Multiple PWM Power Stage Control for RF Envelope Tracking
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Solution Overview
Problem
High switching frequencies in digital PWM signals for RF power amplifiers lead to low efficiency due to switching losses, particularly in envelope tracking systems for 3G and 4G cellular standards, where the efficiency of RF power amplifiers is reduced.
Innovation Solution
The implementation of multiple digital PWM signals generated from a single PCM input, with digital interpolation filters to upsample the signal to twice the switching frequency times the number of PWM signals, allowing for digital cancellation of switching frequencies and intermodulation, thereby reducing switching frequency without compromising performance, and using passive L-C low pass filters to filter out high-frequency content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the switching frequency of PWM signals is increased to match higher RF signal bandwidth, then the RF power amplifier can support newer standards, but the power conversion efficiency decreases due to switching losses
Solution Approach 1:
The patent divides the single high-frequency PWM signal into multiple lower-frequency PWM signals that drive separate power stages. By segmenting the power amplification function across multiple stages operating at lower switching frequencies, the overall system achieves the required high bandwidth performance while reducing individual stage switching losses and improving efficiency.
2Loss of energy
If multiple power stages are used to reduce switching frequency, then efficiency improves, but current sharing among stages becomes complex requiring costly current sensing
Solution Approach 1:
The patent uses identical copies of the same power stage circuitry multiple times, where each stage has the same characteristics and switching frequency. This symmetry allows the stages to naturally share current equally without requiring complex current sensing or balancing circuits, as each identical stage operates under the same conditions and contributes equally to the total output.
3Adaptability or versatility
If digital circuitry is used to create PWM signals for wide bandwidth RF signals, then the system can support higher bandwidth standards, but switching losses increase at the required high switching frequencies
Solution Approach 1:
The patent segments the high-bandwidth signal processing function across multiple digital PWM channels, each operating at a lower switching frequency. This allows the system to maintain digital control flexibility and bandwidth support while each individual power stage operates at a more efficient lower frequency, resolving the contradiction between bandwidth capability and switching efficiency.
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
This approach enhances the efficiency of RF power amplifiers by reducing switching frequency, maintaining performance, and allowing for easy filtering of high-frequency components, thus improving power conversion efficiency.
Implementation Method 1
passive L-C low pass filters
Data Source
AI summary
A DC power stage provides a power output that tracks a PCM signal input. A mapping unit generates an integer number of N digital PWM signals each switched at a same switching frequency by switching states of the PWM signals one at a time based on a level of the PCM signal input. An imbalance correction unit adjusts a duty ratio of the PWM signals relative to one another based on differentially accumulating errors among the PWM signals to prevent divergence of PWM signals. N corresponding switches therefrom switch power from a DC power source. N inductances in parallel produce a combined signal that is low pass filtered to provide the power output. Switching is between only those state combinations where the switching frequency is cancelled in the combined signal. The switching frequency is a sampling frequency of the PCM signal input divided by a product of 2 times N.