High Frame Rate Focal-Plane Array With Interleaved Subarrays
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Solution Overview
Problem
Achieving high frame rates for thermal imaging with bolometer or microbolometer arrays is hindered by long bias times required for accurate readings, which can lead to low frame rates due to heating issues and infrastructure limitations in data conversion.
Innovation Solution
Implementing a high frame rate focal-plane array (FPA) and readout integrated circuit (ROIC) structure that concurrently biases multiple rows of IR sensors, uses specialized column circuitry for simultaneous signal processing, and employs pipelined operations to achieve frame rates of up to 1000 Hz, with features like interleaved subarrays and offset current normalization to manage bias heating and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If bolometer arrays use traditional sequential biasing methods, then measurement precision is maintained, but frame rate is limited to low values due to long bias times
Solution Approach 1:
The detector array is divided into multiple subarrays that can be biased and read out in parallel. This segmentation allows simultaneous processing of multiple rows or columns, dramatically increasing the frame rate while maintaining measurement precision through dedicated readout circuits for each subarray
Solution Approach 2:
The system employs periodic pulsing of bias currents to the bolometer elements, allowing rapid sequential access to different rows or columns. This periodic action enables high frame rates by efficiently managing the bias time required for accurate measurements without continuous power consumption
2Measurement precision
If bias time is extended for accurate readings, then measurement precision improves, but heating issues worsen and frame rate decreases
Solution Approach 1:
The bias current is applied in periodic pulses rather than continuously, allowing the bolometer elements to cool between measurements. This periodic pulsing maintains measurement precision during the bias window while reducing average temperature and heating issues
Solution Approach 2:
Offset currents are pre-applied to compensate for drift and heating effects before actual measurements are taken. This preliminary action establishes a baseline that accounts for thermal effects, allowing accurate readings without extending bias time and reducing cumulative heating
3Productivity
If data conversion infrastructure is increased to support high frame rates, then productivity improves, but device complexity increases
Solution Approach 1:
The readout integrated circuit is divided into multiple parallel channels, each handling a subset of the detector array. This segmentation distributes the data conversion load across multiple simpler channels rather than requiring one complex high-speed converter, reducing overall device complexity while supporting high frame rates
Solution Approach 2:
The system transitions from sequential single-channel readout to parallel multi-channel architecture, adding a spatial dimension to data conversion. Multiple readout paths operate simultaneously, increasing throughput without requiring each individual conversion path to be excessively complex
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
Enables high-speed thermal imaging with frame rates of 500 Hz to 1000 Hz for VGA-sized systems, suitable for fast-moving objects and applications requiring rapid response times, while maintaining low noise and accurate signal processing.
Implementation Method 1
A bolometer detects particular bands of electromagnetic radiation (such as IR) by exposing a thermally isolated material that absorbs these bands to a source of the radiation and measuring the temperature increase in the absorbing material
Implementation Method 2
A resistive thermometer can be connected to two ends of the material, and current can be driven through the material to measure the resistance, which changes with the temperature of the material
Implementation Method 3
An FPA is an array of detectors on which incoming radiation is focused
Data Source
AI summary
A focal-plane array includes: an array of thermal sensors arranged in at least 120 rows and at least 160 columns, the thermal sensors being divided among three or more subarrays; and bias circuitry to concurrently pulse bias the thermal sensors of one of the rows of each of the subarrays, and to sequentially bias the rows of each of the subarrays at a rate of at least 40,000 rows per second. A readout integrated circuit includes: a sensing area to physically and electrically connect to the array of thermal sensors and includes row circuitry to perform the concurrent pulse biasing and the sequential biasing, and column circuitry to concurrently measure analog signals from the pulse-biased thermal sensors; and conversion circuitry to convert the measured analog signals to corresponding digital signals. In some embodiments, the thermal sensors are operated without cooling. In some embodiments, the rows are interleaved between the subarrays.