Leakage-Biased Differential Amplifier for Nanoamp Current Sensing
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Solution Overview
Problem
Current sensing transducers that exhibit small changes in resistance due to external stimuli generate extremely small currents, necessitating a highly sensitive current sensor capable of accurately detecting these minute changes.
Innovation Solution
A differential amplifier configuration with matched leakage currents and semiconductor resistors, including FETs and ESD protection, is employed to detect small currents flowing through the transducer, allowing for precise measurement of currents as low as a fraction of a nanoampere.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional current sensing circuits are used, then the circuit can operate with standard components, but the sensitivity is insufficient to detect extremely small currents (nanoamperes) generated by certain transducers
Solution Approach 1:
The patent changes the operating parameters of the differential amplifier by biasing each node with a leakage current instead of using conventional biasing methods. This parameter change enables the circuit to operate in a regime where it can detect extremely small currents while maintaining stability through the matched leakage currents.
Solution Approach 2:
The patent converts the typically harmful leakage current into a beneficial biasing mechanism. By intentionally introducing matched leakage currents to bias the differential amplifier nodes, the circuit achieves the sensitivity needed to detect nanoampere-level signals, turning a source of error into a functional advantage.
2Measurement precision
If the resistance change of the transducer is extremely small, then the transducer can respond to subtle external stimuli, but the generated current is extremely small and difficult to detect
Solution Approach 1:
The patent modifies the electrical parameters of the sensing circuit by using leakage current biasing, which changes the operating point of the differential amplifier to be suitable for detecting extremely small currents generated by transducers with minimal resistance changes.
Solution Approach 2:
The differential amplifier configured with leakage current biasing acts as an intermediary that bridges the gap between the extremely small transducer current and the measurement system, amplifying the subtle signals while maintaining the sensitivity required for detecting minute resistance changes.
3Measurement precision
If a differential amplifier is biased conventionally, then the circuit is easier to design, but it cannot achieve the required sensitivity for detecting fraction of nanoampere currents
Solution Approach 1:
The patent employs parameter changes by modifying the biasing conditions of the differential amplifier to use leakage currents, which enables high sensitivity detection while maintaining a relatively simple differential amplifier topology that is familiar to circuit designers.
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 enables the detection of very small currents, enhancing the sensitivity of current sensors and enabling accurate detection of changes in external stimuli, such as in disk drive applications.
Implementation Method 1
the first node 4A is biased by a first leakage current 14A and the second node 4B is biased by a second leakage current 14B such that the output 6 represents a current flowing through the transducer 10
Implementation Method 2
A current sensing circuit typically comprises a suitable transducer that responds to an external stimulus... the resistance of a current sensing transducer changes in response to the external stimulus so that when a bias voltage is applied to the transducer, the change in resistance caused by a change in the external stimulus results in a corresponding change in current passing through the transducer
Data Source
AI summary
A current sensor is disclosed comprising a differential amplifier including a first node, a second node, and an output. The current sensor further comprises a first resistor having a first end coupled to the first node and a second end for coupling to a transducer, and a second resistor having a first end coupled to the second node and a second end. When the second end of the second resistor is unconnected and the differential amplifier is driven with a supply voltage, the first node is biased by a first leakage current and the second node is biased by a second leakage current such that the output represents a current flowing through the transducer.