RF Transmit Circuit Using PWM Amplitude Modulation for Efficient Power Control
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Solution Overview
Problem
Current power amplifiers for cellular telephone terminals and wireless LANs face inefficiencies due to amplitude modulation, leading to distortion and increased power consumption, especially when trying to integrate signal generator circuits into a single semiconductor die using CMOS technology, which struggles with high transistor saturation voltage and limited power control range.
Innovation Solution
An RF transmit circuit is developed, incorporating a signal processing circuit and a nonlinear amplifier that generates a pulse width modulated signal to produce an amplitude-modulated output, allowing for efficient amplitude and phase control without complex biasing schemes, using a transformer to convert differential signals into single-ended signals for efficient power amplification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If linear amplifiers with head room are used to amplify amplitude-varying signals, then signal quality is improved, but power efficiency deteriorates
Solution Approach 1:
The patent implements dynamic control of the power amplifier by varying the supply voltage to the PA according to the envelope of the amplitude-modulated signal. This dynamic voltage adjustment allows the PA to operate efficiently across different signal power levels while maintaining signal quality, resolving the contradiction between linear operation and power efficiency.
Solution Approach 2:
The invention changes the operating parameters of the power amplifier by adjusting the supply voltage in real-time based on signal requirements. This parameter modulation enables the PA to adapt its efficiency characteristics to match the instantaneous power demands of amplitude-varying signals, achieving both good signal quality and improved power efficiency.
2Use of energy by moving object
If control circuitry complexity is increased to maintain optimal efficiency for all amplification requirements, then power efficiency is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent extracts the complexity from the control circuitry by using a simple envelope detector to capture the signal amplitude variations, and then uses this extracted envelope information to directly modulate the PA supply voltage. This approach maintains power efficiency without requiring complex control systems, resolving the contradiction between efficiency and complexity.
Solution Approach 2:
The system achieves efficient operation through self-regulation by using the signal's own envelope to control the PA supply voltage. The envelope detector automatically extracts the amplitude information, and this information directly controls the voltage adjustment, creating a self-adapting system that maintains efficiency without external complex control.
3Adaptability or versatility
If parallel PAs are used with phase control for amplitude modulation, then adaptability is improved, but power efficiency deteriorates due to output power waste
Solution Approach 1:
The patent merges the amplitude modulation function and power control function into a single supply voltage modulation mechanism. Instead of using separate parallel PAs with phase control, the invention combines these functions by modulating the supply voltage of a single PA according to the signal envelope, achieving amplitude modulation while maintaining high power efficiency.
Data Source
AI summary
Disclosed is a method and apparatus for amplitude modulation of an RF transmit signal using pulse width modulation to control an amount of energy within each period. The apparatus includes a signal processing circuit with an input port for receiving of information indicative of a carrier frequency and modulation data. The signal processing circuit has a first output port and a second output port for providing of output signals having a phase relationship therebetween. A power amplifier is provided for receiving the output signals and for generating a pulse width modulated signal in dependence thereon.