PA Voltage Regulator With Selective Feedback for Low Memory Effects
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Solution Overview
Problem
Conventional power amplifiers (PAs) face significant memory effects and error vector magnitude (EVM) limitations due to wide output voltage ranges and varying current demands, especially when processing non-constant envelope signals, which are exacerbated by slow regulator settling behavior and complex digital compensation solutions.
Innovation Solution
A voltage regulator with an operational amplifier and replica device provides a regulated voltage to a power amplifier, using a feedback system with selectively enabled feedback devices based on output power levels and modulation schemes, eliminating the need for dynamic digital pre-distortion and reducing memory effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a linear regulator is used to limit the voltage to protect transistors, then transistor reliability is improved, but memory effects increase and EVM performance deteriorates
Solution Approach 1:
The regulator transitions from a static design to a dynamic one by selectively enabling feedback devices based on output power level. The controller adjusts the number of active feedback devices in real-time, allowing the regulator to adapt its bandwidth and settling behavior to match the PA's operating conditions, thereby reducing memory effects while maintaining transistor protection
Solution Approach 2:
The system changes the operational parameters of the regulator by varying the number of enabled feedback devices according to the output power level. This parameter adjustment optimizes the feedback loop characteristics dynamically, improving EVM performance across different power levels while maintaining voltage regulation for transistor protection
2Stability of the object's composition
If conventional regulator topologies are used to provide voltage regulation, then voltage stability is improved, but memory effects significantly increase and limit achievable EVM
Solution Approach 1:
The regulator employs dynamic control by selectively enabling feedback devices based on the PA's output power level. This dynamic adjustment optimizes the feedback loop bandwidth and settling time to match the operating conditions, reducing memory effects while maintaining voltage stability for transistor protection
Solution Approach 2:
The system enhances the feedback mechanism by selectively enabling feedback devices based on output power level. The controller monitors the PA's operating conditions and adjusts the feedback loop configuration accordingly, optimizing the balance between voltage stability and memory effect reduction across different power levels
3Manufacturing precision
If digital compensation is used to correct memory effects, then EVM performance is partially improved, but system complexity increases significantly
Solution Approach 1:
The invention converts the harmful memory effects into a beneficial control mechanism. By selectively enabling feedback devices based on output power level, the system uses the regulator's inherent characteristics to reduce memory effects, turning what was previously a problem requiring complex digital compensation into a feature that simplifies the overall system
Solution Approach 2:
The system extracts and eliminates the need for complex digital compensation by implementing analog control through selective feedback device enabling. This approach removes the harmful memory effects at the source through analog circuitry rather than requiring subsequent digital correction, thereby reducing overall system complexity
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 solution achieves reduced memory effects and improved EVM performance, enabling power amplifiers to operate with minimal complexity and achieve an EVM of at least -45 dB across a wide power control range without dynamic digital compensation.
Implementation Method 1
an operational amplifier (opamp) to amplify a difference between a reference voltage and a feedback voltage and output a bias signal based on the difference
Implementation Method 2
a replica device coupled to the opamp, the replica device having a gate terminal to receive the bias signal
Implementation Method 3
an output stage coupled to the replica device and to output a regulated voltage, the output stage comprising a pass device and a plurality of feedback devices coupled to the pass device
Data Source
AI summary
In one example, an apparatus includes: an operational amplifier (opamp) to amplify a difference between a reference voltage and a feedback voltage and output a bias signal based on the difference; a replica device coupled to the opamp, the replica device having a gate terminal to receive the bias signal; and an output stage coupled to the replica device and to output a regulated voltage, the output stage having a pass device and a plurality of feedback devices coupled to the pass device. A selected number of the plurality of feedback devices can be enabled based at least in part on an output power level of a power amplifier that is to receive the regulated voltage.