Column Amplifier Transistor Ratio Optimization for CMOS Sensor Noise
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Solution Overview
Problem
CMOS imaging sensors face challenges with output noise and current consumption in readout circuitry, particularly due to limitations in gain bandwidth and slew rate, which are critical for high-performance imaging applications like mega-pixel sensors.
Innovation Solution
The design of a column amplifier with a specific ratio of channel ratios between series-connected transistors, allowing for improved gain bandwidth and slew rate while reducing current consumption, achieved by optimizing the channel width and length ratios of transistors within the amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional amplifier designs are used in CMOS readout circuitry, then current consumption is reduced, but gain bandwidth and slew rate are limited resulting in higher output noise and slower signal settling
Solution Approach 1:
The patent changes the channel width-to-length ratio parameter of the transistors in the amplifier circuit. Specifically, it uses a first transistor with a channel width-to-length ratio of approximately 2:1 and a second transistor with a ratio of approximately 1:2, creating an asymmetric configuration that optimizes the balance between noise performance and power consumption without requiring excessive bias current
2Speed
If amplifier gain bandwidth and slew rate are increased to reduce output noise, then signal settling improves, but current consumption increases
Solution Approach 1:
The patent optimizes transistor parameters including channel width, channel length, and biasing conditions to achieve high slew rate and gain bandwidth. The asymmetric transistor ratio configuration enables faster charge/discharge rates at the output node, improving signal settling speed while maintaining moderate current consumption levels suitable for mega-pixel sensor applications
3Use of energy by moving object
If amplifier current consumption is reduced for low power applications, then power efficiency improves, but gain bandwidth and slew rate decrease resulting in higher output noise
Solution Approach 1:
The patent carefully selects transistor dimensions and biasing parameters to achieve optimal noise performance at low current consumption. The asymmetric transistor configuration with specific width-to-length ratios maximizes the transconductance efficiency, allowing the amplifier to maintain low output noise while consuming minimal power, making it suitable for battery-powered portable imaging devices
Data Source
AI summary
Various embodiments comprise apparatus, methods, and systems that include an amplification apparatus comprising a first input, a second input, and an output, a first plurality of series-connected transistors including a first transistor having a first channel ratio and a first gate coupled to the first input, and a second plurality of series-connected transistors including a second transistor having a second channel ratio that is greater than the first channel ratio, the second transistor including a second gate coupled to the second input.