Photovoltaic Image Array Zero-Bias Readout With Orthogonal Multiplexing
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Solution Overview
Problem
Photovoltaic detector arrays face challenges in operating at zero bias voltage due to complex circuitry requirements and excessive burst noise, which limits their room temperature operation and increases the number of electrical interconnects and transistors needed.
Innovation Solution
The implementation of orthogonal code multiplexing for photovoltaic detector currents, using Walsh-Hadamard Codes and Pseudo Noise Codes, allows for the operation of multiple detectors at zero bias voltage with reduced circuitry, eliminating dark current and 1/f noise, and minimizing the number of electrical interconnects and transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If photovoltaic detectors are operated at zero bias voltage, then dark current and 1/f noise are eliminated, but complex circuitry with many electrical interconnects and transistors is required
Solution Approach 1:
Multiple photovoltaic detector currents are combined into a single multiplexed current signal using orthogonal codes. The ROIC integrates currents from multiple detectors through shared circuitry, merging what would otherwise require separate processing paths. This combining approach reduces the number of electrical interconnects and transistors needed while maintaining the ability to distinguish individual detector signals through code-based separation.
Solution Approach 2:
The ROIC circuitry is designed to handle multiple detector currents simultaneously through a single multiplexed input path. The same circuit components serve multiple detectors by processing their coded current signals in parallel, making the circuitry universal rather than dedicated to each individual detector. This multi-functionality reduces overall device complexity while preserving signal integrity.
2Device complexity
If multiple photovoltaic detectors are multiplexed using orthogonal codes, then the number of electrical interconnects and transistors is reduced, but signal-to-noise ratio must be maintained
Solution Approach 1:
Orthogonal codes are applied to photovoltaic detector currents before they are combined in the ROIC. This preliminary coding action embeds identification information in each detector's current signal, allowing the system to separate and reconstruct individual detector signals after multiplexing. The pre-coding ensures that even with reduced circuitry, the signal-to-noise ratio is preserved because the orthogonal codes provide a mathematical framework for clean signal separation.
3Temperature
If photovoltaic image array operates at room temperature, then cooling requirements are eliminated, but dark current increases
Solution Approach 1:
The operating bias voltage parameter is changed from a positive voltage that generates dark current to zero bias voltage. This parameter change eliminates the electrical field that drives dark current generation while still allowing photovoltaic detectors to respond to incident photons. By operating at zero bias, the system achieves room temperature operation without the penalty of increased dark current, as the photovoltaic effect generates signal current without requiring forward bias.
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 enables improved room temperature operation with enhanced signal-to-noise ratio, reduced noise performance, and simplified fabrication of photovoltaic image arrays, allowing for efficient imaging without cooling and increased space for additional circuitry on the substrate.
Implementation Method 1
photovoltaic detector arrays face challenges in operating at zero bias voltage
Data Source
AI summary
The invention implements room temperature imaging of a photovoltaic diode image array operating in any spectral band (visible through extreme thermal). The invention also operates the photo diodes at zero bias voltage and thus eliminates 1/f (burst) noise and dark current. And the invention simplifies the electrical-mechanical interface between the readout integrated circuit (ROIC) and the photodetector array and minimizes the component count on the ROIC. These advantages are realized by multiplexing the photocurrents from each photodiode in the array according to an orthogonal or biorthogonal code set. The multiplexed current is supplied to an op amp such that zero bias is maintained for the photodetector array. The code set also allows the photocurrent generated by each photodiode to be recovered.