Pixel Front End Circuit With Short Protection And Background Subtraction
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Solution Overview
Problem
Existing pixel front end technologies for photodetector arrays are susceptible to detector shorts and unable to effectively subtract unwanted dark current or background photocurrent, particularly at high bias voltages and currents, leading to increased complexity, expense, and reduced reliability in IR detector systems, which often require cryogenic temperatures for operation.
Innovation Solution
A pixel front end design that includes a p-type device and an n-type device connected in series with a voltage mode pixel backend, where one device acts as a switch and the other as a direct injection device, allowing for wide bias range and short protection, with optional background current subtraction capabilities using gate signal sampling and compensation currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high detector bias voltage is applied to maintain good linearity of photocurrent, then measurement precision is improved, but device reliability deteriorates due to increased susceptibility to detector shorts that can damage readout CMOS circuitry
Solution Approach 1:
The patent introduces a protective circuit configuration that acts as an intermediary between the high bias voltage source and the CMOS readout circuitry. This protective circuit includes current limiting elements and voltage clamping mechanisms that mediate the voltage transmission, allowing high bias voltages to be applied to the detector while preventing damaging current levels from reaching the CMOS circuitry. The protective circuit thus enables maintaining good linearity of photocurrent while protecting the readout circuitry from detector shorts.
2Device complexity
If passive amplifier with single FET transistor is used to reduce area and power, then device complexity is reduced, but measurement precision deteriorates due to inability to subtract background currents
Solution Approach 1:
The patent merges the background subtraction function with the existing passive amplifier circuit by integrating additional transistors that share common nodes and power supplies with the amplifier. The background subtraction circuit uses the same detector current path and combines the subtraction function with the amplification function in a unified circuit structure. This integration allows background current subtraction capability to be added while minimizing increases in pixel area and power consumption, as the new elements share resources with the existing amplifier.
3Measurement precision
If cryogenic temperatures are used to reduce background current, then measurement precision is improved, but device complexity and expense increase due to temperature control requirements
Solution Approach 1:
The patent replaces the mechanical/thermal approach of cryogenic cooling with an electronic approach using active background current subtraction circuits. Instead of physically lowering the temperature to reduce background current, the invention uses electronic circuitry to measure and subtract the background current component from the total detector signal. This substitution eliminates the need for complex cryogenic temperature control systems while achieving the same goal of improving measurement precision by removing background current effects.
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 provides increased maximum bias voltage range, protection from detector shorts, and effective background current subtraction, enabling operation at higher temperatures with improved reliability and reduced complexity, while maintaining linearity of photocurrent.
Implementation Method 1
connecting one p-type device and one n-type device with their channels in serial between one terminal of the detector, and a voltage mode pixel backend, and selectively depending on detector type, using one device as a switch, and the other as a direct injection device with the detector bias set by the gate voltage
Implementation Method 2
Many semiconductor photonic detectors (especially II-VI and III-V materials) operated in photoconductive mode must have voltage biases held relatively constant across their semiconductor junctions in order to maintain good linearity of a generated photocurrent, which is proportional to the incoming signal
Data Source
AI summary
Pixel Front end circuits particularly applicable to photodetectors requiring wide bias ranges and/or with high background currents. In various versions, wide bias ranges, short protection, and background current subtraction, both predetermined and automatically sampled, are disclosed.