Quadrature Power Amplifier Supply Modulation for RF Linearity
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Solution Overview
Problem
Digital modulated RF power amplifiers face challenges in achieving high power efficiency and linearity, particularly due to power back-off mode and large peak-to-average power ratio in multicarrier modulation methods like OFDM, leading to low average power levels and high adjacent channel interference in wideband applications such as LTE.
Innovation Solution
A quadrature power amplifier subsystem with DC to DC converters and variable gain amplifiers, where the supply path and gain path processes input signals to produce variable voltages and gain control signals, modulating the local oscillator signal to produce a modulated radio signal, and incorporating pre-distortion circuits to negate distortion, ensuring efficient power amplification with reduced bandwidth and phase mismatch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a quadrature modulated PA is used, then bandwidth expansion is reduced and implementation is easier, but power efficiency deteriorates compared to polar modulated PAs
Solution Approach 1:
The patent applies pre-distortion techniques to the I and Q channel signals before amplification. This preliminary action compensates for non-linearities in the power amplifier, enabling the quadrature modulated PA to achieve both ease of implementation and improved power efficiency by operating in a more efficient mode while maintaining signal integrity.
Solution Approach 2:
The patent dynamically adjusts the supply voltage to the power amplifier based on the instantaneous signal envelope. By changing the operating parameters of the amplifier in real-time, the system achieves higher power efficiency while maintaining the quadrature modulation architecture's implementation advantages.
2Use of energy by moving object
If a polar modulated PA is used, then power efficiency is improved, but bandwidth expansion increases causing adjacent channel interference
Solution Approach 1:
The patent applies pre-distortion filtering to the I and Q channel signals before modulation. This preliminary action removes spectral components that would cause bandwidth expansion and adjacent channel interference, allowing the system to achieve high power efficiency without the harmful side effects of polar modulation.
3Reliability
If power back-off mode is used to reduce peak-to-average power ratio, then linearity is improved, but average power efficiency deteriorates
Solution Approach 1:
The patent applies pre-distortion to the input signals before amplification. This preliminary compensation for non-linearities allows the power amplifier to operate at higher power levels without sacrificing linearity, thereby resolving the trade-off between linearity and power efficiency in power back-off mode.
Solution Approach 2:
The patent employs feedback mechanisms to monitor and adjust the amplifier's operating point. By continuously feedback the output signal and adjusting the pre-distortion parameters accordingly, the system maintains both linearity and power efficiency across varying operating conditions.
Data Source
Figure 1
Figure 2(a)~2(f)
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AI summary
A method and system for achieving increased efficiency in a quadrature modulated power amplifier (11) are disclosed. In some embodiments, a supply path (36, 40) and a gain path (38, 42) are provided in each of an I-channel and a Q-channel. The supply path (36, 40) produces a variable voltage and the gain path (38, 42) produces a gain control signal. The variable voltage and gain control signal are used by a variable gain power amplifier (44, 46) to modulate a local oscillator signal to produce a modulated radio signal.