Doherty Amplifier Balun Layout for Common Bias Supply
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Solution Overview
Problem
Doherty amplifiers using lumped parameter baluns face challenges in applying a common bias voltage due to the presence of a series-connected capacitor, which impedes direct current connection between the carrier and peak amplifiers.
Innovation Solution
A Doherty amplifier design that incorporates a balun with lumped parameter elements, featuring a path between the amplifiers that is DC-connected without a series capacitor, utilizing inductors in series and shunt connections to facilitate bias voltage supply to both amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a lumped parameter balun is used as a combiner in a Doherty amplifier, then the amplifier size is reduced compared to a quarter wavelength transmission line combiner, but a capacitor must be connected in series in the path between amplifiers which prevents common bias voltage application
Solution Approach 1:
The patent extracts and removes the series capacitor from the signal path between the carrier amplifier and peak amplifier. By eliminating this capacitor, the DC connection is restored, allowing a common bias voltage to be applied to both amplifiers while maintaining the compact lumped parameter balun structure.
Solution Approach 2:
The patent creates a universal bias voltage path that serves both amplifiers simultaneously. The bias voltage supply is designed to provide DC connection to both the carrier amplifier and peak amplifier through a shared path, making the biasing system multi-functional and eliminating the need for separate bias circuits.
2Reliability
If a series capacitor is used in the path between carrier amplifier and peak amplifier with a lumped parameter balun, then the balun can function as a combiner, but the capacitor acts as a DC cut capacitor preventing common bias voltage application
Solution Approach 1:
The series capacitor that was preventing DC connection is removed from the path between amplifiers. This extraction eliminates the DC block while preserving the AC combiner function of the balun, simplifying the overall circuit configuration.
Solution Approach 2:
The patent introduces a new bias voltage supply path that acts as an intermediary, providing DC connection between the amplifiers without interfering with the AC signal combining function of the balun. This intermediary path resolves the conflict between DC biasing requirements and AC signal isolation.
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
Enables efficient operation of the Doherty amplifier by allowing a single bias circuit to supply voltage to both amplifiers, reducing the amplifier's size and maintaining performance by eliminating the impact of capacitors on impedance matching.
Implementation Method 1
the balun includes inductors connected in series in the path, and a capacitor shunt connected to the path
Implementation Method 2
the balun includes a first inductor connected at one end thereof to the first node and connected at the other end thereof to the third node, a capacitor shunt connected between the first node and the first inductor
Data Source
AI summary
A Doherty amplifier includes a divider configured to divide an input signal into two signals, a first amplifier configured to amplify one of the two signals and output the amplified signal to a first node, a second amplifier configured to amplify the other of the two signals and output the amplified signal to a second node, a balun including lumped parameter elements and configured to output a signal obtained by combining the signal output from the first amplifier with the signal output from the second amplifier to a third node, and a path configured to DC-connect the first node to the second node, with the third node therebetween.