Segmented Capacitive Voltage Ramp Generator for Low-Noise ADCs
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Solution Overview
Problem
Existing voltage ramp generators for analog-to-digital converters in image sensors face challenges in achieving high signal-to-noise ratio (SNR) and non-linearity, particularly in terms of noise and power supply voltage rejection ratio.
Innovation Solution
A circuit design comprising a first capacitance array, a differential amplifier, and a capacitive feedback circuit, where capacitive elements are organized in sets and controllably coupled to the amplifier input, allowing for adjustable conversion gain and reduced noise through selective use of capacitive elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a voltage ramp generator is used in analog-to-digital converters, then conversion capability is provided, but noise increases and signal-to-noise ratio deteriorates
Solution Approach 1:
The capacitive array is divided into multiple independent capacitive elements that can be selectively activated. By segmenting the total capacitance into discrete controllable units, the circuit can optimize the number of active elements based on the required conversion gain, thereby minimizing noise while maintaining measurement precision.
Solution Approach 2:
The circuit dynamically adjusts the number of active capacitive elements based on the required conversion gain. This dynamic reconfiguration allows the system to optimize performance for different operating conditions, reducing noise by using only the necessary number of capacitive elements rather than keeping all elements permanently active.
2Adaptability or versatility
If conversion gain is adjusted in voltage ramp generators, then adaptability improves, but non-linearity increases
Solution Approach 1:
The capacitive array is segmented into multiple individually controllable elements. By selectively activating specific segments (capacitive elements) based on the required conversion gain, the system achieves adaptability while maintaining linearity through precise digital control of each segment's contribution to the total capacitance.
3Object-generated harmful factors
If capacitive elements are selectively coupled to amplifier input, then noise is reduced, but device complexity increases
Solution Approach 1:
The capacitive array is segmented into independently controllable elements with individual switching control. This segmentation enables selective activation of only the necessary capacitive elements, reducing noise by minimizing the number of active components while the modular structure keeps the control logic manageable.
Solution Approach 2:
The circuit incorporates control logic that automatically determines the optimal number of capacitive elements to activate based on the required conversion gain. This self-adjusting capability reduces the need for external complex control mechanisms, allowing the system to optimize noise performance autonomously.
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 reduces noise and maintains adjustable conversion gain, improving the signal-to-noise ratio and line noise in CMOS Image Sensors while preserving the ability to adjust the conversion gain or slope of the ramp.
Implementation Method 1
a capacitive feedback circuit coupling the output of said differential amplifier to said first input
Data Source
AI summary
A circuit includes a first capacitance array formed by n nominally equal capacitive elements. A first electrode of each capacitive element is coupled, via respective switches to either a reference voltage or ground. A differential amplifier has a first input coupled to an output of a first capacitance array, a second input grounded, and an output generating a voltage ramp. A capacitive feedback circuit couples the output of the differential amplifier to the first input. A second capacitance array has an output coupled to the first input of the differential amplifier. The capacitive elements of the first capacitance array are organized in sets. The circuit operates by controllably coupling, set by set, second electrodes of the capacitive elements of the first capacitance array to the first input of the differential amplifier.