Octagonal Phase Rotator Circuit for Low-Jitter Phase Updates
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Solution Overview
Problem
Octagonal phase rotators suffer from glitching transients during phase updates, causing systematic jitter due to polarity switches in the IQ-DAC activating at quadrant crossings.
Innovation Solution
The octagonal phase rotator apparatus includes I-mixer, Q-mixer, and IQ-mixer units with polarity switches controlled separately by different I-DAC or Q-DAC control bits, reducing glitching transients by staggering switch times at quadrant crossings, and utilizing an array of unit cells to minimize transistor size and operational requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If polarity switches in the IQ-DAC are activated at quadrant crossings to enable phase rotation, then phase adjustment capability is improved, but glitching transients are generated causing systematic jitter
Solution Approach 1:
The patent divides the single IQ-DAC into multiple parallel IQ-DAC components (first IQ-DAC component, second IQ-DAC component, etc.). Each component handles a portion of the current steering function, and their polarity switches are controlled independently. This segmentation allows the system to maintain phase adjustment capability while distributing the switching events across multiple components, thereby reducing glitching transients and improving signal stability.
2Device complexity
If all IQ-DAC components use the same control bits for polarity switching, then device complexity is reduced, but glitching transients occur at quadrant crossings
Solution Approach 1:
The patent implements dynamic control of polarity switches in different IQ-DAC components by assigning different control bits to each component. The first IQ-DAC component's polarity switches are controlled by first I-DAC control bits and first Q-DAC control bits, while the second IQ-DAC component's polarity switches are controlled by second I-DAC control bits and second Q-DAC control bits. This dynamic differentiation eliminates simultaneous switching events at quadrant crossings, reducing glitching transients while maintaining manageable device complexity through systematic control bit assignment.
Data Source
AI summary
Octagonal phase rotator includes an I-mixer having an I-DAC for steering current between positive and negative phases of an in-phase signal depending on k I-DAC control bits of a control code, a Q-mixer having a Q-DAC for steering current between the positive/negative phases of a quadrature signal depending on k Q-DAC control bits of the code, and an IQ-mixer having n IQ-mixer units each comprising an IQ-DAC for switching a second current unit between the in-phase and quadrature signals, in dependence on a respective bit of n IQ-DAC control bits, and between the positive/negative phases of the in-phase and quadrature signals via I and Q polarity switches respectively of that component. I and Q polarity switches of some different IQ-DAC components switch depending on different I-DAC control bits and Q-DAC control bits respectively. A summation circuit sums weighted output signals from the mixers to produce an output signal of phase.