High-Quality-Factor Active Capacitors for Millimeter-Wave Applications

This paper presents single-ended and differential configurations of active capacitors that exhibit high-quality (Q) factor at millimeter-wave frequencies. Both structures provide a small tunable negative resistance that can be exploited to compensate for the loss of other components, such as inductors in millimeter-wave integrated circuits. Unlike passive capacitors, which exhibit increasing capacitance with frequency (due to the inductive parasitic), the proposed active capacitors display relatively frequency-independent values. Fabricated in 0.13-μm IBM CMOS, tunable Q values of more than 20 are obtained at 60 GHz. A 40-GHz bandpass filter is designed and fabricated using the single-ended active capacitor cells in a 0.13-μm IBM CMOS process exhibiting 0-dB insertion loss.