Current Sensing Circuit With Filter Gain Compensation
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Solution Overview
Problem
Conventional current sensing circuits experience reduced sensing accuracy due to changes in the magnification ratio caused by the presence of filter resistors in the sensing path.
Innovation Solution
A current sensing circuit with a compensation path, utilizing transistors and resistors to control the ratio of currents flowing through the sensing and compensation paths, decoupling the magnification ratio from the resistance of filter resistors by matching transistors and selecting appropriate resistor ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a filter circuit including filter capacitor and filter resistor is disposed on sensing path, then filtering performance is improved, but sensing accuracy deteriorates due to gain change
Solution Approach 1:
The patent divides the sensing circuit into separate functional blocks: a filter circuit block (with RF and CF) and a sensing amplifier block. The filter circuit is electrically isolated from the sensing path by using the amplifier's high input impedance, so the filter resistor RF does not affect the gain calculation. This segmentation allows independent optimization of filtering and sensing functions without mutual interference.
Solution Approach 2:
The amplifier acts as an intermediary between the filter circuit and the sensing path. Its high input impedance prevents current from flowing through the filter resistor RF, effectively decoupling the filter resistor from the sensing gain calculation. This intermediary element allows the filter circuit to be placed near the sensing resistor without compromising measurement accuracy.
2Reliability
If filter resistor is included in sensing path, then filtering is achieved, but magnification ratio becomes dependent on filter resistor resistance
Solution Approach 1:
The circuit is segmented into filtering function (handled by RF and CF) and amplification function (handled by the amplifier). The amplifier's high input impedance creates an electrical separation that prevents RF from being included in the gain calculation, simplifying the magnification ratio to depend only on known resistor values R1 and R2.
Solution Approach 2:
The patent changes the operating parameters of the amplifier to have very high input impedance, which fundamentally alters the circuit behavior. This parameter change ensures that negligible current flows through RF, making the filter resistor's value irrelevant to the gain calculation and simplifying the overall system.
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
Maintains good sensing accuracy by isolating the magnification ratio from the influence of filter resistor resistances, ensuring consistent and accurate current sensing.
Implementation Method 1
amplifier AMP, a first resistor R1, a second resistor R2, a third resistor R3, a first transistor M1 and a second transistor M2C. The filtering circuit is coupled to a first input terminal + of the amplifier AMP through the first resistor R1. The other terminal of the filter capacitor CF is coupled to a second input terminal - of the amplifier AMP
Implementation Method 2
A control terminal of the first transistor M1 is coupled to an output terminal of the amplifier AMP, and a first terminal of the first transistor M1 is coupled to the first input terminal + of the amplifier AMP and a second terminal of the first transistor M1 is grounded through the second resistor R2. A control terminal of the second transistor M2C is coupled to the output terminal of the amplifier AMP, and a first terminal of the second transistor M2C is coupled to the second input terminal - of the amplifier AMP and a second terminal of the second transistor M2C is grounded through the third resistor R3
Implementation Method 3
The other terminal of the filter capacitor CF is coupled to the second input terminal - of the amplifier AMP. The first terminal of the filter capacitor CF is coupled between the first resistor R1 and the first filter resistor RF1. The other terminal of the first filter resistor RF1 is coupled to the first terminal of the sensing resistor RSEN
Data Source
AI summary
A current sensing circuit includes a filtering circuit, an amplifier, a first resistor, a first transistor and a second transistor. The filtering circuit is coupled to two terminals of a sensing resistor. The amplifier has a first input terminal, a second input terminal and an output terminal. The second input terminal is coupled to the filtering circuit. The first resistor is coupled between the filtering circuit and the first input terminal of amplifier. A control terminal of the first transistor is coupled to the output terminal of amplifier, and its first terminal is coupled to the first input terminal of amplifier and its second terminal is grounded through a second resistor. A control terminal of the second transistor is coupled to the output terminal of amplifier, and its first terminal is coupled to the second input terminal of amplifier and its second terminal is grounded through a third resistor.