30 GHz SiGe active inductor with voltage controlled Q

• Published in: Integration (Amsterdam) 2021-03, Vol.77, p.13-24
• Main Authors: Torres, Jorge Alves, Freire, J. Costa
• Format: Article
• Language: English
• Subjects: Active filter; Active inductor; Cascode gyrator; Negative resistance; SiGe technology
• ISSN: 0167-9260; 1872-7522
• DOI: 10.1016/j.vlsi.2020.11.003

An active inductor (AI) based on a cascade gyrator for 30 GHz applications implemented with a 0.25 μm in SiGe technology is presented. The gyrator converts not only a key capacitor into an inductor, but also an added resistor, into a negative resistor. This gyrator-RC has its losses compensated by the negative resistor improving the active inductor Q factor. Changing the bias voltage and current allows to obtain a variable AI. A study of a cascade gyrator AI topology is done to understand the circuit behavior and key elements. For this purpose, an AI impedance model is introduced and discussed. An improved AI with the added resistor replaced by a voltage controlled mosfet resistor is proposed. This extra control voltage allows the variable AI quality factor fine tuning. Schematic and circuit extracted from layout simulations are presented, and compared with the measured results of two prototypes of the AIs (one with a fixed resistor and other with a voltage controlled resistor). A prototype of a high pass filter using the AI with fine Q control was fabricated. Non-linear simulations for different input signal levels were performed and compared with measurements. Also discussion on the non-linear models accuracy is performed.