Feature: RF and microwave


element direct-RF-sampling reference architecture developed by Analog Devices. Its detailed signal integrity analysis revealed that clock spurs originate from the integrated ADF4382 PLL/VCO IC (Figure 1), with radiative coupling mechanisms introducing periodic interference into the DAC output traces. Such coupling not only produced coherent spectral artefacts, but it affected system-level linearity and multi-channel synchronisation. To address these concerns, a comprehensive mitigation


methodology was used, combining physical and digital measures. On the hardware side, enhanced electromagnetic shielding improved ground isolation, and PCB layout optimisation minimised radiative and conductive coupling between the high frequency clock networks and analogue signal paths. Complementing these measures, a precise digital phase-calibration algorithm was introduced to de-correlate residual spurious components, effectively suppressing any remaining coherent clock feed-through. Tis hybrid approach – integrating robust hardware shielding


Reducing clock spur interference in phased array subsystems


By Siddhartha Das, System Applications Engineer, Analog Devices


M


aintaining exceptional signal purity in high-performance RF systems is essential, to ensure accurate signal representation and optimal dynamic range. Among the many significant threats to affecting that signal, and thus system performance, are


clock spurs. Tese are unwanted tones resulting from clock leakage or coupling into sensitive analogue signal paths. Clock spurs elevate the noise floor, reduce spurious-free


dynamic range (SFDR) and compromise overall signal integrity, particularly in direct-RF-sampling architectures where the clock and data domains are tightly integrated. Here’s an example: Quad-Apollo MxFE (mixed-signal front end) is an X-band digital beamforming platform, utilising an every-


36 April 2026 www.electronicsworld.co.uk


with intelligent digital correction – significantly reduced clock spur levels, restoring SFDR performance and ensuring stable, deterministic operation across all JESD204C data links. Te resulting improvements underscore the importance of system-level mitigation strategies in achieving ultra-clean spectral performance in next-generation high-speed RF platforms.


High level procedure Te spur de-correlation methodology in the Quad-Apollo MxFE platform integrates both physical mitigation and algorithmic calibration techniques, to systematically eliminate clock-induced spectral artefacts. Tis structured process ensures that all data converters operate coherently whilst minimising interference from coupled clock energy. Te approach can be broken down into the following key stages:


Spur identification: Te process begins by isolating the specific clock spur or harmonic that most significantly impacts overall system performance. Spectral analysis tools are used to measure spur levels at various operating conditions, identifying the dominant contributor to SFDR degradation.


Phase rotation: Once the critical spur is identified, controlled phase adjustments are applied to the sample clocks of selected phase locked loop (PLL) ICs, whilst one device remains fixed as the timing reference. Tis controlled phase rotation enables the characterisation of spur behaviour as a function of relative clock phase.


Spur monitoring: As phase offsets are introduced, the system continuously monitors the resulting spur magnitude using spectral measurements or FFT- based evaluation. By mapping spur amplitude against clock phase, the configuration yielding the lowest spur power can be precisely identified.


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