Polar Loop RF Transmitter Dynamic Range Control for AM-PM Signals
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Solution Overview
Problem
Existing GSM transmitter hardware is inefficient in handling signals with both phase and amplitude modulation due to the need for highly linear power amplifiers, which consume more power and reduce battery life, and struggles to maintain dynamic range control for output power levels, leading to undesirable AM to PM conversion.
Innovation Solution
A closed-loop power control system with variable gain elements and a comparator to manage power levels, allowing for efficient control of both phase and amplitude modulation signals using a non-linear power amplifier, and a 'soft step' gain function to maintain dynamic range control during power ramp-up and ramp-down.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a highly linear power amplifier is used to transmit combined AM and PM signals, then signal quality is improved, but power consumption increases and battery life is reduced
Solution Approach 1:
The patent segments the power amplifier into two distinct paths: a linear power amplifier dedicated to AM signals and a non-linear power amplifier dedicated to PM signals. This segmentation allows each amplifier to operate in its optimal efficiency region while maintaining overall signal quality, thereby reducing total power consumption compared to using a single highly linear amplifier for both signal types.
Solution Approach 2:
The patent changes the operational parameters of the power amplifiers by allowing the non-linear amplifier to handle PM signals without requiring high linearity, while the linear amplifier handles only AM signals. This parameter change enables the non-linear amplifier to operate at higher efficiency points, reducing overall power consumption while maintaining signal integrity through the dual-path architecture.
2Use of energy by moving object
If a non-linear power amplifier is used for efficient transmission, then power consumption is reduced, but the ability to handle combined AM and PM signals is lost
Solution Approach 1:
The patent segments the signal handling function into two separate amplification paths: one path with a linear power amplifier dedicated to AM signals and another path with a non-linear power amplifier dedicated to PM signals. This segmentation enables the system to use efficient non-linear amplification for PM signals while maintaining the ability to handle AM signals through the linear path, thus achieving both efficiency and versatility.
Solution Approach 2:
The patent creates a multi-functional power amplification system where two different types of power amplifiers work in parallel to handle different modulation types. The linear power amplifier handles AM signals while the non-linear power amplifier handles PM signals, giving the system the universal capability to efficiently transmit both AM and PM modulated signals simultaneously.
3Reliability
If a power control loop is used to maintain constant output power, then power stability is improved, but amplitude variations in AM signals are attenuated
Solution Approach 1:
The patent extracts the amplitude control function from the feedback power control loop by placing the AM signal input directly at the input of the linear power amplifier, bypassing the feedback loop. The feedback loop then only controls the overall power level through the non-linear amplifier's PM path, allowing the AM amplitude variations to pass through unaffected while still maintaining stable overall output power.
Solution Approach 2:
The patent segments the control functions by having the feedback power control loop manage only the PM path through the non-linear amplifier, while the AM path through the linear amplifier operates independently with its amplitude control. This segmentation prevents the feedback loop from attenuating AM amplitude variations while still maintaining overall power stability.
4Adaptability or versatility
If the dynamic range of the power control loop is increased, then output power control range is improved, but complexity of the control system increases
Solution Approach 1:
The patent extracts the AM signal path from the feedback control loop, placing it directly at the input of the linear power amplifier. This extraction allows the feedback loop to focus solely on controlling the non-linear amplifier's PM path, simplifying the control system architecture while still achieving wide dynamic range power control through the combined operation of both amplifiers.
Solution Approach 2:
The patent inverts the traditional approach by having the feedback loop control the non-linear amplifier rather than the linear amplifier. This inversion simplifies the control system because the non-linear amplifier's output can be more easily controlled over a wide dynamic range through feedback, while the linear amplifier handles the AM signal independently, reducing overall system complexity.
Data Source
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AI summary
A closed loop power control system for a radio frequency (RF) transmitter comprises a first variable gain element located in a power control loop and configured to receive a power level signal and an inverse representation of a power control signal, a second variable gain element located in the power control loop and configured to receive an error signal and the power control signal, and a third variable gain element configured to receive an amplitude modulated (AM) signal and the power control signal, the third variable gain element having a gain characteristic configured to operate to reduce the gain applied to the AM signal when the power control signal falls below a minimum predetermined value, and to provide the AM signal as a reference signal.