Cross-Coupled Source Degeneration for Rail-to-Rail Class-AB Amplifiers
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Solution Overview
Problem
Existing wireless communication network amplifiers, particularly those using class-AB amplifiers, face challenges in biasing transistors due to low voltage thresholds, leading to increased power consumption and reduced dynamic range, especially when coupled with high-gain-bandwidth first amplification stages.
Innovation Solution
Implementing a source degeneration circuit with cross-coupled transistors and resistors to increase the voltage threshold headroom of class-AB amplifiers, allowing proper biasing while maintaining rail-to-rail voltage swing and improving common-mode rejection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If class-AB amplifiers are used with low voltage threshold transistors to achieve high gain-bandwidth product, then amplification performance is improved, but power consumption increases and dynamic range is reduced
Solution Approach 1:
The patent changes the voltage threshold parameter of the transistors by introducing source degeneration circuits. The source degeneration increases the effective voltage threshold headroom, allowing the use of low voltage threshold transistors without the penalty of increased power consumption. This parameter change resolves the contradiction by decoupling the relationship between voltage threshold and power consumption.
2Productivity
If class-AB amplifiers are used with low voltage threshold transistors to achieve high gain-bandwidth product, then amplification performance is improved, but dynamic range is reduced
Solution Approach 1:
The source degeneration circuit changes the voltage threshold parameter to increase voltage headroom. This parameter change allows the amplifier to operate with larger voltage swings, thereby expanding the dynamic range while maintaining high amplification performance. The cross-coupled transistors further adjust the operating point to optimize dynamic range.
Solution Approach 2:
The source degeneration circuit acts as an intermediary between the low voltage threshold transistors and the power supply. It mediates the voltage levels to provide sufficient headroom for large signal operation, thus preserving dynamic range while enabling the use of high-performance low threshold transistors.
3Use of energy by moving object
If source degeneration circuit with cross-coupled transistors is implemented to increase voltage threshold headroom, then proper biasing is achieved and power consumption is reduced, but device complexity increases
Solution Approach 1:
The patent merges the biasing function and the voltage threshold adjustment function into a single source degeneration circuit with cross-coupled transistors. This combination achieves multiple objectives (proper biasing, voltage headroom increase, power consumption reduction) simultaneously, thereby justifying the increased device complexity through functional integration and performance improvement.
Data Source
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AI summary
Certain aspects of the present disclosure generally relate to using cross-coupled transistors for source degeneration of an amplification stage. For example, the amplification stage generally includes a differential amplifier comprising transistors, cross-coupled transistors coupled to the differential amplifier, and an impedance coupled between drains of the cross-coupled transistors. In certain aspects, the differential amplifier comprises a push-pull amplifier, and the transistors of the push-pull amplifier comprise cascode-connected transistors.