Trimmed Ramp Generator Circuit for Faster Image Sensor Settling
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Solution Overview
Problem
The ramp settling time of the ramp signal in image sensors limits the maximum frame rate, reducing the performance of image sensors due to delays in the analog to digital conversion process.
Innovation Solution
Incorporating trimming inputs and tunable input circuitry in the ramp generator to reduce the ramp settling time by compensating for parasitic capacitance and current effects, which delays the ramp signal, thereby improving the frame rate and performance of image sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional ramp generator is used without trimming circuitry, then the device complexity is low, but the ramp settling time is long which limits the maximum frame rate
Solution Approach 1:
The trimming circuitry is configured to compensate for parasitic capacitance effects before the ramp signal is generated and before settling time begins. By pre-adjusting the ramp generator parameters to account for known parasitic effects, the circuit achieves faster settling without requiring complex real-time correction mechanisms during operation.
Solution Approach 2:
The trimming circuitry acts as an intermediary between the ramp generator and the comparator. It introduces adjustable compensation elements that mediate the interaction between the ramp signal and parasitic capacitances, allowing optimization of the settling behavior without fundamentally changing the core ramp generation or comparison functionality.
2Loss of time
If trimming inputs and tunable input circuitry are added to the ramp generator, then the ramp settling time is reduced, but the device complexity increases
Solution Approach 1:
The trimming circuitry enables adjustment of key parameters in the ramp generator, such as current levels and voltage thresholds, to optimize settling time. By providing controlled variability in these parameters through trimming inputs, the system can be tuned to achieve faster settling without requiring a complete redesign of the ramp generation architecture.
Solution Approach 2:
The tunable input circuitry introduces dynamic adjustability to the ramp generator, allowing parameters to be modified based on operating conditions. This dynamic capability enables the system to adapt to different parasitic effects and optimize performance for various frame rate requirements, rather than being fixed at a single operating point.
3Measurement precision
If the ramp generator operates without compensation for parasitic effects, then the device complexity is low, but the analog to digital conversion accuracy is reduced due to delays
Solution Approach 1:
The trimming circuitry incorporates feedback mechanisms that monitor the ramp signal behavior and adjust compensation parameters accordingly. By using feedback from the actual settling behavior to fine-tune the compensation, the system achieves higher conversion accuracy while keeping the added complexity manageable through iterative self-correction rather than over-engineering.
Data Source
AI summary
A ramp generator includes an integrator including a first stage having first and second inputs and first and second outputs, and a second stage including first and second transistors coupled between a power supply rail and ground. A node between the first and second transistors is coupled to the output of the integrator amplifier. A control terminal of the first transistor is coupled to the first output of the first stage, and a control terminal of the second transistor is coupled to the second output of the first stage. A first current flows from the output to ground during a ramp event in the ramp signal generated from the output. Trimming circuitry is coupled to the output of the integrator amplifier to provide a second current to the output of the integrator amplifier in response to trimming inputs. The second current substantially matches the first current.