ADC Bias Voltage Control for Image Sensor Noise Reduction
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Solution Overview
Problem
The existing CMOS image sensors with analog-to-digital converters (ADCs) face challenges due to the introduction of on-resistance from power-down switches, which affect the input range and noise levels, particularly in correlated double sampling methods.
Innovation Solution
The proposed solution eliminates the need for a separate power-down switch by dynamically adjusting the bias voltage based on operation modes, using transistors to control metal lines and optimize bias voltage application in the ADCs, thereby reducing noise and stabilizing the input range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a power-down switch is used to reduce power consumption when the ADC is not in use, then power consumption is reduced, but on-resistance is introduced which causes the input range of the amplifier to vary and increases noise
Solution Approach 1:
The invention extracts and removes the power-down switch from the ADC circuit. Instead of using a physical switch to power down the ADC, the patent applies bias voltage to control the operation state of the ADC, thereby eliminating the source of on-resistance and its associated noise and input range variation problems while still achieving power savings when needed.
Solution Approach 2:
The invention changes the control parameter from a binary power-down switch state to a continuous bias voltage level. By adjusting the bias voltage applied to the ADC circuit, the patent can control the operation state (active or standby) without introducing the harmful on-resistance of a physical switch, thus resolving the contradiction between power savings and signal quality.
2Adaptability or versatility
If a power-down switch is introduced to enable power management, then power management capability is improved, but device complexity increases due to additional components
Solution Approach 1:
The bias voltage generator serves multiple functions: it provides the necessary bias voltage for ADC operation, controls the power state of the ADC (active or standby), and eliminates the need for a separate power-down switch. This multi-functionality reduces device complexity while maintaining power management capability.
Solution Approach 2:
The invention merges the power control function into the existing bias voltage generation circuitry. Instead of having a separate power-down switch, the bias voltage controller integrates the power management function by selectively applying bias voltage to the ADC, thereby reducing the number of components and simplifying the overall circuit architecture.
3Object-affected harmful factors
If the ADC is kept active to avoid noise from power-down switches, then noise is reduced, but power consumption increases
Solution Approach 1:
The invention implements dynamic control of the ADC operation state through adjustable bias voltage. The ADC can be dynamically switched between active and standby states by controlling the bias voltage level, allowing the system to optimize between noise performance and power consumption based on real-time operational requirements without the drawbacks of a fixed power-down switch.
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 minimizes noise, reduces power consumption, and enhances the efficiency of the image sensor by eliminating the need for physical power-down switches, leading to improved image processing and reduced circuit complexity.
Implementation Method 1
a first transistor and a second transistor configured to determine a path of the bias voltage applied to the first metal line and the second metal line
Data Source
AI summary
An image sensor supporting a full resolution mode and a crop mode, the image sensor including: a pixel array including a plurality of pixels configured to generate a pixel signal by sensing an object; an analog-to-digital converter configured to convert the pixel signal into a digital signal and including a plurality of metal lines; a bias generator configured to apply a bias voltage to the plurality of metal lines; and a bias controller including: a first transistor configured to activate all of the plurality of metal lines based on a first control signal; and a second transistor configured to activate a first metal line for the crop mode among the plurality of metal lines based on a second control signal.