Wireless Transmitter EVM Detection for Amplifier Power Backoff Control
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Solution Overview
Problem
Existing wireless communication systems face challenges in efficiently transmitting signals at increased power without causing excessive interference to signals outside the desired frequency channel, often resulting in excessive power backoff that reduces transmission power.
Innovation Solution
The system includes a transmitter with an amplifier, a digital power meter, and an output power detector. The digital power meter estimates the crest factor of the input signal, while the output power detector measures the crest factor of the amplified signal. A controller adjusts the amplification factor based on the error vector magnitude, allowing for increased transmission power within the amplification headroom without entering the nonlinear region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the amplifier power is increased to improve transmission signal power, then the transmission signal quality improves, but interference to signals on other frequency channels increases
Solution Approach 1:
The system employs a feedback mechanism where the output signal from the amplifier is fed back through a feedback network that includes a directional coupler, power combiner, and detection circuitry. The detected signal characteristics are used to adjust the amplifier operation in real-time, enabling the system to maintain high transmission power while compensating for nonlinear distortion that causes interference to other channels.
Solution Approach 2:
A feedback network acts as an intermediary between the amplifier output and the control system. This network includes a directional coupler that samples the output signal, a power combiner that combines multiple signal components, and detection circuitry that measures signal characteristics. This intermediary structure enables precise monitoring and control of amplifier performance without directly interfering with the main signal path.
2Object-generated harmful factors
If power backoff is applied to reduce interference to other channels, then interference is reduced, but transmission signal power decreases
Solution Approach 1:
The feedback mechanism continuously monitors the amplifier output and provides real-time adjustment signals. This allows the system to operate the amplifier at higher power levels without excessive backoff, maintaining transmission signal power while using the feedback control to minimize interference to other channels through dynamic compensation of nonlinear effects.
Solution Approach 2:
The system dynamically changes operational parameters including amplifier bias conditions and feedback control signals based on real-time signal characteristics. By adjusting these parameters, the system can optimize the trade-off between transmission power and interference levels, avoiding the need for excessive power backoff while maintaining acceptable interference levels.
Data Source
AI summary
An amplifier of a transmitter includes an input that receives an input signal and generates an amplified signal at an output. A digital power meter is coupled to the input of the amplifier, generates an estimated amplified signal, and determines peak and average powers of the estimated amplified signal. An output power detector coupled to the output of the amplifier determines peak and average powers of the amplified signal. A controller coupled to the digital power meter and the output power detector determines an estimated crest factor based on the peak and average powers of the estimated amplified signal, an amplified crest factor based on the peak and average powers of the amplified signal, and an error vector magnitude based on the estimated and amplified crest factors. The controller, which is also coupled to the amplifier, then adjusts operation of the amplifier based on the error vector magnitude.