MOSFET Current Detection Circuit for Small Signal Separation
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Solution Overview
Problem
Conventional current detection circuits fail to detect small signal components due to minimal voltage changes in resistors, making it difficult to separate DC and signal components in input currents from photodiodes, especially in the presence of ambient light.
Innovation Solution
A current detection circuit comprising an input port, rectifying element, capacitor, MOS transistors, and voltage detection circuits, which utilize capacitive charging and discharging to amplify voltage changes for detecting small signal components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional current detection circuits use resistors to detect current changes, then the circuit structure is simple, but the detection precision is insufficient when current change is very small
Solution Approach 1:
The patent introduces a rectifying element as an intermediary component between the photodiode and the detection circuit. This rectifying element converts the small current changes from the photodiode into voltage changes that can be more effectively detected and amplified by subsequent circuit stages, thereby improving detection precision without requiring direct measurement of minute current variations.
Solution Approach 2:
The patent replaces the conventional resistor-based voltage detection method with a field-effect transistor (FET) based detection mechanism. The FET's gate terminal detects voltage changes corresponding to current changes, and its transconductance amplifies these changes. This substitution of the detection mechanism from direct resistive voltage measurement to FET-based transconductance amplification significantly improves detection precision for very small current changes.
2Measurement precision
If the current change due to signal component is very small, then the DC component from ambient light dominates, but conventional circuits cannot detect the small signal component
Solution Approach 1:
The patent extracts and separately processes the DC component and signal component through the rectifying element and capacitor combination. The capacitor blocks the DC component while allowing AC signal components to pass, effectively separating the harmful DC offset from the useful signal. This extraction approach enables detection of small signal components even when dominated by large DC current from ambient light.
Solution Approach 2:
The patent utilizes the voltage-dependent transconductance parameter of the FET to amplify small voltage changes. By operating the FET in a region where its transconductance is high and stable, the circuit amplifies small signal-induced voltage changes while maintaining immunity to large DC current variations from ambient light, thus improving signal detection capability in the presence of harmful DC offsets.
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
Enables the detection of very small current changes in input currents, effectively separating DC and signal components even in the presence of ambient light, by adjusting sensitivity through transconductance coefficients in current mirror circuits.
Implementation Method 1
A current detection circuit according to the present invention utilizes charging and discharging of a capacitor to amplify voltage changes
Implementation Method 2
A current detection circuit comprises an input port, an output port, a rectifying element, a capacitor, a first first conductivity type MOS transistor, and a voltage detection circuit
Data Source
AI summary
A current detection circuit includes: an input port; an output port; a rectifying element; a capacitor; a first first conductivity type MOS transistor; and a voltage detection circuit. The input port is connected to an anode terminal of the rectifying element, the drain terminal of the first first conductivity type MOS transistor, and a voltage detection terminal of the voltage detection circuit. A cathode terminal of the rectifying element is connected to a first terminal of the capacitor and a gate terminal of the first first conductivity type MOS transistor. A second terminal of the capacitor and a source terminal of the first first conductivity type MOS transistor are connected to a first power source terminal. A detection result output port of the voltage detection circuit 105 is connected to the output port.