Image Sensor Precharge Pulse Control Under PVT Variation
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Solution Overview
Problem
CMOS image sensors face challenges in stably generating precharge pulses due to variations in Process, Voltage, and Temperature (PVT) conditions, which affect the precharge time and sensing margin of sense amplifiers, making it difficult to guarantee consistent detection performance.
Innovation Solution
The image sensor employs a precharge controller that generates divided clock signals and selects specific clock signals based on PVT conditions to control the pulse width of the precharge signal, ensuring stable precharge operations by combining these signals to maintain a consistent pulse width and phase, thereby stabilizing the precharge operation across varying conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional precharge circuit is used without PVT compensation, then the circuit structure is simple, but the precharge pulse width varies under different Process, Voltage, and Temperature conditions, causing unstable sensing margin and detection performance
Solution Approach 1:
The precharge controller dynamically selects different divided clock signals based on PVT conditions to maintain stable precharge pulse width. The circuit transitions from a static fixed-width pulse generator to a dynamic selector that adapts to varying process, voltage, and temperature conditions by choosing appropriate clock division ratios (e.g., 1/2, 1/4, 1/8) to compensate for PVT-induced variations.
Solution Approach 2:
The invention changes the parameter of clock signal division ratio to compensate for PVT variations. By providing multiple divided clock signals with different division ratios and selecting the appropriate one based on PVT conditions, the system adjusts the precharge pulse width parameter to maintain consistent sensing performance across varying environmental and operational parameters.
2Reliability
If the precharge pulse width is extended to ensure adequate precharging, then the sensing margin improves, but the detection time increases and frame rate decreases
Solution Approach 1:
The system dynamically adjusts the precharge pulse width by selecting different divided clock signals based on actual PVT conditions rather than using a fixed extended pulse width. This allows the circuit to use the minimum necessary precharge time for each condition, optimizing the trade-off between sensing margin and detection speed.
Solution Approach 2:
The invention optimizes the precharge pulse width parameter by selecting from multiple divided clock signals with different durations. This parameter optimization ensures adequate precharging for reliable detection while minimizing the precharge time to maintain high frame rates, resolving the contradiction between sensing margin and productivity.
Data Source
AI summary
An image sensor for stably generating pulses of a precharge signal is disclosed. The image sensor includes a divider configured to generate a plurality of divided clock signals by dividing one or ore input clock signal, a precharge pulse generator configured to generate a first pulse signal by selecting any one of the plurality of divided clock signals in response to decoding signals of a first group, and generate a second pulse signal by selecting any one of the plurality of divided clock signals in response to decoding signals of a second group, and a precharge signal generator configured to generate a precharge signal by combining the first pulse signal and the second pulse signal.