High-accuracy electromagnetic analysis method for differential circuits with discontinuities

Abstract This paper presents a high-accuracy electromagnetic (EM) analysis method for differential circuits that accurately considers the effects of structural discontinuities. Discontinuities at interfaces between components—such as MOSFETs with ground planes and transformer-based matching circuits without ground planes—introduce boundary mismatches that degrade EM analysis accuracy in high-frequency designs. To address this problem, a divided EM analysis method incorporating a four-port de-embedding technique is developed to account for discontinuities in both even and odd modes. The validity of the proposed method is demonstrated through the design of a twos-tage differential amplifier, where the error in the odd-mode gain Soo21 is reduced from 0.20 dB to 0.01 dB at 106 GHz. The method enables computationally efficient and highly accurate EM analysis without requiring full-structure EM analysis.