Current Mirror Monitor for Wide-Bandwidth Isolated Current Sensing
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Solution Overview
Problem
Current monitors struggle to provide a precise measurement of AC- and DC-portions of current with high potential difference to ground potential across a wide frequency bandwidth range, with existing solutions either being sensitive to potential differences or having limited frequency bandwidth.
Innovation Solution
A current monitor with a constant current source in the second current branch, independent of potential differences, using a simple or Wilson current mirror circuit, and a resistive equivalence element to ensure output voltage independence from potential differences, along with a constant current source and diode assembly for temperature compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a simple current mirror circuit is used, then the frequency bandwidth range is broad, but the output signal strongly depends on the potential difference between the measuring point and reference potential
Solution Approach 1:
The current mirror is divided into two independent branches: a first current branch with the first semiconductor device and resistive equivalence element for signal generation, and a second current branch with the second semiconductor device and constant current source for stable current reference. This segmentation allows each branch to be optimized independently for bandwidth and potential difference independence respectively.
Solution Approach 2:
A constant current source is introduced as an intermediary element in the second current branch to decouple the current from potential difference variations. This constant current source acts as a mediator that provides a stable reference current independent of the potential difference between the measuring point and reference potential, thereby enabling the output signal to be independent from potential difference while maintaining broad frequency bandwidth.
2Measurement precision
If a Wilson current mirror circuit is used, then the output signal is independent from potential difference, but the frequency bandwidth range is reduced
Solution Approach 1:
The complex feedback and compensation structures of the Wilson current mirror that limit bandwidth are extracted and replaced. Only the essential current copying function is retained in a simplified two-branch current mirror configuration, while the potential difference independence is achieved through the constant current source in the second branch rather than through Wilson mirror feedback mechanisms.
Solution Approach 2:
The circuit topology is changed from a Wilson current mirror with multiple transistors and feedback paths to a simplified two-branch current mirror with a constant current source. This parameter change in circuit architecture eliminates the bandwidth-limiting feedback loops while maintaining potential difference independence through the constant current characteristic of the second branch.
3Stability of the object's composition
If resistive equivalence element with specific resistivity is used to match potentials, then temperature stability is improved, but the circuit complexity increases
Solution Approach 1:
The resistive equivalence element copies the resistive characteristics of the sensing element to establish a potential relationship between the two current branches. By setting the resistivity of the equivalence element equal to the sensing element resistivity, the circuit achieves temperature stability through matched potential drops without requiring additional complex compensation circuits.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a wide frequency bandwidth for measuring AC- and DC-portions of current with output voltage signals independent of potential differences, achieving a high frequency response and temperature stability.
Implementation Method 1
a current mirror circuit comprising a first semiconductor device and a second semiconductor device, both semiconductor devices electrically interconnected with each other for copying the current in the second semiconductor device to the first semiconductor device
Implementation Method 2
a resistive sensing element in a section of said current path
Data Source
AI summary
A current monitor for sensing the current in a current path includes a resistive sensing element in a section of the current path and a current mirror circuit having a first semiconductor device and a second semiconductor device. Both semiconductor devices electrically interconnect with each other for copying the current in the second semiconductor device to the first semiconductor device. The first semiconductor device is electrically connected to an electric reference potential and to a current input side of the section via a resistive equivalence element in a first current branch. The second semiconductor device is electrically connected to the electric reference potential and to a current output side of the section in a second current branch. The current monitor further includes a constant current source for keeping the current in the second current branch independent from the potential difference between the potential of the current output side of the section and the reference potential.