Differential Bridge Photodiode Circuit for Small Current Detection
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Solution Overview
Problem
Existing photodiode circuit arrangements for measuring small photo currents are complex, require additional external components, and suffer from self-heating issues, making them inaccurate and bulky.
Innovation Solution
A differential bridge circuit arrangement where two photodevices provide current flow in opposing directions without external power, using equivalent resistors and no operational amplifiers, allowing for balanced operation with net current zero, and enabling measurement of current differences through illumination variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional external components (operational amplifiers, power sources, capacitors) are added to the photodiode circuit, then the circuit can provide linear output and operate without bias, but the device complexity and bulkiness increase
Solution Approach 1:
The patent extracts and removes the operational amplifiers and external power sources from the photodiode circuit, retaining only the essential photodiodes and resistors. This extraction eliminates the need for complex biasing circuits while maintaining the ability to measure small photo currents through the bridge configuration's inherent differential measurement capability.
Solution Approach 2:
The bridge circuit is designed to be self-biasing through the photodiodes' own current generation. The circuit uses the photo currents themselves to create the necessary voltage drops across the resistors, eliminating the need for external power sources and operational amplifiers. The differential measurement is achieved automatically through the bridge's balanced configuration.
2Measurement precision
If complex circuit arrangements with multiple operational amplifiers are used, then measurement capability is improved, but self-heating and overheating occur affecting measurement accuracy
Solution Approach 1:
The patent removes operational amplifiers and external power sources that generate heat, retaining only passive components (photodiodes and resistors). This extraction eliminates the primary sources of self-heating while preserving the ability to detect small photo currents through the bridge configuration's differential measurement approach.
Solution Approach 2:
The circuit operates using only the energy from incident light on the photodiodes, without external power sources. The photo currents generated directly drive the bridge measurement, eliminating the need for active components that would generate heat and affect measurement accuracy.
3Power
If photodiodes are arranged to face the same direction in a Wheatstone bridge, then current generation is maximized, but additional active elements are required to handle the unidirectional current flow
Solution Approach 1:
The patent introduces asymmetry in the bridge configuration by arranging photodiodes to face opposite directions on adjacent arms. This asymmetric arrangement creates opposing current flows that naturally balance the bridge without requiring additional active elements. The asymmetric configuration allows direct differential measurement of photo currents while maintaining current generation efficiency.
4Ease of operation
If external power sources and operational amplifiers are added to the circuit, then the circuit can operate and provide output, but the bulkiness of the device increases
Solution Approach 1:
The patent extracts and removes external power sources and operational amplifiers from the circuit, relying solely on the photodiodes' inherent current generation capability. This extraction dramatically reduces device bulkiness while maintaining operability through the bridge configuration's passive differential measurement mechanism.
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 solution simplifies the circuit, reduces self-heating, and provides accurate measurement of small photo current differences without external power sources, enhancing measurement precision and reducing bulkiness.
Implementation Method 1
two photodevices provide current flow in opposing directions... enabling measurement of current differences through illumination variations
Data Source
AI summary
A bridge circuit arrangement, method of providing said bridge circuit arrangement, and uses thereof are described. The bridge circuit arrangement comprises a first photodevice configured on a first arm, a second photodevice configured on a second arm, a first resistor configured on a third arm, and a second resistor configured on a fourth arm of the bridge. The first and second photodevice provide current flow.