Voltage Supply Stage for RF Amplifier Envelope Tracking
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Solution Overview
Problem
Existing envelope tracking power supplies for RF power amplifiers face challenges in achieving high bandwidth and low noise levels, particularly with conventional boost techniques resulting in low bandwidth and high wideband noise, and struggle to maintain average output voltage above the battery voltage, especially with low peak-to-average-power ratio signals.
Innovation Solution
A voltage supply stage incorporating a peak current mode switcher with a dual-output buck and boost switched mode topology, allowing for both buck and boost operations, and featuring a feedback path for full-spectrum frequency amplification, which includes a switched capacitor voltage doubler and a buck output stage capable of varying the average output voltage between 0 volts and twice the input supply voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional boost techniques are used in the voltage supply stage, then the output voltage can be higher than the input voltage, but the bandwidth becomes low and wideband noise levels increase
Solution Approach 1:
The voltage supply stage is divided into two separate paths: a high frequency path with a wideband linear amplifier and a low frequency path with an efficient switched mode amplifier. This segmentation allows each path to be optimized for its specific frequency range, enabling the system to achieve both high bandwidth (through the HF path) and voltage boosting capability (through the LF path)
Solution Approach 2:
The system dynamically switches between different amplification modes based on frequency content. The frequency splitter dynamically directs different frequency components to appropriate amplifiers, and the frequency selective combiner dynamically recombines them. This dynamic operation allows the system to maintain high bandwidth while achieving voltage boost when needed
2Power
If conventional boost techniques are used in the voltage supply stage, then the output voltage can be higher than the input voltage, but wideband noise levels become high
Solution Approach 1:
By segmenting the amplification function into separate HF and LF paths, the system isolates the noisy switched mode operation to only the low frequency path. The high frequency path uses clean linear amplification, so when HF components are present in the signal, they are amplified with low noise. The LF path handles only DC and very low frequency components where switched mode noise is less problematic
3Power
If a frequency selective combiner is used to combine HF and LF path signals, then the supply voltage can be generated, but tracking accuracy deteriorates
Solution Approach 1:
A feedback path is introduced that takes a portion of the combined output signal and feeds it back to the input of the linear amplifier. This feedback allows the system to continuously adjust and correct the HF path signal to maintain accurate tracking of the reference signal, compensating for any errors introduced by the frequency selective combining process
4Measurement precision
If an inductor-capacitor combiner is used, then the feedback path can be implemented for improved tracking, but ripple current losses increase
Solution Approach 1:
A capacitor is introduced as an intermediary element in the feedback path to block DC components while allowing AC signal components to pass. This intermediary allows the feedback mechanism to work effectively for tracking accuracy without forcing DC ripple currents through the inductor, thereby reducing ripple current losses while maintaining tracking performance
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 solution enhances the bandwidth and efficiency of the power supply, enabling it to maintain higher average output voltages above the battery voltage while minimizing ripple current losses and noise, thus addressing the limitations of conventional boost and buck-boost converters.
Implementation Method 1
A voltage supply stage is provided incorporating a peak current mode switcher. The voltage supply stage may further comprise a sixth switch (118) connected between the connection of the third (106) switch and the capacitor a further output, and a seventh (116) switch connected between the further output and the terminal of the input supply voltage
Data Source
Figure 1~2
Figure 3
Figure 4(a)~4(c)
AI summary
There is disclosed a voltage supply stage comprising an input supply voltage, a first (102) and second (104) switch connected in series, the first (102) and second (104) series-connected switches being connected in parallel with the input supply voltage between first and second terminals of the input supply voltage, a third (106) switch and capacitor connected in series, the series-connected third (106) switch and capacitor being connected in parallel with the first (102) switch, a fourth (108) switch connected between the connection of the third switch and the capacitor and an output, and a fifth (110) switch connected between the output and a terminal of the input supply voltage, wherein: in a first phase of operation, the first and the fourth switch are closed, and the second, third and fifth switches are open; in a second phase of operation, the second, third and fifth switches are closed, and the first and fourth switches are open; and the duty cycle of the first and second phases is controlled such that the average voltage on the output varies between 0 volts and twice the input supply voltage.