Current Sensing Circuit with Feedback Loop for Offset Reduction
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Solution Overview
Problem
Current current sensing circuits in vehicles face challenges in accurately controlling fuel injection due to temperature-dependent resistance in field-effect transistors, leading to input offset issues in operational amplifiers, which increase circuit complexity and cost when attempting to mitigate these problems.
Innovation Solution
Incorporating two bipolar transistors connected to an operational amplifier, forming a feedback loop to maintain equal drain voltages across field-effect transistors, thereby reducing the input offset without increasing circuit complexity or cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an operational amplifier is added to eliminate temperature dependence influence, then the current mirror ratio stability is improved, but the input offset affects current sensing when operating current is small
Solution Approach 1:
The patent employs a feedback mechanism where the operational amplifier continuously adjusts the base voltages of the bipolar transistors to maintain equal drain voltages. This feedback loop compensates for both temperature dependence effects and input offset variations, simultaneously improving current mirror ratio stability and current sensing accuracy without compromising either parameter.
2Measurement precision
If techniques are developed to reduce operational amplifier input offset, then current sensing accuracy is improved, but circuit complexity and cost increase
Solution Approach 1:
The feedback loop formed by the operational amplifier and bipolar transistors automatically compensates for input offset without requiring additional complexity. The system self-adjusts to maintain equal drain voltages, eliminating the need for extra compensation circuits or complex offset reduction techniques.
Solution Approach 2:
The bipolar transistors serve as intermediaries between the field-effect transistors and the operational amplifier. They translate voltage differences into current adjustments that the operational amplifier can process, enabling offset compensation through a simple feedback mechanism rather than complex direct control.
3Measurement precision
If resistance Rdson of field-effect transistors is used for current sensing, then current mirror ratio is established, but temperature dependence influences the ratio
Solution Approach 1:
The operational amplifier in the feedback loop continuously monitors and adjusts the base voltages of the bipolar transistors to compensate for temperature-induced resistance changes. This maintains stable current mirror ratio despite variations in the temperature-dependent Rdson of the field-effect transistors.
Solution Approach 2:
The patent changes the operating parameters of the bipolar transistors through feedback control to counteract temperature effects. By dynamically adjusting base voltages in response to temperature variations, the system maintains constant current mirror ratio despite changes in field-effect transistor resistance.
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
This approach effectively reduces the influence of input offset on current sensing, maintaining accurate current measurement without adding complexity or cost to the circuit.
Implementation Method 1
forming a feedback loop to maintain equal drain voltages across field-effect transistors
Implementation Method 2
The resistance Rdson of the working field-effect transistor and the sensing field-effect transistor has a characteristic of temperature dependence, which influences the current mirror ratio
Data Source
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AI summary
The present utility model relates to a current sensing circuit and an integrated circuit, the current sensing circuit comprising:a second field-effect transistor for generating a sensing current proportional to a current flowing through a working circuit having a first field-effect transistor; a first bipolar transistor and a second bipolar transistor having bases connected together, wherein the emitters of the first bipolar transistor and the second bipolar transistor are respectively connected to the drains of the first field-effect transistor and the second field-effect transistor; an operational amplifier having its positive input and negative input connected to the collectors of the first bipolar transistor and the second bipolar transistor, respectively, and its output connected to the bases of the first bipolar transistor and the second bipolar transistor; and a third and fourth field-effect transistor for making the currents flowing through the first bipolar transistor and the second bipolar transistor the same. The current sensing circuit and integrated circuit can reduce the input offset of the operational amplifier without increasing the complexity or the cost of the circuit.