Switched-Capacitor Power Amplifier Half-Amplitude Back-Off Control
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Solution Overview
Problem
Switched-capacitor power amplifiers experience efficiency degradation at back-off conditions due to the need for disabling cells, which attenuate the output signal and consume power, especially for signals with high peak-to-average power ratios, and existing solutions either have limited amplitude range, increased overhead, or require complex circuitry.
Innovation Solution
Implementing a switching scheme that includes a 'half amplitude' mode in addition to 'full amplitude' and 'off' modes in each cell, allowing for efficient operation at reduced output amplitudes without losing peak output power and using only one power supply voltage, thereby maintaining efficiency across various back-off levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If cells are disabled to reduce output amplitude, then output power is reduced, but efficiency degrades rapidly
Solution Approach 1:
The patent segments the output amplitude control into three distinct modes (full amplitude, half amplitude, and off) for each cell. Instead of completely disabling cells for amplitude reduction, the invention divides the amplitude range into discrete segments, allowing cells to operate in a half-amplitude state that maintains efficiency while reducing output power. This segmentation resolves the contradiction by providing intermediate operating states between full power and complete shutdown.
Solution Approach 2:
The patent implements dynamic switching between full amplitude, half amplitude, and off states based on the desired output level. The control logic dynamically selects the appropriate combination of cell states to achieve the target amplitude while maximizing efficiency. This dynamic operation allows the amplifier to adapt to varying output requirements without suffering from the efficiency degradation associated with static cell disabling.
2Loss of energy
If supply voltage is used to modulate output amplitude, then efficiency at back-off improves, but amplitude range is limited and transfer is highly non-linear
Solution Approach 1:
The patent segments the amplitude control into discrete half-amplitude steps rather than continuous modulation. Each cell can independently operate in full amplitude, half amplitude, or off states, creating a segmented amplitude control scheme. This approach achieves efficient back-off operation through discrete amplitude levels while maintaining a linear relationship between control signals and output amplitude, avoiding the non-linearity issues of supply voltage modulation.
Solution Approach 2:
The patent changes the operating parameter from supply voltage modulation to cell state switching. Instead of varying the supply voltage to control amplitude (which causes non-linearity), the invention changes the operational state of individual cells between full amplitude, half amplitude, and off modes. This parameter change enables efficient back-off operation while maintaining amplitude linearity and extending the usable amplitude range.
3Loss of energy
If two power supplies are used to improve efficiency at back-off, then efficiency improves, but overhead due to additional power supply and connections increases
Solution Approach 1:
The patent makes the single power supply serve multiple functions by enabling cells to operate in full amplitude, half amplitude, and off states using the same supply voltage. The half-amplitude mode achieves back-off efficiency without requiring a second power supply, as it uses the existing supply voltage in a different operational configuration. This multi-functionality resolves the contradiction by eliminating the need for additional power supply infrastructure while maintaining efficiency benefits.
4Loss of energy
If Doherty amplifier configuration is used, then efficiency at back-off improves, but frequency range is limited and design effort increases
Solution Approach 1:
The patent applies segmentation by dividing the amplifier into independent cells that can be individually controlled in full amplitude, half amplitude, or off states. This segmented architecture achieves efficient back-off operation without requiring the complex frequency-matched networks of a Doherty amplifier. The independent cell control provides flexibility across frequency ranges while maintaining simplicity in the overall design approach.
Data Source
Figure 1~2
Figure 3a~3b
Figure 4a~4b
AI summary
A switched-capacitor power amplifier comprising a plurality of cells is described. Switched signal lines switch supply to respective capacitors (110, 120). Switches (130, 150) connect respective signal lines to a first supply (Vdd) and switches (140, 160) connect respective signal lines to a second supply (Vss). Pairs of switches on each signal line are switched so that one is switched off whilst the other is switched on. In a "full amplitude" mode, operation of the switches provides an output having a peak determined by the first supply. A switch signal line is provided between nodes (220, 230) in respective signal lines, a switch (210) being provided in the switch signal line. In a "half amplitude" mode, switch (210) is switched at the radio frequency in the other direction to that of switches (130, 160) connecting the signal lines to respective ones of the first and second supplies with the other switches (140, 150) being kept open.