Image Sensor Charge Pump Timing to Reduce Supply Ripple
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Solution Overview
Problem
Image sensor performance is affected by supply noise in circuits used to read image data from image cells, necessitating effective management and reduction techniques.
Innovation Solution
An image sensor design incorporating a voltage generator with charge pump cells and a delay line to generate clock signals, where the delay between clock signals is controlled by delay line elements, minimizing noise by distributing ripple energy across the delay period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If charge pump cells are used to generate power supply voltage, then power supply voltage can be generated, but supply noise and ripple are introduced affecting image sensor performance
Solution Approach 1:
The charge pump circuit is divided into multiple charge pump cells (first charge pump cell, second charge pump cell, etc.) that operate in parallel. Each cell processes charge independently and contributes to the overall power supply voltage, distributing the ripple generation across multiple independent units rather than a single source.
Solution Approach 2:
The charge pump cells are controlled by clock signals with different phases. The first charge pump cell operates on a first clock signal while the second charge pump cell operates on a second clock signal that is phase-shifted relative to the first. This periodic staggering causes ripple waves from different cells to occur at different times, allowing them to cancel each other out through destructive interference.
2Power
If multiple charge pump cells operate simultaneously, then power supply current is increased, but ripple waves add up causing more noise
Solution Approach 1:
Clock signal generation circuits generate phase-shifted clock signals for different charge pump cells. The first clock signal and second clock signal have different phases, causing the charge pump cells to operate at different times within the overall cycle. This temporal separation ensures that when one cell is generating ripple, another is not, preventing constructive addition of ripple waves while maintaining continuous power supply current.
Solution Approach 2:
The clock signal generation circuits are configured in advance to provide phase-shifted clock signals to different charge pump cells. This preliminary phasing arrangement ensures that ripple waves from multiple cells are naturally staggered in time, allowing them to cancel each other out before reaching the power supply node, thus preventing noise accumulation.
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 effectively reduces supply noise in image sensor circuits, enhancing image sensor performance by minimizing ripple noise and ensuring stable power supply voltages.
Implementation Method 1
a delay line including a plurality of delay line elements configured to generate the plurality of clock signals, where a first charge pump cell receives a first clock signal generated by a first delay line element, where a second charge pump cell receives a second clock signal generated by a second delay line element, and where a delay between the first clock signal and the second clock signal is determined by the delay line
Implementation Method 2
a plurality of charge pump cells, each configured to receive one of a plurality of clock signals and to source charge to the first power supply node in response to the received one clock signal
Data Source
AI summary
An image sensor includes image sensor cells generating an image signal in response to one or more control signals, and a first driver generating a first control signal. The first driver includes a first positive supply terminal connected to a first power supply node. The image sensor also includes a voltage generator generating a first voltage at the first power supply node, where the voltage generator includes charge pump cells to receive clock signals and to source charge to the first power supply node, a delay line including delay line elements generating clock signals, where a first charge pump cell receives a first clock signal generated by a first delay line element, where a second charge pump cell receives a second clock signal generated by a second delay line element, and where a delay between the first clock signal and the second clock signal is determined by the delay line.