Multimode RF Power Amplifier Biasing Without a High-Current LDO
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Solution Overview
Problem
Conventional multimode power amplifiers face challenges in efficiently switching between linear and saturated modes, leading to increased component count, compromised noise performance, and reduced efficiency due to complex circuit requirements and high current low drop out regulators.
Innovation Solution
A multimode power amplifier design that maintains a low impedance voltage bias for both linear and saturated modes, using an adjustable supply voltage for driver stages and a fixed supply voltage for the output stage, eliminating the need for a large LDO and enhancing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a switched bias technique is used to provide low impedance voltage bias for linear mode and high impedance voltage bias for saturated mode, then the amplifier can operate in both modes, but the circuit complexity increases and noise performance deteriorates
Solution Approach 1:
The amplifier is divided into driver stages and output stage, with different biasing arrangements for each segment. The driver stages use switched bias to operate in both linear and saturated modes, while the output stage maintains a fixed low impedance voltage bias throughout, eliminating the need for bias switching in the output path and reducing overall circuit complexity.
Solution Approach 2:
The output stage is designed to universally operate in both linear and saturated modes with a fixed low impedance voltage bias, eliminating the need for mode-specific bias switching circuitry. This multi-functional approach allows the output stage to handle both operating modes without requiring complex switching mechanisms.
2Adaptability or versatility
If a high current low drop out regulator is used to regulate supply voltage for saturated mode operation, then output power can be controlled in saturated mode, but voltage drop increases and efficiency decreases
Solution Approach 1:
The power amplifier is segmented into driver stages and output stage with separate power supply arrangements. The driver stages use a regulated supply voltage (VREG) that can be adjusted for saturated mode operation, while the output stage uses a fixed supply voltage, eliminating the need for a high current LDO and reducing voltage drop and energy loss.
Solution Approach 2:
The supply voltage to the driver stages (VREG) is dynamically changed based on operating mode. In saturated mode, VREG is regulated to control output power, while in linear mode, it operates with a fixed supply voltage. This parameter change approach allows efficient saturated mode operation without requiring a high current LDO for the entire amplifier.
Data Source
AI summary
According to an exemplary embodiment, a multimode power amplifier configured to receive an RF input signal and provide an RF output signal in linear and saturated operating modes includes an output stage configured to receive a fixed supply voltage and to provide the RF output signal. The multimode power amplifier further includes at least one driver stage coupled to the output stage, where the at least one driver stage is configured to receive the RF input signal and an adjustable supply voltage. The adjustable supply voltage controls an RF output power of the RF output signal when the multimode power amplifier is in the saturated operating mode. The at least one driver and the output stage are each biased by a low impedance voltage in the linear and saturated operating modes. The adjustable supply voltage can be controlled by a fixed control voltage in the linear operating mode.