RF Transmitter Pre-Distortion for Memory-Effect Linearity
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Solution Overview
Problem
Current digital pre-distortion techniques for radio frequency transmitters are complex and not suitable for small devices, and require high precision to minimize time of arrival misalignments to achieve high signal fidelity and linearity, while existing memoryless techniques cannot compensate for memory effects.
Innovation Solution
A method using different pre-distortion parameters for increasing and decreasing input amplitudes, determined by a baseband processing unit, to improve digital pre-distortion performance and reduce complexity, allowing for high signal fidelity and linearity in radio frequency devices, including mobile devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If memory mitigation digital pre-distortion is used to compensate memory effects, then signal fidelity is improved, but device complexity increases making it unsuitable for small radio frequency devices
Solution Approach 1:
The patent segments the pre-distortion process into two distinct phases: an upward ramp phase for increasing input amplitudes and a downward ramp phase for decreasing input amplitudes. By dividing the measurement and calibration process into these separate segments, the system achieves accurate compensation of memory effects without requiring the complex continuous measurement systems of traditional memory mitigation techniques. Each ramp phase uses specific pre-distortion parameters optimized for that direction of amplitude change.
Solution Approach 2:
The patent implements periodic up-and-down amplitude ramps as a cyclic measurement procedure. The transmitter unit undergoes repeated cycles of increasing and decreasing input amplitudes, allowing the system to periodically update pre-distortion parameters for both upward and downward ramps. This periodic action enables continuous adaptation to memory effects while maintaining a simple, repeatable measurement sequence suitable for integration in small devices.
2Use of energy by moving object
If envelope tracking technique is used to minimize power consumption, then power consumption is reduced, but signal linearity degrades due to time of arrival misalignments between envelope signal and RF signal
Solution Approach 1:
The patent applies preliminary digital pre-distortion to the RF signal before transmission, which compensates for the time of arrival misalignments caused by envelope tracking. By pre-distorting the signal with inverted distortion characteristics in the baseband domain, the system proactively corrects the linearity degradation that would otherwise occur when the envelope signal and RF signal arrive at different times at the power amplifier.
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AI summary
A method for measuring characteristics of a transmitter unit (42) of a device under test (14) is described. A signal generator (12) is provided that comprises a baseband processing unit (18) having at least a digital pre-distortion sub-unit (20). A device under test (14) is provided that has a transmitter unit (42). A measuring unit (50) is provided. Said signal generator (12) and said device under test (14) are connected with each other via an interface (16). At least one input signal is generated by using said signal generator (12), said input signal is forwarded to said device under test (14). An output signal of said device under test (14) is measured by using said measuring unit (50). A first pre-distortion parameter for an increasing input amplitude is determined by using said digital pre-distortion sub-unit (20). A second pre-distortion parameter for a decreasing input amplitude is determined by using said digital pre-distortion sub-unit (20). Said first and second pre-distortion parameters are determined such that said output signal has a high fidelity. Further, a test system (10) and a radio frequency device (54) are described.