Doherty Amplifier Load Admittance Tuning for Broadband Efficiency
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Solution Overview
Problem
Conventional Doherty amplifiers experience efficiency decreases when operating away from a specific frequency due to pure conductance or resistance load impedance, limiting their performance across a broadband frequency range.
Innovation Solution
The Doherty amplifier design expands load admittance and impedance from real to complex values, allowing for a parallel or series connection of output-side two-port networks to maintain efficiency across a broader frequency band by optimizing circuit parameters such as F-parameters and phase differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the load admittance or load impedance is set to a pure conductance or pure resistance, then the efficiency is high at a specific frequency, but the efficiency decreases away from that specific frequency
Solution Approach 1:
The patent changes the load impedance from a pure real value (conductance or resistance) to a complex value with both real and imaginary components. This parameter change allows the amplifier to maintain efficiency across a broader frequency range by compensating for frequency-dependent reactances through the complex impedance matching network.
Solution Approach 2:
The patent introduces dynamic impedance transformation through the use of frequency-dependent reactive elements (inductors and capacitors) in the output matching network. These elements dynamically adjust the load impedance seen by the amplifier to maintain optimal operating conditions across varying frequencies, rather than using a fixed pure resistive load.
2Device complexity
If the Doherty amplifier uses conventional pure resistance load, then the circuit is simple, but the broadband performance is limited
Solution Approach 1:
The patent introduces an intermediate impedance transformation network consisting of reactive elements (inductors and capacitors) between the amplifier output and the load. This intermediary network transforms the pure resistive load into a complex impedance that provides broadband matching, effectively mediating between the simple amplifier core and the broadband performance requirement.
Data Source
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AI summary
A Doherty amplifier (1) of an embodiment includes an input terminal (10), an output terminal (20), a splitter (12), a combiner, a carrier amplifier (14), a peak amplifier (16). The carrier amplifier includes a first input-side two-port network (C1) connected to a first output of the splitter, a first amplifier (C2) connected to an output of the first input-side two-port network, and a first output-side two-port network (C3) connected between an output of the first amplifier and a first input of the combiner. The peak amplifier includes a second input-side two-port network (P1) connected to the second output of the splitter, a second amplifier (P2) connected to an output of the second input-side two-port network, and a second output-side two-port network (P3) connected between an output of the second amplifier and a second input of the combiner. The combiner is a parallel-connected load type having a parallel connection of the output-side two-port network of the carrier amplifier and the output-side two-port network of the peak amplifier for the output terminal at a combining point (18). The load admittance at the combining point is expressed using a complex number.