A differential common drain Colpitts VCO circuit suitable for sub-1V low phase noise

Abstract

This letter proposes a differential common drain Colpitts VCO circuit suitable for low phase noise oscillation at the sub-1V supply voltage. Oscillation with low phase noise at the sub-1V supply voltage is facilitated by employing inductors as the current sources of the proposed circuit. One of the two feedback capacitors in the half circuit of the proposed VCO circuit is replaced by a MOS varactor in order to further increase negative resistance. Post-layout simulation results using a 0.18 μm RF CMOS technology show that the phase noise performances of the proposed circuit at the sub-1V supply voltages are much better than those of the well-known cross-coupled VCO at the same supply voltages. Keywords: VCO, Colpitts VCO, sub-1V Classification: Integrated circuits Lett., vol. 19, no. 9, pp. 566-568, Sept. 2009. [5] T. H. Lee and A. Hajimiri, "Oscillator phase noise: a tutorial," IEEE J. Solid-State Circuits, vol. SC-35, no. 3, pp. 326-336, March 2000. [6]

Sub-1 V <i>V</i>-<i>I</i> converter-based voltage-controlled oscillator with a linear gain characteristic

“…To facilitate these characteristics of the PLL, the voltage-controlled oscillator (VCO) must operate within a wide range of tuning frequencies and a narrow range of control voltages (V ctrl ). In other words, the VCO must have the following characteristics: a wide range of operating frequencies, linear voltage-to-frequency VCO gain (K VCO ) for a wide V ctrl range, low power consumption, a small area overhead, and high immunity to supply noise [6,7].…”