Multimode Power Amplifier Biasing for Linear and Saturated Modes
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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 low drop out regulator 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 support both linear and saturated modes, but the circuit complexity increases and noise performance deteriorates
Solution Approach 1:
The patent applies dynamics by making the bias impedance adjustable rather than fixed. A control voltage signal dynamically adjusts the impedance of the voltage bias circuit between low impedance (for linear mode) and high impedance (for saturated mode), allowing the amplifier to adapt to different operating modes without requiring complex switching circuits. This resolves the contradiction by enabling mode adaptability while keeping the circuit relatively simple through continuous adjustment rather than discrete switching.
Solution Approach 2:
The patent changes the impedance parameter of the voltage bias circuit based on the desired operating mode. By varying the impedance value (from low to high) according to the mode selection signal, the amplifier can operate in either linear or saturated mode. This parameter change approach eliminates the need for complex bias switching circuits while maintaining both operating modes, thus resolving the technical contradiction between adaptability and circuit complexity.
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, but voltage drop increases and efficiency decreases
Solution Approach 1:
The patent extracts the voltage regulation function from a separate high current LDO regulator and integrates it into the bias circuit itself. The bias circuit now serves dual purposes: providing voltage bias and regulating supply voltage when needed. This eliminates the need for a dedicated high current LDO that would cause voltage drop and efficiency loss, while still enabling output power control in saturated mode through the same bias circuitry.
Solution Approach 2:
The voltage bias circuit is designed to perform multiple functions: it provides low impedance bias for linear mode operation, high impedance bias for saturated mode operation, and also regulates the supply voltage to the output stage. By making the bias circuit multi-functional, the patent eliminates the need for separate high current LDO regulators, thereby reducing voltage drop and improving efficiency while maintaining output power control capability.
3Adaptability or versatility
If bias switching is implemented between linear and saturated modes, then mode transition is possible, but slew rate limits and noise performance are compromised
Solution Approach 1:
The patent uses dynamic adjustment of bias impedance instead of abrupt switching. A control voltage smoothly transitions the bias circuit between low impedance (linear mode) and high impedance (saturated mode) states. This dynamic approach avoids the slew rate limitations and noise spikes associated with hard switching, enabling mode transitions while maintaining good noise performance and reliability.
Data Source
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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.