Design of Radio-Frequency Filters and Oscillators in Deep-Submicron CMOS Technology

Radio-frequency filters and oscillators are widely used in wireless communication and high-speed digital systems, and they are mostly built on passive integrated inductors, which occupy a relative large silicon area. This research attempted to implement filters and oscillators operating at 1-5 GHz using transistors only, to reduce the circuits’ area. The filters and oscillators are designed using active inductors, based on the gyrator principle; they are fabricated in standard digital CMOS technology to be compatible with logic circuits and further lower the cost. To obtain the highest operating frequency, only parasitic capacitors were used. Two new active-inductor circuits are derived from this research, labeled allNMOS and all-NMOS-II. The all-NMOS active inductor was used to design high-Q bandpass filters and oscillators, which were fabricated in TSMC’s 0.18-µm digital CMOS process. The highest center frequency measured was 5.7 GHz at 0.20-µm gate length and the maximum repeatably measured Q was 665. 2.4-GHz circuits were also designed and fabricated in 0.40-µm gate length. The all-NMOS-II circuit has superior linearity and signal fidelity, which are robust against process and temperature variations, due to its novel structure. It was used in signal drivers and will be fabricated in commercial products. Small-signal analysis was conducted for each of the active-inductor, filter and oscillator circuits, and the calculated performance matches those from simulations. The noise performance of the active inductor, active-inductor filter and oscillator was also analyzed and the calculated results agree with simulations. The difference between simulation and measured results is about 10% due to modeling and parasitic extraction error. The all-NMOS active-inductor circuit was granted a US patent. The US patent for all-NMOS-II circuit is pending. This research generated three conference papers and two journal papers