Doherty Amplifier Parasitic Capacitance Area Reduction
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Solution Overview
Problem
Existing Doherty power amplifiers have a large area due to the requirement of output matching circuits and λ/4 transmission lines, which limits their compactness and efficiency.
Innovation Solution
The use of parasitic capacitors (Cds) between the drains and sources of power transistors and a printed circuit board (PCB) transmission line forms a π-type network to implement a 90-degree impedance conversion function, eliminating the need for an output matching circuit and reducing the length of transmission lines, thereby minimizing the amplifier's area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If output matching circuits and λ/4 transmission lines are used in a typical Doherty power amplifier, then impedance conversion and power synthesis functions are achieved, but the amplifier area becomes relatively large
Solution Approach 1:
The patent combines the output matching circuit and the λ/4 transmission line into a single integrated structure. The λ/4 transmission line is configured to simultaneously perform impedance conversion and act as the output matching circuit, eliminating the need for separate matching components. This merging reduces the overall amplifier area while maintaining the required impedance conversion function from 50 ohms to the optimal impedance for power synthesis.
Solution Approach 2:
The λ/4 transmission line is designed to serve multiple functions: it acts as an impedance converter, functions as the output matching circuit, and facilitates power synthesis between the carrier and peak amplification paths. By making the transmission line multi-functional, the patent eliminates redundant components and reduces the amplifier footprint.
2Reliability
If separate output matching circuits and transmission lines are implemented, then proper impedance matching is achieved, but device complexity increases
Solution Approach 1:
The patent merges the output matching circuit functionality into the λ/4 transmission line structure. Instead of having separate matching circuits for each power transistor, the transmission line provides centralized impedance transformation that simplifies the overall circuit architecture while maintaining proper impedance matching for both the carrier and peak paths.
Solution Approach 2:
The patent extracts the impedance matching function from separate dedicated circuits and integrates it into the transmission line structure. This extraction and integration approach reduces the number of discrete components and simplifies the circuit design while preserving the essential impedance matching capability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for a more compact Doherty power amplifier design by directly connecting power transistors and reducing the length of transmission lines, achieving efficient impedance conversion without the need for a separate output matching circuit, thus minimizing the overall area and enhancing performance.
Implementation Method 1
The use of parasitic capacitors (Cds) between the drains and sources of power transistors and a printed circuit board (PCB) transmission line forms a π-type network to implement a 90-degree impedance conversion function
Data Source
Figure 1~3a
Figure 3b
Figure 4~5
AI summary
Embodiments of the present invention relate to a Doherty power amplifier that includes a main power amplification circuit, an auxiliary power amplification circuit, a connection circuit, and an impedance conversion circuit, where an output end of the main power amplification circuit and an output end of the auxiliary power amplification circuit are connected to two ends of the connection circuit separately by using bonding wires, the output end of the auxiliary power amplification circuit is further connected to one end of the impedance conversion circuit by using a bonding wire, and the other end of the impedance conversion circuit is connected to an output load. In the embodiments of the present invention, an impedance conversion circuit is formed by directly connecting parasitic capacitors Cds between drains and sources of dies in two power transistors and a PCB, so that an output matching circuit in an existing Doherty power amplifier can be removed, thereby achieving an effect of reducing an area of the Doherty power amplifier.