision
If compensation circuit is added to eliminate systematic offset, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent merges the offset compensation function with the existing differential output stage by integrating the first current source and compensation components directly into the output circuitry. The compensation circuit shares the same amplifiers and output nodes as the main signal path, eliminating the need for separate compensation circuits and reducing overall device complexity.
Solution Approach 2:
The first amplifier serves multiple functions: it amplifies the differential input signal and simultaneously receives the compensation current to correct offset errors. The first current source also serves dual purposes by providing bias current to the first amplifier and generating the compensation current based on output voltage differences, reducing the need for additional dedicated compensation components.
Data Source
AI summary
An offset voltage compensation circuit and an isolation amplifier device including the same are provided. The offset voltage compensation circuit includes a first amplifier, a second amplifier, a first current source, a second current source, a first resistor and a second resistor. The first amplifier has a first input connected to a first differential input node and a first output connected to a first differential output node. The second amplifier has a first input connected to a second differential input node and a second output connected to a second differential output node. The first current source is connected to the first amplifier for providing a first current. The second current source is connected to the second amplifier for providing a second current. The first current source is controlled according to the second current and a difference between a first initial output voltage and a second initial output voltage.