Doherty Amplifier Compensation Circuit for Wider Bandwidth
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Solution Overview
Problem
Doherty amplifiers face challenges in achieving a wider bandwidth due to frequency dependence issues, leading to a larger and more complex circuit design, particularly when dealing with input signals having a wider frequency bandwidth than the individual lines can cover.
Innovation Solution
A compensation circuit with multiple lines of 180 degrees electrical length, having different characteristic impedances, is introduced between the peaking amplifier and the combiner to compensate for impedance frequency dependence, ensuring the impedance remains open within the used frequency range and adjusts between capacitive and inductive regions, thereby achieving a wider bandwidth without increasing circuit complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple lines with different electrical lengths are provided at the output of the carrier amplifier to cover wider bandwidth, then the bandwidth is improved, but the circuit size and complexity increase due to detection and control mechanisms
Solution Approach 1:
The invention divides the peaking amplifier output path into multiple parallel lines (first line, second line, etc.), each with different electrical lengths. This segmentation allows different frequency components to be routed through appropriate lines, achieving wide bandwidth coverage without requiring complex detection and control mechanisms. The simple parallel structure inherently provides frequency-dependent impedance transformation.
Solution Approach 2:
The multiple lines at the peaking amplifier output serve multiple functions simultaneously: they provide frequency-dependent impedance transformation, enable wide bandwidth operation, and eliminate the need for separate detection and control circuits. This multi-functionality resolves the contradiction by achieving bandwidth improvement without increasing overall circuit complexity.
2Device complexity
If a single line with fixed electrical length is used at the output of the carrier amplifier, then the circuit remains simple, but the bandwidth is limited due to frequency dependence
Solution Approach 1:
Instead of using a single fixed line, the invention segments the output path into multiple parallel lines with different electrical lengths. This simple segmentation approach maintains circuit simplicity while enabling wide bandwidth operation, as each line naturally handles different frequency ranges without requiring active control.
3Adaptability or versatility
If the electrical length of the 90-degree line deviates from 90 degrees due to frequency dependence, then the operation bandwidth becomes narrow, but adding multiple lines increases circuit complexity
Solution Approach 1:
The invention segments the peaking amplifier output into multiple parallel lines with different electrical lengths. This segmentation provides frequency-dependent impedance transformation that compensates for the 90-degree line's electrical length deviation, achieving wide operation bandwidth without increasing circuit complexity through simple parallel connection.
Solution Approach 2:
The invention changes the electrical length parameter of the peaking amplifier output lines to create a set of lines with different electrical lengths. This parameter variation enables frequency-dependent impedance transformation that compensates for the 90-degree line's frequency dependence, achieving wide bandwidth without complex control mechanisms.
Data Source
Figure 1~2
Figure 3~4
Figure 5~7
AI summary
In a Doherty amplifier including a carrier amplifier (6) and a peaking amplifier (8) connected in parallel with each other, a compensation circuit (9) for causing an impedance seen from an output end (9a) of the compensation circuit (9) toward the peaking amplifier (8) to be open within a used frequency range and compensating for frequency dependence of an impedance seen from an output of a combiner (10) toward the combiner (10) in a state in which the peaking amplifier (8) is not operating is arranged between the peaking amplifier (8) and the combiner (10). This achieves a wider bandwidth without making the circuit larger in size and more complicated.