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.