Doherty Amplifier Load Modulation Using Complex Impedance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Doherty amplifiers experience efficiency drops when operating away from specific frequencies due to pure conductance or resistance load impedance, limiting their performance in systems requiring high efficiency across a range of frequencies.
Innovation Solution
The Doherty amplifier design expands load admittance and impedance from real to complex values, allowing for a broader design space and increased design freedom, enabling efficient operation across a broader frequency band by optimizing circuit parameters and incorporating complex admittances and impedances in the combiner and output networks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the load admittance or load impedance is set to pure conductance or pure resistance, then high efficiency is achieved at a specific frequency, but efficiency decreases away from that specific frequency
Solution Approach 1:
The patent changes the load impedance from pure real values (conductance or resistance) to complex values by introducing reactive components. This parameter change allows the amplifier to maintain efficiency across a broader frequency range by compensating for frequency-dependent impedance variations through the imaginary component of the complex load impedance.
Solution Approach 2:
The patent implements dynamic impedance matching by making the load impedance complex rather than fixed and real. The complex load impedance can adapt to frequency changes, allowing the amplifier to maintain optimal efficiency across varying operating conditions and frequencies, rather than being optimized for a single fixed frequency.
2Device complexity
If conventional Doherty amplifier designs with real-axis load impedances are used, then circuit design is simplified, but frequency bandwidth is limited
Solution Approach 1:
The patent extends the load impedance from the real axis to the complex plane by introducing reactive elements. This allows designers to independently optimize both the real (resistive) and imaginary (reactive) components of the load impedance, providing additional degrees of freedom to broaden the operating frequency band while managing circuit complexity through systematic design methods.
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
A Doherty amplifier (1) includes an input terminal (10), an output terminal (20), a splitter (12), a combiner (22), a carrier amplifier (14), a peak amplifier (16). The splitter is connected to the input terminal, the splitter having first and second outputs. The combiner is connected to the output terminal, the combiner having first and second inputs. The carrier amplifier includes a first input-side two-port network connected to the first output of the splitter, a first amplifier connected to an output of the first input-side two-port network, and a first output-side two-port network connected between an output of the first amplifier and the first input of the combiner. The peak amplifier includes a second input-side two-port network connected to the second output of the splitter, a second amplifier connected to the output of the second input-side two-port network, and a second output-side two-port network connected between an output of the second amplifier and the second input of the combiner. The combiner is a series-connected load type having a series connection of the output-side two-port network of the carrier amplifier with the output-side two-port network of the peak amplifier and the output terminal. The load impedance is expressed using a complex number.