Image Sensor Comparator Bandwidth Switching for Low-Noise ADC
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Solution Overview
Problem
Existing image pickup apparatuses using column parallel AD converters face challenges in reducing noise while maintaining frame rate, as fixed bandwidth limitation in comparators is inadequate when ramp reference voltage inclination varies, leading to increased inversion delay and insufficient noise reduction.
Innovation Solution
The apparatus dynamically adjusts the bandwidth of comparators based on the rate of change of the ramp reference signal by using a control unit to switch capacitance values, allowing for broader bandwidth when the inclination is smaller and narrower bandwidth when it is larger, thereby optimizing noise reduction and frame rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If fixed bandwidth limitation is applied to comparators, then noise reduction is achieved, but inversion delay increases when ramp reference voltage inclination varies
Solution Approach 1:
The patent applies dynamics by making the bandwidth limitation capacitance variable rather than fixed. The control unit dynamically adjusts the capacitance value based on the inclination of the ramp reference voltage, allowing the comparator bandwidth to adapt to different operating conditions. This resolves the contradiction by enabling noise reduction when needed while maintaining fast response when the ramp inclination requires it.
Solution Approach 2:
The patent changes the parameter of capacitance value in the bandwidth limitation circuit based on the ramp reference voltage inclination. By varying the capacitance parameter according to operating conditions, the system achieves both noise reduction (when larger capacitance is applied) and maintains fast inversion (when smaller capacitance is applied), resolving the fixed bandwidth limitation problem.
2Measurement precision
If bandwidth of comparators is narrowed to reduce noise, then signal-to-noise ratio improves, but frame rate decreases
Solution Approach 1:
The system dynamically adjusts the comparator bandwidth based on the ramp reference voltage inclination. When the ramp inclination is small, the bandwidth is narrowed to improve S/N ratio. When the ramp inclination is large, the bandwidth is widened to maintain frame rate. This dynamic adjustment resolves the contradiction between noise reduction and frame rate maintenance.
Solution Approach 2:
The capacitance value parameter in the bandwidth limitation circuit is changed based on the ramp reference voltage inclination. This parameter change allows the system to optimize the balance between noise reduction and frame rate performance according to actual operating conditions, rather than being constrained by a fixed bandwidth setting.
3Device complexity
If fixed capacitance is used for bandwidth limitation, then device complexity is reduced, but adaptability to varying ramp reference voltage inclination is insufficient
Solution Approach 1:
The patent implements a dynamic bandwidth limitation circuit where the capacitance value can be adjusted based on the ramp reference voltage inclination. The control unit monitors the inclination and adjusts the capacitance accordingly, providing adaptability to varying operating conditions while maintaining reasonable circuit complexity through systematic control.
Solution Approach 2:
The system uses feedback by monitoring the ramp reference voltage inclination and adjusting the bandwidth limitation capacitance based on this information. The control unit receives information about the ramp characteristics and adjusts the capacitance value to optimize performance, creating a closed-loop system that adapts to varying conditions.
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
This approach effectively reduces noise and maintains a high frame rate by adaptively controlling the comparator bandwidth in response to varying ramp reference signal inclinations, improving the signal-to-noise ratio and noise characteristics.
Implementation Method 1
a pixel configured to generate a signal by photoelectric conversion
Data Source
AI summary
An image pickup apparatus includes a pixel generating a signal by photoelectric conversion, a comparator comparing the signal based on the pixel with a reference signal varied with time, a counter performing counting until the comparator outputs a signal indicating that a relationship in magnitude between the signal based on the pixel and the reference signal is reversed, and a control unit. The comparator includes a first amplifier receiving the reference signal at a first input portion and the signal based on the pixel at a second input portion to compare the signal based on the pixel with the reference signal. The control unit sets a bandwidth of the comparator to a first bandwidth when the reference signal varies at a first rate of change and to a second bandwidth when the reference signal varies at a second rate of change.