Bandwidth Extension of CMOS Amplifier Using Mutually Coupled Three-Inductor Coil

This brief introduces a mutually coupled three-inductor (MCTI) coil in the stacked structure, where an additional winding is incorporated into a conventional T-coil, producing supplementary self-and mutual inductances. This addition provides enhanced design flexibility and improves the performance in bandwidth extension for CMOS amplifiers. Moreover, the supplementary mutual couplings enable a smaller self-inductance for bandwidth extension, resulting in a reduction in overall coil size and parasitic resistances. A four-stage amplifier incorporating MCTI coil peaking has been designed and fabricated using a 28 nm FD-SOI CMOS process. Measurements show a dc gain of 12.2 dB, a 3-dB bandwidth exceeding 50 GHz, and a power consumption of 23.75 mW. It also exhibits improved eye performance with a modest overshoot for 28 Gbps NRZ input, achieving peak-to-peak jitter as low as 5.0 ps.