Power Amplifier Envelope Tracking with Peak-Stretch Filtering
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Solution Overview
Problem
Optimizing the efficiency of an envelope tracking power amplifier is challenging due to the need for a controllable voltage source with high bandwidth to manage variations in supply voltage, leading to increased power losses and complex calibration processes, especially when dealing with high peak-to-average ratio output signals.
Innovation Solution
A non-linear filter is used to preserve the rise time of envelope signal peaks while lengthening their temporal duration, allowing for a lower control bandwidth and reduced power losses by making it easier for the control system to react to peaks, thereby improving amplifier efficiency and reducing calibration complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the bandwidth of the controllable voltage source is increased to closely follow envelope variations, then clipping is avoided and amplifier efficiency is improved, but power losses in the voltage source increase due to higher switching frequency
Solution Approach 1:
The patent applies preliminary action by detecting envelope peaks in advance and maintaining a higher supply voltage level before the peaks occur. The envelope detector identifies upcoming peaks, and the supply voltage is proactively adjusted to a higher level to ensure sufficient headroom for the anticipated signal peaks, preventing clipping before it occurs. This approach allows the supply voltage to be reduced afterward, minimizing average power consumption while maintaining reliability.
2Speed
If the switching frequency of the SMPS is increased to achieve higher bandwidth, then the supply voltage can follow envelope variations more closely, but switching losses increase
Solution Approach 1:
The system performs preliminary detection of envelope peaks and proactively adjusts the supply voltage before the peaks occur. By anticipating the need for higher voltage levels, the control system can use lower switching frequencies while still achieving the required bandwidth performance, as the voltage adjustments are made in advance rather than requiring high-speed real-time tracking.
Solution Approach 2:
The patent implements dynamic adjustment of the supply voltage based on detected envelope characteristics. The system transitions from static high voltage operation to dynamic voltage scaling, where the supply voltage is adjusted in real-time according to the actual signal envelope requirements. This dynamic approach allows the system to operate at lower switching frequencies while maintaining the necessary voltage tracking performance.
3Reliability
If the supply voltage is kept high to provide safety margin for envelope variations, then clipping is prevented, but unnecessary power losses occur in the output stage transistors
Solution Approach 1:
The envelope detector identifies upcoming signal peaks in advance, allowing the supply voltage to be proactively increased to appropriate levels before the peaks occur. This preliminary detection and response mechanism ensures sufficient voltage headroom is available when needed while allowing the voltage to be reduced to lower levels during periods when high power is not required, minimizing average power losses in the output stage transistors.
4Reliability
If a high control bandwidth is used to track sharp envelope peaks, then clipping is avoided, but the calibration process becomes more complex and slower
Solution Approach 1:
The system performs preliminary detection and identification of envelope peaks, using this information to proactively adjust the supply voltage. By detecting peaks in advance and responding proactively, the system achieves accurate peak tracking with simpler calibration requirements, as the envelope detection provides natural timing references that simplify the alignment process between the supply voltage adjustments and the signal peaks.
Data Source
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Figure 5a~5f
AI summary
The invention relates to optimizing efficiency of a power amplifier of a transmitter. In a solution according to the invention a detected envelope (306) of an input signal of the power amplifier is filtered with a non-linear filter (307) that substantially preserves a rise time of a peak in a waveform of the envelope but lengthens a temporal duration of the peak. A filtered envelope is used as an input quantity (308) for a control system that controls a supply voltage of the power amplifier. For the control system it is easier to react to peaks of the filtered envelope than to the peaks of the envelope because the temporal duration of the peaks of the filtered envelope is longer than that of the peaks of the envelope.