CMOS Image Sensor Ramp Signal Generation Circuit
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Solution Overview
Problem
CMOS image sensors face challenges in generating reliable ramp signals due to influence from ground noise, which affects the quality of output images.
Innovation Solution
A ramp signal generation circuit is designed with a switch and capacitor configuration that isolates the reference voltage storage from external ground noise, using a band gap reference unit, amplifiers, and an integrator to generate a noise-reduced ramp signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the band gap reference unit is continuously connected to provide reference voltage, then the reference voltage is continuously available for ramp signal generation, but ground noise affects the reliability of the ramp signal
Solution Approach 1:
The reference voltage is stored in advance in a storage capacitor before ramp signal generation begins. The switch connects the band gap reference unit to charge the capacitor during a preset period, then disconnects before the ramp signal is generated. This preliminary action ensures the reference voltage is ready while avoiding noise contamination during the actual conversion process.
Solution Approach 2:
The harmful influence of ground noise is extracted and isolated by disconnecting the band gap reference unit from the ramp signal generation path. The switch removes the reference voltage source from the signal path after charging the storage capacitor, effectively separating the noise-prone reference generation from the sensitive ramp conversion process.
2Object-affected harmful factors
If the switch disconnects the storage unit from the band gap reference unit, then noise influence is reduced, but the reference voltage must be stored in advance
Solution Approach 1:
The switch operates periodically, connecting the band gap reference unit to charge the storage capacitor during a preset period, then disconnecting for the ramp signal generation phase. This periodic connection and disconnection ensures the reference voltage is replenished regularly while maintaining noise isolation during the critical conversion period.
3Object-affected harmful factors
If the reference voltage is stored in a capacitor connected to external ground, then noise filtering is improved, but the circuit complexity increases
Solution Approach 1:
The storage capacitor serves multiple functions: it stores the reference voltage, filters noise through its connection to external ground, and provides a stable voltage source during ramp signal generation. By making the capacitor multi-functional, the patent avoids adding separate filtering components, thus limiting the increase in circuit complexity.
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
The solution improves the reliability of the ramp signal generation, reducing noise influence and enhancing the overall operation characteristics of the CMOS image sensor.
Implementation Method 1
a band gap reference unit configured to provide a reference voltage having a predetermined voltage level
Implementation Method 2
a storage unit configured to store the reference voltage
Implementation Method 3
a ramp signal generation unit configured to receive an input voltage corresponding to the reference voltage stored in the storage unit and generate a ramp signal
Data Source
AI summary
An image sensor includes a band gap reference unit configured to provide a reference voltage having a predetermined voltage level, a storage unit configured to store the reference voltage, a switch configured to selectively connect the storage unit to the band gap reference unit, and a ramp signal generation unit configured to receive an input voltage corresponding to the reference voltage stored in the storage unit and generate a ramp signal.