Polyphase RF-DAC Cell for Third-Order Harmonic Suppression
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Solution Overview
Problem
In mobile communication devices, RF digital-to-analog converters (RF-DAC) generate harmonic signals due to upconverting and amplifying baseband information, leading to third-order intermodulation distortion products that deteriorate the RF signal quality at the fundamental frequency.
Innovation Solution
An RF-DAC cell is configured to generate an RF output signal using a baseband signal and two local oscillator signals with different duty cycles, where the first signal toggles between predefined amplitude values and the second signal has a smaller duty cycle, reducing third-order harmonic content through polyphase mixing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If baseband information signal is upconverted and amplified using conventional RF-DAC, then RF signal power is delivered to antenna, but third-order intermodulation distortion products are generated that deteriorate RF signal quality
Solution Approach 1:
The conventional single-oscillator RF-DAC is segmented into a polyphase structure with multiple oscillators (first and second local oscillator signals) operating at different duty cycles. This segmentation allows the system to maintain high output power while distributing the mixing function across multiple phases, thereby reducing third-order intermodulation distortion products through phase diversity.
2Object-affected harmful factors
If conventional RF-DAC circuit is used, then device complexity is low, but RF signal quality deteriorates due to harmonic emissions
Solution Approach 1:
The patent merges multiple mixing functions into a unified polyphase RF-DAC architecture where first and second local oscillator signals with different duty cycles are combined to perform simultaneous upconversion and harmonic suppression. This merging approach achieves harmonic emission reduction while maintaining manageable device complexity through integrated circuit design.
3Power
If higher output power levels are used to improve signal delivery, then RF signal power increases, but third-order harmonic emissions increase proportionally
Solution Approach 1:
The patent employs periodic local oscillator signals with specifically designed duty cycles (first and second duty cycles) to control the mixing process. This periodic action with optimized timing characteristics enables the RF-DAC to deliver high output power while the duty cycle differentiation suppresses third-order harmonic emissions through constructive and destructive interference patterns.
Data Source
AI summary
An RF-DAC cell is configured to generate an RF output signal based on a baseband signal, a first signal and a second signal. The first signal has a first duty cycle and toggles between first predefined amplitude values, and the second signal has a second duty cycle smaller than the first duty cycle and toggles between second predefined amplitude values.