SC-DAC Digital RF Transmitter for Harmonic Cancellation
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Solution Overview
Problem
Recent wireless communication systems, especially those supporting multiple bands and modes like 5G, face challenges with intermodulation distortion due to non-linear amplification, which increases the number and cost of filters required to mitigate this distortion, particularly in millimeter-wave bands.
Innovation Solution
A digital RF transmitter is designed with a switched-capacitor digital-to-analog converter (SC-DAC) that generates pattern signals with specific phase differences to remove harmonic components, thereby reducing intermodulation distortion by amplifying these signals to a certain magnitude ratio and synthesizing them into the RF analog signal, using processing circuitry to generate I-Q and inverted I-Q binary data pairs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a non-linear amplifier is used to generate RF analog signal, then amplification efficiency is improved, but intermodulation distortion components are generated
Solution Approach 1:
The patent applies preliminary action by generating compensation signals in advance that contain the intermodulation distortion components, then combining these compensation signals with the original RF signal before amplification. This pre-compensation approach allows the non-linear amplifier to operate efficiently while the distortion components are already present in the signal to be amplified, enabling subsequent cancellation without requiring the amplifier to be linear.
Solution Approach 2:
The patent converts the harmful intermodulation distortion into a beneficial element by intentionally generating compensation signals that contain the same distortion components. These distortion components, when combined with the original signal and properly phased, cancel out the actual intermodulation distortion produced by the non-linear amplifier, transforming the harmful effect into a solution.
2Reliability
If filters are added to remove intermodulation distortion components, then signal purity is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces the mechanical/filter-based approach to distortion removal with a signal processing approach. Instead of using physical filters to remove intermodulation distortion components after amplification, the system uses digital signal generation and combination to pre-compensate for distortion, eliminating the need for complex filter networks and reducing device complexity.
3Reliability
If filters are added to remove intermodulation distortion components, then signal purity is improved, but layout area and cost increase
Solution Approach 1:
The patent replaces the physical filter structures with a signal processing solution that requires minimal additional circuit area. The compensation signal generation uses digital logic and signal combination circuits that occupy significantly less layout area compared to the filter networks that would be required to achieve the same distortion removal performance.
Data Source
AI summary
A digital radio frequency (RF) transmitter including processing circuitry configured to generate first through third pattern signals based on a pattern of an inphase (I)-quadrature (Q) binary data pair and a pattern of an inverted I-Q binary data pair, the first through third pattern signals having a same pattern and different phases, and a switched-capacitor digital-to-analog converter (SC-DAC) configured to remove an n-th harmonic component of an RF analog signal by amplifying the first through third pattern signals to have a certain magnitude ratio and synthesizing the amplified first through third pattern signals into the RF analog signal, where “n” is an integer of at least 3, may be provided.