Amplifier Output Power Control with RST Regulation for Fast CDMA Response
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Solution Overview
Problem
In CDMA systems, particularly W-CDMA, the power amplifier in remote terminals like cellular mobile phones faces challenges in quickly adjusting transmission power due to significant ripple in the output signal with varying envelope modulation, which requires long filtering times incompatible with the need for rapid power adjustments.
Innovation Solution
A method using a polynomial digital regulator of the RST type to control the output power of an amplifier circuit, decoupling the filtering time from the time required for establishing new transmission power by generating filtered digital information and applying gain and bias current controls based on input parameters and characteristics of the amplifiers and filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If filtering is applied to remove ripple from the output signal, then measurement precision is improved, but response time deteriorates due to long filtering time constant
Solution Approach 1:
The filtering operation is segmented into two independent parts: a first filter with a first time constant processes the detector output signal, and a second filter with a second time constant processes the digital information representing output power. This segmentation allows each filter to be optimized for its specific function, resolving the contradiction between ripple removal and fast response.
Solution Approach 2:
Digital information serves as an intermediary between the analog detector output and the power adjustment control. The digital information is generated by converting the analog signal and applying digital filtering, which provides precise power measurement without the time constant limitations of analog filtering, thereby enabling fast response while maintaining measurement accuracy.
2Reliability
If a long time constant filter is used to filter the output signal, then reliability of power measurement is improved, but productivity deteriorates due to slow power establishment
Solution Approach 1:
The system dynamically adapts the filtering characteristics to the specific modulation signal being processed. The first filter time constant is specifically chosen to match the ripple characteristics of the modulated signal, while the second filter provides additional smoothing for digital processing. This dynamic adaptation ensures reliable power measurement without unnecessarily slowing down the power adjustment response.
Solution Approach 2:
The filtering parameters (time constants) are changed and optimized for different operating conditions and modulation types. By adjusting the filter time constants according to the specific signal characteristics, the system achieves both reliable power measurement and fast response, resolving the contradiction between measurement reliability and adjustment speed.
Data Source
AI summary
Filtered digital information representative of the power of an output signal from an amplifier is generated, and control information from a setpoint representative of a desired power for the output signal is generated from the desired response time for the establishment of the power and from a model to be followed for the establishment. In addition, a gain control and a bias current control are established for each initial variable-gain amplifier from the filtered digital information, from the control information and from a polynomial digital regulation of the RST type whose polynomial coefficients are determined from input parameters comprising characteristics of each variable-gain amplifier and from characteristics of the filter generating the filtered digital information.