Design, Realization, and Simulation of CMOS Active Inductors for RF Applications

Many Radio frequency (RF) circuits such as low noise amplifier (LNA), voltage controlled oscillators (VCO), and RF filters need inductors for realization. Passive and spiral implementations of the inductors have many limitations, especially when these RF circuits are designed and realized as an integrated circuit. Standard structures realize active inductors that usually provide a limited inductor value and quality factor. This paper presents an alternative active Complementary Metal-Oxide Semiconductor (CMOS) realization, based on the use of the gyrator-c configuration that is suitable for the Integrated Circuit (IC) fabrication. Four CMOS active realizations are presented that include the basic realization, topology with feedback resistor, active MOS transistor feedback, and the voltage divider type structure. A comparative study between these realizations is performed to improve the active filter performance. The most important parameters that have to be investigated are the quality factor, range of inductors value at specified operating frequency, and the self-resonance frequency. It is shown that the use of passive feedback improves the active inductor performance, however, large passive resistance is required which is not suitable for the IC fabrication. An alternative MOS transistor and the voltage divider are used to replace the passive feedback resistor, so as to improve the performance without the need of a large chip area for fabrication. It is also shown that different transistor dimensions w1,w2,… and different current source values I1, I2 result in different performance parameters. Therefore, minimized transistors dimensions are required for the minimum chip area, and minimized current values are required to minimize the power consumption. It is shown that the voltage divider AI realization resulted in a significant improvement in inductance value (L=20.16 nH) and a higher quality factor (Q=3.069) as compared to other topologies.