Doherty Amplifier Peaking-Path Compensation for Wider Bandwidth
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Solution Overview
Problem
Doherty amplifiers face challenges in achieving a wider bandwidth due to frequency dependence of the 90-degree line, leading to a larger and more complex circuit design, and limitations in handling wider input signal frequency bandwidths.
Innovation Solution
Incorporating a compensation circuit between the peaking amplifier and the combiner, which causes an open impedance within the used frequency range and compensates for frequency dependence, ensuring the impedance seen from the output end toward the combiner is adjusted to achieve 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 compensate for frequency dependence, then the bandwidth is improved, but the device complexity and size increase due to requiring a control mechanism for selecting lines
Solution Approach 1:
The patent combines the frequency dependence compensation function into the existing 90-degree line structure by adding a compensation circuit at its output. This merges the compensation function with the existing signal path rather than requiring separate selectable lines, thereby reducing device complexity while maintaining bandwidth improvement.
Solution Approach 2:
The compensation circuit is designed to handle multiple frequency ranges simultaneously through a universal structure that provides frequency dependence compensation across the entire operating bandwidth. This eliminates the need for multiple specialized lines with different electrical lengths, reducing both device complexity and size while maintaining adaptability.
2Manufacturing precision
If a control mechanism is added to detect frequency and select appropriate lines, then the electrical length accuracy is improved, but the ease of manufacture and device simplicity deteriorate
Solution Approach 1:
The compensation circuit operates autonomously without requiring external frequency detection or control mechanisms. It automatically compensates for frequency dependence through its inherent circuit design, eliminating the need for complex control systems while maintaining electrical length accuracy across different frequencies.
Solution Approach 2:
The compensation circuit acts as an intermediary element that passively compensates for frequency effects without requiring active control. By placing this compensation element in the signal path, the system achieves accurate electrical length without the complexity of frequency detection and switching mechanisms.
3Productivity
If the 90-degree line is used for load modulation at the carrier amplifier output, then operational efficiency during back-off is improved, but frequency dependence causes the electrical length to deviate from 90 degrees, narrowing the bandwidth
Solution Approach 1:
The patent changes the electrical parameters of the 90-degree line by adding a compensation circuit that modifies the impedance characteristics. This compensation adjusts the electrical length to remain close to 90 degrees across a wider frequency range, thereby maintaining operational efficiency during back-off while expanding the usable bandwidth.
Data Source
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.