Dynamic Transmitter Calibration for RF Power Amplifiers
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Solution Overview
Problem
Radio frequency (RF) transmitters generate out-of-band energy due to non-linear power amplifiers, leading to interference with adjacent channels and limiting performance, as they typically operate below maximum output power to avoid distortion, requiring costly calibration and not accounting for temperature variations.
Innovation Solution
A method and apparatus that generate an indicator of interference, specifically a carrier-to-interference (C/I) ratio, to dynamically adjust the power level of the output transmit signal, using a filter module and gain control module to maintain the C/I ratio above a predetermined level, thereby optimizing power amplification while minimizing out-of-band energy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the transmitter operates at maximum output power to improve productivity, then the power amplifier introduces excessive out-of-band energy and distortion, but operating below maximum power reduces interference with adjacent channels
Solution Approach 1:
The system dynamically adjusts the power amplifier's operating point by applying back-off based on real-time temperature measurements and distortion indicators. The power level is not fixed but varies adaptively to maintain optimal performance across changing thermal conditions, resolving the contradiction between maximum power output and distortion control
Solution Approach 2:
The system employs feedback mechanisms where distortion indicators and temperature sensors provide real-time information about the power amplifier's performance. This feedback loop enables automatic adjustment of the operating point to maintain compliance with spectral masks while maximizing output power, addressing the trade-off between productivity and harmful emissions
2Manufacturing precision
If individual transmitter calibration is performed to improve manufacturing precision, then distortion levels are optimized, but calibration time and non-volatile memory requirements increase device complexity
Solution Approach 1:
The system performs self-calibration by automatically determining its own distortion characteristics through temperature-dependent distortion indicators. Rather than requiring external calibration equipment and procedures, the transmitter self-adjusts its operating parameters based on real-time measurements, eliminating the need for complex calibration infrastructure while maintaining precision
Solution Approach 2:
The system changes operating parameters dynamically based on temperature conditions. By adjusting the power back-off level according to measured temperature and distortion indicators, the system adapts to varying thermal conditions without requiring separate calibration data for each temperature scenario, reducing memory requirements while maintaining precision
3Reliability
If the transmitter operates with substantial margin below distortion limits to improve reliability, then interference is reduced, but the usable power level and productivity decrease
Solution Approach 1:
The system dynamically determines the appropriate back-off level rather than using a fixed conservative margin. By continuously monitoring temperature and distortion indicators, the system adjusts the power level to operate as close as possible to the distortion limits while maintaining compliance, thereby maximizing productivity without sacrificing reliability
Solution Approach 2:
The operating parameters are changed adaptively based on real-time conditions. The power back-off level is not static but varies with temperature and measured distortion characteristics, allowing the system to maintain reliability while extracting maximum usable power from the amplifier under different operating conditions
Data Source
AI summary
A method includes generating an indicator of interference introduced by a transmitter into a spectrum of an output transmit signal outside a target channel of the transmitter. The indicator is generated based on the output transmit signal. The method includes adjusting a power level of the output transmit signal based on the indicator and a predetermined interference indicator level. The indicator may indicate a carrier-to-interference (C/I) ratio of the output transmit signal, and the adjusting comprises setting the power level of the output transmit signal to a maximum power level that maintains the C/I ratio of the output transmit signal above the predetermined interference indicator level. The output transmit signal may be based on a radio-frequency output of a power amplifier of the transmitter prior to transmission over a channel and the generating comprises generating a baseband version of the output transmit signal.