Envelope Tracking Supply Modulator with Slew Rate Redistribution
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Solution Overview
Problem
Existing envelope tracking systems for RF power amplifiers in wireless communication units face inefficiencies, particularly in supply modulation, leading to reduced transmitter efficiency and increased heat dissipation, especially under varying load conditions and for complex modulation schemes with high peak-to-average power ratio.
Innovation Solution
The implementation of a slew rate module that redistributes the maximum slew rate across input samples of an envelope signal to avoid step inputs to the supply modulator, thereby reducing out-of-band emissions and improving supply modulation efficiency, which is achieved through a combination of DC-DC converters and linear amplifiers in a hybrid supply modulator design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If envelope tracking is used to improve power amplifier efficiency, then transmitter efficiency is improved, but out-of-band emissions increase due to step inputs in supply modulation
Solution Approach 1:
The slew rate module pre-processes the envelope signal before it reaches the supply modulator, redistributing maximum slew rate across input samples to prevent step inputs. This preliminary action eliminates the harmful effect (out-of-band emissions) before it can be generated, while preserving the beneficial effect (transmitter efficiency improvement).
Solution Approach 2:
The invention changes the slew rate parameter of the envelope signal by redistributing maximum slew rate across input samples. This parameter modification smooths the supply voltage transitions, reducing spectral regrowth and out-of-band emissions while maintaining the efficiency benefits of envelope tracking.
2Power
If higher supply voltage is used to increase output power, then power output is improved, but power amplifier efficiency deteriorates
Solution Approach 1:
The supply voltage is made dynamic rather than static, varying in real-time to match the instantaneous envelope of the RF signal. This dynamic adjustment allows the PA to operate at higher voltages only when needed for peak power output, while maintaining lower voltages during low-power periods, thereby improving overall efficiency while preserving peak power capability.
Solution Approach 2:
The supply voltage parameter is continuously adjusted based on the envelope signal, changing from a fixed value to a time-varying parameter. This enables the PA to achieve high output power when required while maintaining high efficiency through voltage reduction during low-power intervals.
3Power
If DC-DC converter is used for average power tracking, then supply voltage control is achieved, but signal tracking speed is limited
Solution Approach 1:
The supply modulator is segmented into two distinct components: a DC-DC converter for efficient average power control and a linear amplifier for fast transient response. This segmentation allows each component to operate in its optimal regime, combining high efficiency with fast signal tracking capability.
Solution Approach 2:
The invention merges a DC-DC converter and a linear amplifier into a hybrid supply modulator. The DC-DC converter provides high efficiency for average power tracking, while the linear amplifier adds fast transient response capability, achieving both efficiency and speed that neither component could provide alone.
Data Source
AI summary
A communication unit includes a radio frequency, RF, transmitter having: a power amplifier, PA, module; and an envelope tracking system operably coupled to the PA module and having a supply modulator arranged to variably control a supply voltage for the PA module in response to a number of input samples of an envelope signal; wherein the envelope tracking system further includes at least one slew rate module arranged to re-distribute a maximum slew rate across the number of input samples in a provision of a variable power supply to the PA module.