Ramp A/D Converter Noise Control for Preserving Dynamic Range
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Solution Overview
Problem
Conventional A/D converters used in CMOS image sensors face a challenge in maintaining a large dynamic range for signal components during image capture, especially when increasing the gain, as the noise component's full scale voltage is multiplied along with the signal component, leading to a reduction in the dynamic range available for photoelectric conversion.
Innovation Solution
An A/D converter with a ramp voltage generation circuit, a voltage comparison circuit, a counter, and a latch circuit, along with an averaging process circuit and control circuit that adjusts the counting start timing and reference voltage level based on the difference between the average noise voltage and a target noise voltage, ensuring the dynamic range is maintained without relying on the gain setting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If gain is increased to improve signal component amplification, then signal component amplification is improved, but dynamic range for signal component is reduced due to noise component multiplication
Solution Approach 1:
The patent segments the dynamic range allocation by separately handling signal component and noise component. The full scale voltage is divided into distinct portions: one allocated to the signal component and another to the noise component. This segmentation allows the signal component to utilize a larger portion of the dynamic range while the noise component occupies a controlled portion, thereby resolving the contradiction between signal amplification and dynamic range preservation.
Solution Approach 2:
The patent applies local quality by assigning different voltage allocation characteristics to different components. The signal component is given preferential treatment with a larger allocated portion of the full scale voltage, while the noise component is assigned a smaller, controlled portion. This differentiated allocation strategy enables enhanced signal amplification without proportionally increasing noise impact, thus maintaining the dynamic range for signal components.
2Measurement precision
If gain is increased to improve image quality, then image quality is improved, but dynamic range is reduced because full scale voltage is shared with noise component
Solution Approach 1:
The patent segments the full scale voltage into distinct allocations for signal and noise components. By dividing the voltage resource in this manner, the system can achieve high measurement precision for image quality through adequate signal amplification while simultaneously preserving dynamic range by limiting the noise component's voltage share. This segmentation resolves the contradiction between image quality improvement and dynamic range maintenance.
Solution Approach 2:
The patent implements local quality by providing differentiated voltage allocation to different signal components. The useful signal component receives a larger portion of the full scale voltage to ensure high measurement precision and image quality, while the noise component is restricted to a smaller portion. This localized quality enhancement strategy enables improved image quality without sacrificing overall dynamic range.
3Reliability
If full scale voltage is allocated to noise component during gain adjustment, then noise component handling is improved, but dynamic range for signal component is reduced
Solution Approach 1:
The patent applies local quality by assigning different priority levels and voltage allocations to different components. The signal component, which is critical for dynamic range, is given high priority with a larger allocated portion of the full scale voltage. The noise component, while important for reliability, is assigned a smaller, controlled portion. This differentiated allocation ensures reliable noise handling while preserving adequate dynamic range for signal components.
Data Source
AI summary
An A/D converter comprises a ramp voltage generation circuit, a voltage comparison circuit comprising an arithmetic unit comparing an analog voltage to be converted with a reference voltage showing the voltage change of a ramp voltage, and changing an output when the reference voltage equals the analog voltage, a counter counting and outputting a digital value corresponding to the reference voltage, a latch circuit latching and outputting the digital value when the output of the voltage comparison circuit changes, an averaging process circuit to obtain an average noise voltage, a target noise voltage setting circuit setting a target noise voltage, and a control circuit adjusting at least one of a counting start timing of the counter with respect to a control reference timing, or the criterion level of the reference voltage at the counting start timing, based on a difference between the average noise voltage and the target noise voltage.