Infrared Sensor Column Amplifier Bias Removal Circuit
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Solution Overview
Problem
Conventional uncooled infrared sensors face challenges in achieving high sensitivity and large gain due to the dominance of bias current components, leading to insufficient dynamic range and increased noise levels, which complicates the design and costs of infrared cameras.
Innovation Solution
The implementation of a column amplifier with a first and second amplifying transistor, along with clamp circuits, to remove bias components and enhance signal amplification, allowing for increased gain and reduced noise through precise voltage control and threshold voltage management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a bias current is applied to the column amplifier to improve gain, then the amplification capability is enhanced, but the storage capacitor becomes saturated by the bias current component, reducing the dynamic range
Solution Approach 1:
The patent segments the current components by introducing a dedicated bias current removal circuit that separates the bias current component from the signal component. The column amplifier processes both components together, while the removal circuit selectively eliminates the bias current, allowing the storage capacitor to maintain adequate dynamic range for signal storage.
Solution Approach 2:
The patent extracts the bias current component from the total current using a specialized removal circuit. This circuit measures the bias current component and generates a compensating signal to subtract it from the amplifier output, effectively removing the harmful bias current saturation effect while preserving the useful signal.
2Measurement precision
If the gain of the column amplifier is increased to amplify weak infrared signals, then signal sensitivity is improved, but external circuit noise becomes more significant, increasing system cost
Solution Approach 1:
The patent applies preliminary action by removing the bias current component before it can saturate the storage capacitor and before external noise can be amplified. The bias current removal circuit operates continuously to eliminate this offset, ensuring that the storage capacitor maintains its full dynamic range for capturing weak infrared signals without being compromised by subsequent external noise.
3Device complexity
If a MOS transistor is used to remove the bias current component, then the column amplifier saturation is prevented, but the threshold voltage fluctuation of the MOS transistor limits the precision of bias component removal
Solution Approach 1:
The patent implements feedback by continuously measuring the bias current component and using this information to generate a compensating signal. The bias current removal circuit monitors the amplifier output and adjusts its compensation signal dynamically, ensuring precise removal of the bias current component despite variations in transistor threshold voltages.
Solution Approach 2:
The patent introduces an intermediary bias current removal circuit that acts as a mediator between the column amplifier and the storage capacitor. This circuit processes the amplifier output, removes the bias current component through dedicated transistors configured for this purpose, and provides a cleaned signal to the storage capacitor, isolating the amplifier from saturation issues.
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 higher sensitivity and a wider dynamic range for infrared sensors, reducing noise and lowering the cost of infrared camera production by effectively isolating and amplifying the infrared signal component.
Implementation Method 1
an infrared sensor that uses a silicon pn junction which converts a temperature change into a voltage change
Implementation Method 2
The uncooled type, or heat-type, infrared solid-state imaging device converts an incident infrared ray, having a wavelength of about 10 microns, into heat in an absorption structure
Data Source
AI summary
An infrared sensor includes an imaging area including infrared detection pixels; row selection lines; a signal line; a row selection circuit generating a column voltage in the signal line; a column amplifier including a first amplifying transistor which generates an amplification voltage obtained by amplifying the column voltage and a first clamp circuit which holds threshold voltage information of the first amplifying transistor in its gate; a removing circuit including a second amplifying transistor and a second clamp circuit which holds threshold voltage information of the second amplifying transistor in its gate, the removing circuit being connected to the column amplifier to remove a bias component from the amplification voltage; and a reading circuit reading an output voltage from the column amplifier, the output voltage is obtained by excluding at least the bias component from the amplification voltage.