Dynamic Analysis of OOK Modulators Using Eye Diagrams to Assess Data Rate and Output Matching

This paper presents a high-speed On-Off Keying (OOK) modulator in 65 nm CMOS, evaluated at data rates up to 50 Gbps. Eye diagrams are generated via a Hilbert transform from transient simulation data, enabling direct measurement of rise/fall times and eye openings at the modulator output. For 50 Gbps operation, the well-matched design achieves a rise time of 13.59 ps and a fall time of 17.95 ps, whereas the loosely matched design exhibits 25.34 ps and 28.00 ps, respectively. To assess the impact of communication-chain bandwidth, band-pass filters with 200 GHz, 150 GHz, and 100 GHz bandwidths—chosen based on covering the main lobe and varying extents of the side lobes—were introduced. As the bandwidth decreases, rise times for both matching conditions converge, reaching 35.47 ps (well-matched) and 34.72 ps (loosely-matched) at 100 GHz, suggesting bandwidth constraints dominate over matching. However, the fall time difference persists, with 21.44 ps and 24.24 ps at 100 GHz for well-matched and loosely matched cases, respectively, underscoring the importance of output matching. Additionally, the normalized eye height narrows more significantly in the loosely matched case.