A wideband dual-mode VCO with analog and digital automatic amplitude control circuitry

In this paper, a dual mode class-C LC voltage controlled oscillator (VCO) has been designed in a 0.18 μm CMOS process. This system is capable to oscillate at two different frequencies, achieving a quite wide 64% tuning range. Depending on the oscillation frequency, the VCO current consumption is automatically adjusted from 4-5.5 mA using a 0.9 V power supply. The phase noise at 1 MHz offset from the carrier frequencies of 2 and 3 GHz are also -125 and -122 dBc/Hz, respectively. A design formula for the tuning range is proposed which considers the ratio of frequency overlap (OL) and all the parasitic effects from band-switching capacitor array and transistors. Furthermore, in order to stabilize the performance through the mentioned tuning range, both analog and digital automatic amplitude control techniques are presented. These amplitude control schemes consume a negligible power and area without degrading the phase noise.