Class AB RF Amplifier Topology With Transformers for Linear Power
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Solution Overview
Problem
The prior art class AB RF amplifier topology is not suitable for producing high output power while meeting linearity requirements, as it has poor EVM characteristics and efficiency, making it less competitive compared to common-emitter HBT GaAs RF amplifiers.
Innovation Solution
The proposed RF amplifier system includes matching networks with input and output transformers, a multi-stage amplifier configuration, and specific transformer ratios to achieve impedance and phase matching, along with Gm boosting and harmonic rejection, to enhance current and voltage gain, and protect transistors from damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the prior art class AB RF amplifier topology is used, then the circuit structure is simple, but the output power is limited and linearity is poor
Solution Approach 1:
The amplifier is divided into multiple stages including input matching network, input transformer, first amplifier stage, output transformer, and output matching network. Each stage performs a specific function to progressively build up the signal while maintaining linearity and achieving high output power.
Solution Approach 2:
Transformers are introduced as intermediary components between the amplifier stages and matching networks. The input transformer provides current gain and impedance transformation, while the output transformer provides voltage gain and impedance matching, enabling the amplifier to deliver high power to the antenna while maintaining linearity.
2Device complexity
If the prior art class AB RF amplifier topology is used, then the circuit configuration is simple, but the efficiency is poor
Solution Approach 1:
The amplifier operates in class AB mode, which is a parameter change from traditional class A or class C operation. This allows the amplifier to achieve better efficiency than class A while maintaining linearity, by biasing the transistors to conduct for more than half but less than the full cycle of the input signal.
3Power
If high output power is achieved, then the amplifier can meet communication standards, but linearity requirements become difficult to satisfy
Solution Approach 1:
The transformers act as intermediaries that provide impedance transformation and signal coupling while maintaining signal integrity. The input transformer with turns ratio N1:N2 provides current gain, and the output transformer with turns ratio N3:N4 provides voltage gain, enabling high power output while maintaining linearity through proper impedance matching.
Solution Approach 2:
The amplifier uses class AB operation mode, which is a parameter change from traditional operating modes. This allows the amplifier to maintain linearity at high output power levels by biasing the transistors to conduct for more than half but less than the full cycle of the input signal, achieving a balance between power and linearity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design delivers high output power with improved linearity, efficiency, and broadband characteristics, effectively addressing the limitations of the prior art by providing a competitive solution for modern communication standards.
Implementation Method 1
The input transformer configured to receive the matching network output signal and output an input transformer output
Implementation Method 2
An output transformer configured to receive the amplified signal and output an output transformer output signal
Data Source
AI summary
An amplifier system comprising an input matching network configured to receive an input signal from a signal source. The input matching network is configured to impedance match between the amplifier system and the signal source. An input transformer is configured to receive the impedance matched input signal and perform voltage step down and current step up. An amplifier is configured to receive and amplify an output signal from the input transformer to generate an amplified signal. A low winding ratio output transformer provides isolation between an antenna and amplifier. An output matching network is configured to impedance match to an antenna and provide voltage step up. The input transformer may have a ratio of 2N:N, such as 2:1 ratio. At least one center tap of the input transformer may connect to a bias voltage. The amplifier system may be configured for operation in the radio frequency band.