Cascode Power Amplifier Feedback for Impedance Matching
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Solution Overview
Problem
Multi-stage stacked power amplifiers in RF devices face performance degradation due to impedance mismatches between amplifier stages, particularly in cascode configurations, leading to issues like output return loss and voltage standing wave ratio (VSWR) performance, which worsen with increasing stack heights.
Innovation Solution
A radio frequency (RF) circuit arrangement with a multi-stage power amplifier featuring a cascaded configuration of a final cascode amplifier and a driver amplifier, connected via a coupling network and a feedback network between their output and input nodes, respectively, to reduce impedance mismatch and improve performance by tuning the load impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a multi-stage arrangement with cascode amplifiers is used to achieve required power output, then power output is improved, but impedance mismatch occurs affecting output return loss and VSWR performance
Solution Approach 1:
A feedback network is introduced that couples the output node of the final amplifier back to the input node of the final amplifier. This feedback mechanism dynamically adjusts the operating conditions to maintain proper impedance matching across different power output levels, thereby resolving the contradiction between achieving high power output and maintaining reliable impedance match.
Solution Approach 2:
The invention changes the operating parameters of the cascode amplifier stages by introducing the feedback network, which modifies the effective output impedance. This parameter adjustment allows the amplifier to maintain optimal impedance matching while operating at the required power output levels, eliminating the traditional trade-off between power and impedance match.
2Strength
If stacked transistors are used in cascode configuration, then voltage handling capability is improved, but output impedance changes causing impedance mismatch
Solution Approach 1:
The feedback network compensates for the output impedance changes introduced by the stacked transistor configuration. By feeding back a portion of the output signal to the input, the system dynamically adjusts to maintain consistent impedance characteristics regardless of the voltage handling requirements imposed by the cascode structure.
3Power
If multi-stage arrangement is used to achieve required power output, then power output is improved, but output return loss performance deteriorates
Solution Approach 1:
The feedback network directly addresses the output return loss issue by adjusting the effective output impedance through the feedback path. This allows the multi-stage amplifier to maintain low return loss across the operating range while achieving the required power output levels.
4Power
If multi-stage arrangement is used to achieve required power output, then power output is improved, but voltage standing wave ratio performance deteriorates
Solution Approach 1:
The feedback mechanism improves VSWR performance by dynamically adjusting the output impedance to match the load impedance across different power levels. This reduces standing wave formation and improves overall system efficiency while maintaining the required power output.
Data Source
AI summary
Methods and devices for providing a feedback network in a multi-stage power amplifier are described. According to one aspect, a final amplifier of the multi-stage power amplifier is a cascode amplifier. The feedback network is placed between an output of the final amplifier and an output of a driver amplifier. The feedback network can decrease a mismatch between the output impedance of the final amplifier and a load presented to the final amplifier. In addition, the feedback network can change a load presented to the driver amplifier and thereby allow the transfer functions of each stage to be tuned so that the overall transfer function of the multi-stage amplifier becomes more linear.