Bandwidth Enhancement of On-Chip Transformers Using Negative Capacitance

This brief presents a novel technique for bandwidth enhancement of on-chip transformers using the negative capacitance (NCAP) circuit. Since the coupling capacitance between the primary and secondary windings of an on-chip transformer limits its operating bandwidth, floating NCAP is added to compensate for the effect of the coupling capacitance on the transformer's performance. Fabricated in a 0.13-μm complementary metal-oxide-semiconductor technology, the 4 : 4 on-chip transformer with NCAP exhibits a wideband frequency response with 1.6 dB added gain compared with the transformer without NCAP. In addition, the input and output return losses (
S
₁₁
and
S
₂₂
) values are well below -10 dB over the bandwidth for the transformer with NCAP.