CMOS THz Modeling 61
Figure 3.20: Causality verification by Hilbert transformation: error
magnitude comp arison of S21.
3.5 Conclusion
An a ccurate device model is critical for CMOS-based THz circuit design. Since
transmission line (T-line) is one of the most fundamental passive device com-
monly used in the THz circ uit design; an in-depth study of T-line model at
THz is thereby important. Note that dispersion and non-quasi-static effects
are difficult to be modeled by traditiona l methods such as the integer-order
RLCG model with causality. By the proposed compact and causal fra ctional-
order T-line model, the causality concern is resolved for T-line by consid-
ering the frequency-dependent dispersion loss and non-quasi-static effect a t
THz. The mea sured results have confirmed that the proposed fractional-order
RLGC T-line model and CRLH T-line model have improved accuracy over the
traditional integer-order models from mm-wave to THz region. Accordingly,
the proposed fractional-order T-line models will be applied in the design for
CMOS-based THz circ uits in the following sections.
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