Dynamic Cascode Biasing in Class AB Amplifiers for Noise Immunity
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Solution Overview
Problem
Class AB amplifiers used in CMOS integrated circuit designs face limitations in maximum gain and are sensitive to power supply noise, which can affect signal quality in digital imaging circuits due to low signal levels.
Innovation Solution
The integration of cascode transistors in the output stage, dynamically biased by differential amplifier stages and current sum branches, enhances open-loop gain and noise immunity by providing a stable voltage signal across the power supply terminals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If class AB amplifier is used in CMOS integrated circuit designs, then it can provide large current during signal transition periods and small current during steady state operation, but the maximum gain is limited and the amplifier output is sensitive to power supply noise
Solution Approach 1:
The output stage is segmented into multiple transistor stages (first output transistor, second output transistor, third output transistor, fourth output transistor) arranged in a push-pull configuration. This segmentation allows each transistor to handle specific portions of the signal waveform, enabling high current output capability during transitions while maintaining stability and reducing noise sensitivity through the distributed structure.
Solution Approach 2:
The invention dynamically changes the operating parameters of the output transistors through differential amplifier stages that control gate voltages. The differential amplifiers adjust the bias conditions and operating points of the output transistors based on input signal conditions, enabling the amplifier to maintain high gain while adapting current output levels to reduce noise sensitivity during steady-state operation.
2Reliability
If differential amplifier stages and current sum branches are used to control output transistors, then gate control signals can be developed, but device complexity increases
Solution Approach 1:
The differential amplifier stages and current sum branches are merged into an integrated control structure where multiple functions are combined in shared circuit elements. The current sum branches serve dual purposes of biasing the output transistors and providing feedback control, while the differential amplifiers simultaneously perform signal differentiation and gain control, reducing overall device complexity despite enhanced control precision.
Solution Approach 2:
The control circuit elements are designed with multi-functionality: the differential amplifier stages not only control gate voltages but also provide impedance matching and signal buffering; the current sum branches simultaneously establish bias currents and provide feedback for stability control. This universality reduces the number of dedicated components needed, managing device complexity while maintaining precise amplifier control.
Data Source
AI summary
An amplifier and method of fabricating and operating it are disclosed in which dynamically biased cascode transistors are provided in an output stage along with output transistors which are dynamically biased by differential control circuits to provide an output signal.