Pixel RAMP Generator Controller Synchronizing Timing for Noise Reduction
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Solution Overview
Problem
Conventional CMOS image sensor architectures face challenges in achieving high-performance image sensing with low noise and power efficiency, particularly due to noise contributions from ramp generator circuits and asynchronous timing in analog-to-digital conversion processes, which affect image quality and power consumption.
Innovation Solution
The implementation of a pixel ramp generator controller that synchronizes ramp and clock signaling through a ramp-to-clock synchronizer, clock-to-ramp synchronizer, and ramp timing controller to generate corrected signals, ensuring precise timing and synchronization, thereby reducing row-temporal noise and improving power efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a same ramp voltage is shared across an entire row of pixels for analog-to-digital conversion, then the device complexity is reduced and power consumption is lowered, but row-temporal noise increases and measurement precision deteriorates
Solution Approach 1:
The patent divides the single shared ramp generator into multiple segmented ramp generators, with each ramp generator serving a specific segment or group of pixels within the row. This segmentation allows each ramp generator to operate independently with its own synchronized timing, reducing the coherent noise that affects all pixels when using a single shared ramp generator. The segmentation maintains reduced device complexity compared to having completely independent ramp generators for each pixel while improving measurement precision through localized noise reduction.
2Ease of operation
If ramp generation and clock signaling are asynchronous, then the device operation is simpler and power consumption is lower, but timing synchronization accuracy deteriorates and noise increases
Solution Approach 1:
The patent implements a feedback mechanism where the ramp generator controller receives timing information from the pixel conversion process and adjusts its ramp generation timing accordingly. The controller monitors the clock signaling and synchronizes ramp voltage transitions to occur at precise moments during the clock cycles. This feedback-based synchronization maintains relatively simple controller operation while significantly improving timing accuracy and reducing noise compared to completely asynchronous operation.
Solution Approach 2:
The patent employs preliminary action by pre-synchronizing the ramp generator timing to the clock signal before actual pixel conversion begins. The controller prepares the ramp generation timing in advance, ensuring that ramp transitions are aligned with clock edges before the conversion process starts. This preliminary synchronization setup maintains operational simplicity during conversion while establishing the precise timing relationships needed for accurate measurement and reduced noise.
3Measurement precision
If strict timing synchronization is implemented for ramp and clock signaling, then measurement precision and image quality improve, but device complexity increases and power consumption rises
Solution Approach 1:
The patent implements a universal ramp generator controller that handles multiple functions: generating ramp voltages, synchronizing with clock signals, timing pixel conversions, and managing multiple ramp generators. By consolidating these diverse functions into a single multi-functional controller, the patent achieves strict timing synchronization for improved measurement precision without proportionally increasing device complexity. The universal controller reduces the need for separate dedicated circuits for each function.
Solution Approach 2:
The patent utilizes parameter changes by dynamically adjusting the timing parameters of ramp generation based on clock signal characteristics and conversion requirements. The controller modifies ramp transition timing, duration, and amplitude parameters in response to synchronization needs, achieving precise timing control through software or logic-based parameter adjustment rather than through complex hardwired timing circuits. This approach improves measurement precision while keeping the physical circuit complexity manageable.
Data Source
AI summary
Techniques are described for controlling operation of a pixel conversion ADC in a manner that enforces strict timing and synchronization of ramp and clock signaling. Synchronizing techniques can be applied to generate a corrected ramp start signal based on synchronizing a received ramp start signal to an input clocking signal, and to generate a controller clock signal based on synchronizing an input clocking signal to the corrected ramp start signal. The corrected ramp start signal and the controller clock signal can be used to control generation of a ramp enable signal for controlling timing of pixel ramp voltage generation digital pixel conversion counting, and to control generation of an output clocking signal used by the digital pixel conversion counting.