Adjustable Current Source for Image Sensor Column Settling
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Solution Overview
Problem
As image sensors increase in pixel resolution and frame rate, there is a challenge in ensuring timely and unattenuated signal readout, which can lead to signal attenuation or excessive power consumption.
Innovation Solution
The implementation of adjustable current source and slew rate sensing and current source control circuitry in the readout circuitry, which dynamically adjusts the bias current based on the slew rate of the signal to ensure fast and unattenuated readout while minimizing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If image sensor resolution and frame rate are increased, then imaging quality and temporal resolution are improved, but readout time becomes insufficient leading to signal attenuation
Solution Approach 1:
The patent applies dynamics by making the current source adjustable rather than fixed. The bias current is dynamically modified based on the slew rate of the signal, allowing the system to adapt to varying readout conditions. This enables sufficient settling time for high-resolution, high-frame-rate imaging while maintaining the ability to readout signals quickly when needed.
Solution Approach 2:
The patent changes the parameter of bias current in the current source based on the slew rate of the signal. By monitoring the slew rate and adjusting the bias current accordingly, the system optimizes the settling time for each readout operation, ensuring accurate signal readout without requiring excessive time for all cases.
2Speed
If higher bias current is used to speed up settling, then readout speed is improved, but power consumption increases
Solution Approach 1:
The system dynamically adjusts the bias current based on actual slew rate conditions rather than operating at a constant high current. This allows the circuit to consume higher power only when fast settling is actually needed, reducing overall power consumption while maintaining the capability for fast readout when required.
Solution Approach 2:
The bias current parameter is changed according to the slew rate of the signal. When the slew rate is high, a higher bias current is applied to speed up settling. When the slew rate is low, the bias current is reduced to minimize power consumption. This adaptive parameter adjustment resolves the contradiction between speed and energy efficiency.
Data Source
AI summary
An image sensor may include an array of imaging pixels arranged in rows and columns. Each column of imaging pixels may be coupled to a respective column output line. Each column output line may be coupled to readout circuitry that includes an adjustable current source, sample and hold circuitry, and slew rate sensing and current source control circuitry. To decrease the settling time of the column output line, the slew rate sensing and current source control circuitry may increase the magnitude of a bias current provided by the adjustable current source when the slew rate of the output voltage is above a threshold. When the slew rate of the output voltage is below the threshold, the bias current may revert to a lower magnitude to conserve power.