Power Amplifier Bias Calibration for IMD3 and ACPR Control
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Solution Overview
Problem
Wireless distribution systems (WDS) face challenges in reducing radio frequency (RF) interference, particularly in uplink RF communications signals, due to the non-linearity of high-power power amplifiers used in remote units of distributed antenna systems (DAS), which leads to intermodulation products and adjacent channel interference, affecting RF coverage and performance.
Innovation Solution
A power amplifier calibration circuit is employed to optimize third-order intermodulation (IMD3) and adjacent channel power ratio (ACPR) by adjusting first and second bias signals, using a control circuit to rank performance parameters and determine optimal bias signal combinations, thereby calibrating the power amplifier for improved linearity and reduced interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high-power power amplifiers are used to amplify downlink communications signals, then the coverage range and signal strength are improved, but intermodulation products and adjacent channel interference are generated due to non-linearity
Solution Approach 1:
The patent applies parameter changes by adjusting the bias signals (first and second bias signals) of the power amplifier to optimize its operating point. This allows the amplifier to operate in a region that balances output power with linearity, reducing intermodulation products and adjacent channel interference while maintaining adequate coverage range.
Solution Approach 2:
The patent implements feedback through a calibration process where the power amplifier's performance parameters (IMD3 and ACPR) are measured and used to adjust the bias signals. This closed-loop approach enables the system to automatically optimize the amplifier's operating conditions to minimize harmful interference while maintaining desired output power levels.
2Manufacturing precision
If multiple bias signal combinations are tested to optimize performance parameters, then the linearity and interference reduction are improved, but the calibration time and complexity increase
Solution Approach 1:
The patent applies preliminary action by pre-defining a set of candidate bias signal combinations that are likely to yield optimal performance. Instead of exhaustively searching all possible combinations, the system prepares a curated list of promising candidates in advance, reducing the calibration time while still achieving good optimization results.
Solution Approach 2:
The patent uses partial action by testing a limited subset of bias signal combinations rather than all possible combinations. The control circuit ranks the measured performance parameters from this subset and selects the best combination, achieving sufficient optimization without the time cost of exhaustive search.
Data Source
AI summary
Embodiments of the disclosure relate to calibrating a power amplifier. The power amplifier calibration circuit is configured to provide a plurality of bias signal combinations each including a respective first bias signal and a respective second bias signal to the power amplifier. Power amplifier performance parameters for each of the bias signal combinations can be measured and provided to a control circuit in the power amplifier calibration circuit. The control circuit is configured to rank the measured power amplifier performance parameters based on predefined ranking criteria and determines a selected bias signal combination that can optimize the power amplifier performance parameters of the power amplifier. As such, it is possible to calibrate the power amplifier to operate at a balanced performance level, thus helping to improve radio frequency (RF) coverage and performance of the remote unit in a wireless distribution system (WDS).