WCDMA Transmitter Power Control Using AM-Removed Gain Feedback
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Solution Overview
Problem
Traditional power control systems for mobile terminals operating under WCDMA are not suitable for fast and accurate gain adjustments within the first 50 microseconds of a time slot, as they require approximately 200 microseconds to remove amplitude modulation, which is not feasible for continuous transmission schemes like WCDMA.
Innovation Solution
A power control circuitry that processes a quadrature baseband signal to provide a feedback amplitude signal, using a reference amplitude signal to remove amplitude modulation components and determine the gain, allowing for rapid adjustment of the transmitter gain within the first 50 microseconds of each time slot, using delay circuitry and logarithmic conversion to ensure accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional power control systems use a closed loop architecture with an averaging filter to measure gain, then measurement accuracy is improved, but the response time increases to approximately 200 microseconds, which is too slow for WCDMA requirements
Solution Approach 1:
The patent extracts the amplitude modulation component from the feedback signal using a reference amplitude signal generated from the quadrature baseband signal. By removing the amplitude modulation through division rather than filtering, the system achieves fast gain measurement without requiring a slow averaging filter, thus resolving the contradiction between measurement accuracy and response speed
Solution Approach 2:
The patent replaces the mechanical filtering approach (averaging filter) with a signal processing approach (division of feedback signal by reference amplitude signal). This substitution eliminates the need for a slow averaging filter while maintaining gain measurement accuracy, enabling response times within the 50 microsecond WCDMA requirement
2Stability of the object's composition
If power control systems detect gain in one time slot and adjust gain in the next time slot, then system stability is improved, but accuracy deteriorates because the bias current may change between time slots
Solution Approach 1:
The patent generates the reference amplitude signal in advance from the quadrature baseband signal before the power amplification stage. This preliminary generation of the reference signal ensures that when the feedback signal is processed, the bias current conditions are identical, eliminating errors caused by bias current changes between measurement and adjustment time slots
3Use of energy by moving object
If the bias current of the transmitter is decreased to reduce current consumption and extend battery life, then energy efficiency is improved, but the gain and power step of the transmitter change, requiring additional power control adjustments
Solution Approach 1:
The patent implements a feedback mechanism where the measured gain signal (obtained by dividing the feedback amplitude signal by the reference amplitude signal) is used to control the gain of the transmit circuitry. This closed-loop feedback automatically compensates for gain changes caused by bias current adjustments, enabling energy efficiency improvements without excessive system complexity
Solution Approach 2:
The power control system uses itself to compensate for its own changes. When bias current changes affect transmitter gain, the system automatically measures the new gain condition and adjusts accordingly, making the power control system self-correcting and reducing the need for external intervention or complex control mechanisms
Data Source
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AI summary
Power control circuitry is provided for controlling an output power of a transmitter of a mobile terminal operating according to a continuous time transmit scheme such as Wideband Code Division Multiple Access (WCDMA). Transmit circuitry processes a quadrature baseband signal to provide a radio frequency transmit signal. The radio frequency transmit signal is coupled to the power control circuitry via a coupler and processed to provide a feedback amplitude signal. The power control circuitry operates to remove an amplitude modulation component from the feedback signal using a reference amplitude signal generated from the quadrature baseband signal, thereby providing a measured gain signal of the transmit circuitry. Based on the measured gain signal and a target output power, the power control circuitry operates to control a gain of the transmit circuitry such that the output power of the transmit circuitry is within a predetermined range about the target output power.