Floating Point Image Sensor Readout Circuitry
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Solution Overview
Problem
High-resolution analog-to-digital converters (ADCs) in imaging devices consume significant power, occupy large die area, and require long conversion times, making it challenging to achieve efficient high-resolution imaging.
Innovation Solution
Implementing a floating-point image sensor readout scheme that separates the image signal into an exponent and mantissa conversion, allowing the use of lower resolution ADCs, which reduces power consumption and die area usage, while maintaining high dynamic range through adjustable ADC reference voltage levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-resolution ADCs are used to achieve high image resolution and dynamic range, then measurement precision is improved, but power consumption increases significantly
Solution Approach 1:
The patent segments the high-resolution ADC conversion process into two separate lower-resolution conversions: an exponent conversion stage and a mantissa conversion stage. This segmentation allows each stage to use lower-resolution ADCs (e.g., 6-bit ADCs instead of 12-bit ADCs), significantly reducing power consumption while maintaining the equivalent of high-resolution conversion through the combination of exponent and mantissa results.
2Measurement precision
If high-resolution ADCs are used to achieve high image resolution, then measurement precision is improved, but die area increases
Solution Approach 1:
The patent divides the single high-resolution ADC into two separate lower-resolution ADCs operating in sequence. Each lower-resolution ADC requires significantly less die area than a single high-resolution ADC would require. The segmented architecture processes the signal through exponent conversion followed by mantissa conversion, achieving high effective resolution while minimizing total converter area.
3Measurement precision
If high-resolution ADCs are used to achieve high image resolution, then measurement precision is improved, but conversion time increases
Solution Approach 1:
The patent segments the conversion process into two parallelizable lower-resolution conversion stages. Each stage completes its conversion more quickly than a single high-resolution conversion would take. The exponent conversion and mantissa conversion can be performed in sequence with optimized timing, reducing the total conversion time compared to a single high-resolution ADC while maintaining measurement precision.
4Use of energy by moving object
If lower-resolution ADCs are used to reduce power consumption and die area, then power consumption and die area are reduced, but measurement precision deteriorates
Solution Approach 1:
The patent employs dynamic reference voltage adjustment where the ADC reference voltage is changed between the exponent conversion stage and the mantissa conversion stage. This dynamic adaptation allows lower-resolution ADCs to achieve high effective measurement precision by optimizing the reference voltage for each conversion stage, thereby compensating for the lower individual resolution while maintaining overall measurement accuracy.
Solution Approach 2:
The patent changes key parameters including the ADC reference voltage level and the conversion approach between exponent and mantissa stages. By adjusting the reference voltage dynamically and using floating-point representation with separate exponent and mantissa conversions, the system achieves high measurement precision equivalent to high-resolution ADCs while using lower-resolution converters, thus resolving the contradiction between resolution and power/area efficiency.
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 speeds up ADC conversion times, reduces power consumption, and decreases die area, enabling efficient high-resolution imaging without compromising dynamic range.
Implementation Method 1
Each pixel may include a photosensor such as a photodiode that receives incident photons (light) and converts the photons into electrical signals
Data Source
AI summary
An image sensor may include an array of image sensor pixels arranged in rows and columns. Each image pixel arranged along a given column may be coupled to analog-to-digital converter (ADC) circuitry that is capable of converting analog pixel signals into a digital floating point equivalent representation. The ADC circuitry may be configured to perform exponent conversion during a first time period at a nominal reference voltage level and to perform mantissa conversion a subsequent time period at an adjustable reference voltage level that can be less than the nominal reference voltage level. Readout circuitry implemented in this way can perform conversion in a shorter period of time using a reduced resolution ADC to serve effectively as a higher resolution ADC.