ADC Feedback Current Control for Low-Power Image Sensor Readout
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Solution Overview
Problem
Analog-to-digital converters (ADCs) used in image sensors face challenges in reducing power consumption while maintaining high resolution, leading to increased power consumption and potential degradation of image sensor performance.
Innovation Solution
The proposed solution involves an analog-to-digital converting circuit that utilizes a feedback mechanism, where a first amplifier generates output signals by comparing ramp and reset signals, and a second amplifier generates a second output signal based on these, with a counter converting pulses into digital signals. This feedback mechanism controls source currents of the amplifiers, reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If ADC processes many signals within unit time or provides improved resolution, then signal processing performance is improved, but power consumption increases
Solution Approach 1:
The patent applies dynamics by making the source current of the amplifier variable rather than fixed. The source current is dynamically adjusted based on the operating period (first or second operating period) and the state of the amplifier, allowing the circuit to adapt its power consumption to the actual processing needs, thus resolving the contradiction between processing performance and power consumption.
Solution Approach 2:
The patent implements periodic action by dividing the ADC operation into distinct first and second operating periods. During each period, different source current levels are applied to the amplifier based on whether comparison operation is being performed. This periodic switching allows high performance during active periods while reducing power consumption during idle or less demanding periods.
2Measurement precision
If ADC provides improved resolution, then signal processing performance is improved, but power consumption increases
Solution Approach 1:
The patent uses dynamic source current control to maintain high measurement precision only when needed. The source current is adjusted according to the operating period and amplifier state, providing sufficient current for high-resolution conversion during active periods while reducing current during idle periods, thus achieving high resolution without continuous high power consumption.
Solution Approach 2:
The patent changes the electrical parameter (source current) of the amplifier based on operational requirements. By varying the source current parameter between different operating periods and states, the circuit achieves high conversion precision when needed while minimizing power consumption during other times, resolving the contradiction between resolution and power usage.
Data Source
AI summary
Disclosed is a circuit which includes a first amplifier that generates a first output signal by comparing a ramp signal and a reset signal of a pixel signal output from a pixel array in a first operating period and comparing the ramp signal and an image signal of the pixel signal output from the pixel array in a second operating period, a second amplifier that generates a second output signal based on the first output signal, and a counter. During at least one operating period of the first operating period and the second operating period, the first output signal controls a first source current of the first amplifier, or the second output signal controls at least one of the first source current of the first amplifier and a second source current of the second amplifier.