Duty cycle correction circuit for high speed interfaces
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Date
2026-02-11
Authors
Αντωνόπουλος, Νικόλαος
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Abstract
This MSc Thesis presents the design, implementation and evaluation of a low power and high accuracy duty cycle correction (DCC) architecture suitable for modern high speed and low voltage clocking systems operating at 2.5 GHz. The work is motivated by the limitations observed in the existing DCC solutions, which often struggle to simultaneously achieve high correction accuracy, wide input duty cycle range, low power consumption and robust operation across PVT variations. In high speed integrated systems, duty cycle distortion arises from multiple sources, including unequal rise and fall times in clock signals, device mismatch, asymmetric loading and variations introduced during clock generation and distribution. Such distortions can degrade the timing margins of sequential circuits and, more generally, negatively impact the performance of clock generation networks, making effective duty cycle correction a critical requirement for reliable system operation in advanced CMOS technologies. The proposed duty cycle correction architecture is designed to address these challenges by combining a simple yet effective topology with high operational robustness. The architecture employs an AC coupled input stage, a CML to CMOS conversion block to interface with standard CMOS logic and a feedback based duty cycle regulation loop that continuously corrects deviations from the ideal 50% duty cycle. A low pass filter is also used to stabilize the feedback mechanism and minimize oscillations. The design emphasizes minimal active components to reduce overall power consumption, while ensuring consistent performance across a wide input duty cycle range and under PVT variations. Circuit design is implemented using 65 nm CMOS technology provided by TSMC and the full design flow includes schematic capture, layout design and post layout verification. Post layout simulations demonstrate that the proposed DCC successfully corrects input duty cycles ranging from 30% to 70% to approximately 50%, with a maximum duty cycle output error of only ± 1.1% across all PVT variations. Moreover, phase noise analysis indicates minimal signal degradation, while Monte Carlo simulations confirm the circuit’s resilience against statistical variations and device mismatch. Compared to existing analog, digital and hybrid DCC architectures reported in the literature, the proposed design achieves a favorable tradeoff between power efficiency, operational frequency and robustness, making it highly suitable for multi GHz high speed interfaces and low power PLL networks.
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Keywords
Duty cycle corrector, 2.5 GHz, Process variations, PLL, Voltage variations, CML2CMOS convertion, Phase noise, Monte Carlo, Temperature variations