Multiclass Power Amplifier With No-Load Modulation for Broadband Efficiency
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Solution Overview
Problem
Conventional Doherty amplifiers experience efficiency reduction due to load modulation effects, which affect power handling and bandwidth, especially when operated at higher peak-to-average power ratios required by modern communication protocols.
Innovation Solution
A multiclass no-load-modulation power amplifier design that includes multiple amplifiers operating in parallel, with a main amplifier and peaking amplifiers configured to operate in different classes, eliminating load modulation by maintaining a consistent impedance for the main amplifier regardless of the peaking amplifiers' state, thereby achieving peak efficiency at deeper back-off powers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional Doherty amplifiers are used with peaking amplifiers that become active at high signal levels, then output power capability is improved, but load modulation occurs causing efficiency reduction and bandwidth limitation
Solution Approach 1:
The amplifier is segmented into multiple independent amplification paths (main amplifier path and peaking amplifier path) that operate in parallel. Each path has its own amplifier operating in a different class, allowing them to handle different signal levels independently without interfering with each other's load conditions.
Solution Approach 2:
An impedance inverter is introduced as an intermediary component between the peaking amplifier and the combining node. This impedance inverter transforms the impedance seen by the main amplifier to remain substantially constant regardless of the peaking amplifier's state, thereby eliminating load modulation effects.
2Power
If conventional Doherty amplifiers are used with peaking amplifiers that become active at high signal levels, then output power capability is improved, but bandwidth is limited due to load modulation effects
Solution Approach 1:
The amplifier is segmented into multiple independent amplification paths (main amplifier path and peaking amplifier path) that operate in parallel. Each path has its own amplifier operating in a different class, allowing them to handle different signal levels independently without interfering with each other's load conditions.
Solution Approach 2:
An impedance inverter is introduced as an intermediary component between the peaking amplifier and the combining node. This impedance inverter transforms the impedance seen by the main amplifier to remain substantially constant regardless of the peaking amplifier's state, thereby eliminating load modulation effects.
3Loss of energy
If multiclass amplifiers operate in parallel with different amplification classes, then efficiency at back-off powers is improved, but device complexity increases
Solution Approach 1:
The amplifier is segmented into multiple independent amplification paths (main amplifier path and peaking amplifier path) that operate in parallel. Each path has its own amplifier operating in a different class, allowing them to handle different signal levels independently without interfering with each other's load conditions.
Solution Approach 2:
An impedance inverter is introduced as an intermediary component between the peaking amplifier and the combining node. This impedance inverter transforms the impedance seen by the main amplifier to remain substantially constant regardless of the peaking amplifier's state, thereby eliminating load modulation effects.
Data Source
AI summary
Apparatus and methods for a multiclass, broadband, no-load-modulation power amplifier are described. The power amplifier (500) may include a main amplifier (532) operating in a first amplification class and a plurality of peaking amplifiers (536, 537, 538) operating in a second amplification class. The main amplifier (532) and peaking amplifiers (536, 537, 538) may operate in parallel on portions of signals derived from an input signal to be amplified. The main amplifier (532) may see no modulation of its load impedance between a fully-on state of the power amplifier (all amplifiers amplifying) and a fully backed-off state (peaking amplifiers idle). By avoiding load modulation, the power amplifier (500) can exhibit improved bandwidth and efficiency compared to conventional Doherty amplifiers.