Quadrature Power Amplifier Modulation for Efficiency
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Cellular devices using quadrature modulation schemes face inefficiencies in power amplifiers due to linearity issues, leading to reduced battery life and harmonic interference, especially when transmitting large bandwidth signals.
Innovation Solution
A communications device with separate In-phase (I) and Quadrature (Q) power amplifiers operating in saturated mode, using digital-to-analog converters and power supply circuits to generate constant envelope signals, and employing phase locked loops and look-up tables for linear signal modulation, with antennas configured for efficient signal combination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If quadrature modulation schemes are used to transmit large bandwidth signals, then signal transmission capability is improved, but power amplifier efficiency deteriorates due to linearity issues
Solution Approach 1:
The patent divides the quadrature modulation signal into separate in-phase (I) and quadrature (Q) components, each processed by independent power amplifiers. This segmentation allows each amplifier to operate efficiently on constant-envelope signals while maintaining the overall signal integrity through proper recombination of the I and Q paths.
2Reliability
If peak power is increased to maintain signal quality in quadrature modulation, then transmission reliability is improved, but average power consumption increases reducing battery life
Solution Approach 1:
The patent changes the amplitude parameter of the modulation signal to maintain a constant envelope while preserving phase information. By converting variable-amplitude quadrature signals into constant-amplitude form with phase encoding, the power amplifier can operate at peak efficiency without requiring peak power backoff, thus maintaining signal quality while reducing average power consumption.
3Manufacturing precision
If power amplifier operates in backed-off condition to maintain linearity, then signal distortion is reduced, but power efficiency deteriorates
Solution Approach 1:
Instead of backing off the power amplifier to maintain linearity, the patent inverts the approach by making the signal constant-envelope and allowing the amplifier to operate in saturated nonlinear mode. The linearity is then restored through the specific modulation technique that encodes information in phase rather than amplitude, eliminating the need for linear operation.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A communications device (20) may include an In-phase (I) power amplifier (22) configured to generate an I amplified signal, a Quadrature (Q) power amplifier (21) configured to generate a Q amplified signal, an I digital-to-analog converter (DAC) (26) configured to generate an I signal, and a Q DAC (25) configured to generate a Q signal. The communications device may also include an I power supply circuit (24) coupled to the I power amplifier and to the I DAC and configured to cause the I power amplifier to modulate an I carrier signal into the I amplified signal based upon the I signal, a Q power supply circuit (23) coupled to the Q power amplifier and to the Q DAC and configured to cause the Q power amplifier to modulate a Q carrier signal into the Q amplified signal based upon the Q signal, and at least one antenna (27-28) coupled to the I and Q power amplifiers.