Ultra-Wideband Amplifier Biasing Without Impedance Inverters
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Solution Overview
Problem
Designing high efficiency power amplifiers for wide frequency bands is challenging due to the high peak-to-average power ratio (PAPR) of signals, which limits the operational bandwidth and requires bandwidth-limiting circuit elements like impedance inverters, and existing topologies such as Doherty and outphasing amplifiers are restricted by these constraints.
Innovation Solution
A biasing configuration using a current source to bias active devices, allowing output power to increase with increasing load impedance, eliminating the need for bandwidth-limiting circuit elements and enabling efficient operation over a wide bandwidth without impedance inverters, particularly in multi-branch and push-pull amplifier topologies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If Doherty amplifier topology is used to achieve high efficiency for high PAPR signals, then efficiency is improved, but operational bandwidth is limited due to requirement of quasi-open output impedance and impedance inverters
Solution Approach 1:
The patent changes the biasing parameter from constant voltage to constant current, which fundamentally alters the active device's response to load impedance variations. This parameter change enables the device to maintain saturation across varying load conditions, thereby extending operational bandwidth without sacrificing efficiency.
Solution Approach 2:
The patent introduces dynamic load modulation capability through constant current biasing, allowing the active device to adapt its operating point in response to changing load impedance. This dynamic adaptation enables wideband operation while maintaining high efficiency across different signal power levels.
2Ease of operation
If voltage biasing is used to operate active devices, then bias control is simple, but output power decreases with increasing load impedance which limits efficiency
Solution Approach 1:
The patent inverts the conventional biasing approach by using constant current instead of constant voltage. This inversion causes output power to increase with increasing load impedance, which is the opposite behavior of voltage-biased devices, thereby improving efficiency without complicating bias control.
3Loss of energy
If bandwidth-limiting circuit elements like impedance inverters are used, then amplifier topology can achieve high efficiency, but device complexity increases and bandwidth is restricted
Solution Approach 1:
The patent extracts and eliminates the bandwidth-limiting impedance inverter component from the amplifier topology. By using constant current biased active devices, the system achieves high efficiency without requiring these additional complexity-inducing components, thereby simplifying the overall circuit.
4Reliability
If amplifiers operate at average output power much lower than saturated output power to manage high PAPR signals, then signal fidelity is maintained, but overall efficiency is reduced
Solution Approach 1:
The patent enables the active device to maintain continuous saturation operation through constant current biasing, which keeps the device operating at maximum efficiency point continuously. This allows the amplifier to maintain high efficiency even when managing high PAPR signals, rather than operating in a reduced power state.
Data Source
AI summary
An amplifier comprising a current-biased active device, a voltage-biased active device, the voltage-biased active device and the current-biased active device are connected in series, to form a cascade of active devices, and an input terminal and an output terminal, the cascade of active devices connected between the input terminal and the output terminal, having an output terminal for driving a load impedance with an output signal in response to an input signal applied to the input terminal.