Active Eyewear Front-End Circuit for Low-Power 3D Imaging
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Solution Overview
Problem
Active eyewear systems for 3D imaging face challenges due to high power consumption from complex transimpedance amplifier (TIA) circuitry, which reduces battery life and is prone to noise and interference, especially from infrared signals and ambient light.
Innovation Solution
A simplified front-end circuit with a common base input device, current mirrors, and an operational transimpedance amplifier (OTA) with a compensating impedance and cancellation loop circuitry, which reduces current drain, noise, and effectively rejects interference, providing a current output for a current mode variable gain amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a transimpedance amplifier (TIA) is used to convert current signal from photodiodes to voltage signal, then the signal conversion is achieved, but power consumption increases and battery life is reduced
Solution Approach 1:
The circuit is divided into two stages: a first stage using a common base amplifier for low-noise current-to-voltage conversion, and a second stage using a voltage-to-current converter. This segmentation allows each stage to be optimized for its specific function, reducing overall power consumption compared to a single complex TIA circuit.
Solution Approach 2:
The patent changes the operating parameters by using a common base amplifier configuration instead of a traditional TIA, and by implementing a voltage-to-current converter in the second stage. These parameter changes optimize the circuit for lower power consumption while maintaining signal conversion functionality.
2Reliability
If a transimpedance amplifier (TIA) is used for signal conversion, then signal processing is achieved, but noise and interference from infrared signals and ambient light increase
Solution Approach 1:
The patent implements feedback mechanisms in both the common base amplifier stage and the voltage-to-current converter stage. This feedback allows the circuit to actively compensate for noise and interference signals, improving signal processing quality by rejecting unwanted infrared and ambient light interference.
Solution Approach 2:
The patent introduces an intermediate voltage-to-current converter stage between the photodiode current output and the final signal processing. This intermediary stage acts as a buffer that isolates and filters noise and interference signals while preserving the useful signal components.
3Difficulty of detecting and measuring
If a complex transimpedance amplifier circuit is used, then signal conversion capability is improved, but device complexity increases
Solution Approach 1:
The complex signal conversion function is segmented into two simpler, specialized stages: a common base amplifier for initial current-to-voltage conversion and a voltage-to-current converter for final signal conditioning. This segmentation reduces overall circuit complexity while maintaining or improving signal conversion capability.
Solution Approach 2:
The patent replaces the traditional mechanical/electronic TIA circuit with a combination of common base amplifier and voltage-to-current converter, which uses different circuit topologies to achieve the same signal conversion function with reduced complexity and improved performance.
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 reduces power consumption, minimizes noise generation, and enhances interference rejection, extending battery life and improving the reliability of 3D active eyewear systems by efficiently processing infrared synchronization signals.
Implementation Method 1
Active eyewear 20, having a left lens 22 and a right lens 24, is provided with one or more I/R photodiodes 26 that are sensitive to the I/R synchronization signal 18. The photodiodes 26 are also sensitive to I/R interference 28 created by, for example, sunlight 30, incandescent light 32 and fluorescent light 34.
Data Source
AI summary
A circuit includes a front-end circuit, a receiver stage and a controller. An example front-end circuit includes a common base input device, a first current mirror and a second current mirror, where the common base input device has its emitter coupled to a photodiode, its collector coupled to an input of the first current mirror, and its base coupled to a reference voltage to reverse bias the photodiode and where an output of the first current mirror is input into the second current mirror. In another example, a voltage drop resistor is coupled to a cancellation signal output of the first current mirror and an operational transimpedance amplifier (OTA) has inputs coupled to the voltage drop resistor and to a reference voltage and an output coupled to a compensating impedance and to a control input of a variable current source designed to feed the emitter signal input.