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 maintain optimal supply voltage, which results in high 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 easier control of the supply voltage and reducing the required control bandwidth, thereby minimizing power losses and simplifying calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the supply voltage is kept high to avoid clipping, then no clipping occurs in the output signal, but power losses increase unnecessarily
Solution Approach 1:
The supply voltage is dynamically adjusted to follow the envelope of the input signal rather than being kept constantly high. The controllable voltage source modifies the supply voltage in real-time based on the detected envelope, allowing the voltage to be high only when necessary to prevent clipping and low otherwise to minimize power losses.
Solution Approach 2:
The supply voltage parameter is changed dynamically according to the envelope signal characteristics. By varying the voltage level based on the instantaneous envelope value, the system maintains reliability when needed while reducing energy losses during periods when high voltage is not required.
2Speed
If the switching frequency is increased to achieve high bandwidth, then the controllable voltage source responds faster to envelope variations, but switching losses increase
Solution Approach 1:
Instead of providing excessive bandwidth through high switching frequency, the system applies partial action by using a moderate switching frequency combined with envelope detection. The envelope detector extracts only the necessary amplitude information, allowing the voltage source to respond adequately without requiring excessive bandwidth and high switching frequencies that would cause high losses.
3Reliability
If the control bandwidth is increased to track envelope variations accurately, then clipping is avoided, but calibration complexity and power losses increase
Solution Approach 1:
The invention extracts the essential envelope information from the high-frequency signal using an envelope detector. By separating the envelope detection function from the voltage control, the system achieves accurate tracking without requiring the entire control system to operate at high bandwidth, thereby reducing calibration complexity while maintaining reliability.
Data Source
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.