RF Power Combiner Circuit for Low EVM at High Output Power
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Solution Overview
Problem
Conventional RF power amplifiers struggle to maintain linearity at high output power levels, with Class A amplifiers meeting EVM floor requirements only at lower power levels and Class AB/B amplifiers failing to meet these requirements at low to mid power levels.
Innovation Solution
The RF power combining amplifier circuit selectively activates Class A amplifiers for small voltage signals and Class B or C amplifiers for high output power levels, with individual output matching networks to maintain low error vector magnitude (EVM) floors and high output power levels by combining amplifier outputs in parallel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Class A amplifiers are used, then linearity and EVM floor requirements are met at lower power levels, but output power capability is limited
Solution Approach 1:
The power amplifier is divided into multiple parallel amplifier paths (Class A, Class AB, and Class B amplifiers) that operate in different power ranges. Each amplifier class is optimized for specific power levels, with Class A handling low power for linearity, Class AB for medium power, and Class B for high power, thereby resolving the contradiction between maintaining EVM floor and achieving high output power.
Solution Approach 2:
The system dynamically selects and switches between different amplifier classes based on the instantaneous power level requirements. The power combining circuit actively manages which amplifiers are engaged at any given time, transitioning from Class A at low power to Class AB and Class B at higher powers, thus adapting the linearity characteristics to match the operating conditions.
2Power
If Class AB/B amplifiers are used, then high output power levels are achieved, but EVM floor requirements are not met at low to mid power levels
Solution Approach 1:
The power amplifier system segments the power range into distinct operating zones, each handled by a specific amplifier class optimized for that zone. Class A amplifiers handle the low to mid power range where linearity is critical, while Class AB and Class B amplifiers handle the high power range where maximum output is prioritized, eliminating the EVM degradation that occurs in conventional single-class designs at low powers.
Solution Approach 2:
The power combining circuit acts as an intermediary that merges the outputs of multiple amplifier classes with different linearity characteristics. By combining the low-power Class A output with the high-power Class AB/B outputs, the system achieves both high overall power capability and maintained EVM floor across the entire power range.
3Power
If multiple power amplifiers are combined with a transformer, then output power is increased, but the system complexity and power loss increase
Solution Approach 1:
The patent replaces the conventional transformer-based power combining mechanism with a direct parallel combining architecture using power combining circuits. This substitution eliminates the need for bulky transformers and associated impedance matching networks, reducing system complexity, size, and power losses while maintaining the ability to combine multiple amplifier outputs effectively.
Data Source
AI summary
A radio frequency (RF) power combining amplifier circuit has a circuit input and a circuit output. A first amplifier is connected to the circuit input and to a first bias input. A first output matching network is connected to an output of the first amplifier and to the circuit output. A second amplifier is connected to the circuit input and to a second bias input. A second output matching network is connected to an output of the second amplifier, and to the circuit output. A voltage level of an input signal applied to the circuit input, together with the respective first bias input and the second bias input, selectively activates the first amplifier and the second amplifier.