Power Amplifier Combining Circuit for Isolation and Real Impedance
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Solution Overview
Problem
Current power amplifier configurations, such as those described in Japanese Unexamined Patent Application Publication No. 2012-54874, face limitations in improving output power and linearity, especially with the advent of communication standards like LTE-Advanced that require simultaneous transmission of multiple frequency bands, due to impedance matching issues that result in a substantially imaginary impedance on the load side, hindering amplifier performance.
Innovation Solution
A power amplifier module design that includes a divider circuit, amplifiers, a combining circuit with inductors and capacitors for phase shifting, and a resistance element connected in parallel with a capacitor, which ensures isolation between amplifiers by canceling signal amplitudes and transforming impedance to a real number, enhancing output power and linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single passive element performs impedance matching between amplifier elements and load side, then the configuration is simple, but the impedance on the load side becomes substantially imaginary, limiting amplifier performance and linearity
Solution Approach 1:
The single passive impedance matching element is segmented into multiple components: a first passive element (inductor) connected in series between the amplifier element and combiner, and a second passive element (capacitor) connected in parallel between the combiner and ground. This segmentation allows independent optimization of series and parallel impedance components, enabling the load impedance to be transformed to a real number that maximizes amplifier performance while maintaining circuit simplicity.
2Power
If amplifier elements are used to meet high output power requirements, then output power increases, but isolation between amplifier elements becomes challenging, requiring additional isolation components
Solution Approach 1:
The first passive element (inductor) serves dual functions: it acts as part of the impedance matching network to transform the load impedance to a real number, and simultaneously provides isolation between amplifier elements by being positioned in the signal path between each amplifier element and the combiner. This multi-functionality eliminates the need for separate isolation components, reducing overall device complexity while maintaining high output power 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
The proposed design achieves high output power and linearity by ensuring isolation between amplifiers and optimizing impedance, allowing the power amplifier module to operate effectively across various communication standards, including LTE-Advanced.
Implementation Method 1
a first capacitor connected in parallel to the resistance element. A phase of the third signal from the output terminal of the first amplifier to the output terminal of the second amplifier through the first capacitor is advanced by about 90 degrees
Implementation Method 2
a first inductor connected in series between the output terminal of the first amplifier and the combiner, a second inductor connected in series between the output terminal of the second amplifier and the combiner
Implementation Method 3
a second capacitor having an end connected to the combiner and another end grounded
Implementation Method 4
an isolation resistor that electrically connects output terminals of the set of amplifier elements to each other, and a passive element connected in parallel to the isolation resistor to increase impedance. Thus, if a signal from one path enters the other path in an unbalanced mode, the isolation resistor absorbs power, which ensures isolation between the amplifier elements
Data Source
AI summary
A power amplifier module includes a combining circuit including a combiner. The combining circuit further includes a first inductor connected in series between an output terminal of a first amplifier and the combiner, a second inductor connected in series between an output terminal of a second amplifier and the combiner, and a second capacitor having an end connected to the combiner and another end grounded. A phase of a third signal from the output terminal of the first amplifier to the second amplifier through the combiner is delayed by about 45 degrees in the first inductor and the second capacitor, and is delayed by about 45 degrees in the second inductor and the second capacitor. A phase of the third signal from the output terminal of the first amplifier to the second amplifier through the first capacitor is advanced by about 90 degrees.