This paper presents a new design of low power voltage controlled oscillator (VCO) circuit using three transistors NOR-gate and I-MOS (inversion mode) varactor tuning method. Variation in the oscillation frequency has been obtained by varying the output load capacitance with the use of I-MOS varactor tuning consisting of two PMOS transistors connected in parallel. Variable capacitance across the I-MOS varactor has been achieved by varying the source/drain voltage ([Formula: see text] and back-gate voltage ([Formula: see text]. Variation of [Formula: see text] from 1[Formula: see text]V to 2[Formula: see text]V provides the frequency deviation from 1.970[Formula: see text]GHz to 1.379[Formula: see text]GHz with I-MOS width of 8 [Formula: see text]m at power supply voltage ([Formula: see text] of 1.8[Formula: see text]V. Power consumption of the circuit is 1.296[Formula: see text]mW with [Formula: see text] of 1.8[Formula: see text]V. The results have been obtained for different I-MOS varactor widths like 5[Formula: see text][Formula: see text]m, 8[Formula: see text][Formula: see text]m and 10[Formula: see text][Formula: see text]m. Further, variations in the frequency have been obtained from 0.650 GHz to 2.584 GHz with the Vdd variation from 1[Formula: see text]V to 3[Formula: see text]V. In addition, by variations of [Formula: see text] from 0[Formula: see text]V to 1.8[Formula: see text]V and [Formula: see text] from 1[Formula: see text]V to 3[Formula: see text]V, the proposed oscillators operate in the frequency range from 0.556[Formula: see text]GHz to 2.584[Formula: see text]GHz for 8[Formula: see text][Formula: see text]m width of I-MOS varactor. Proposed VCO circuit show a phase noise of [Formula: see text][Formula: see text]dBc/Hz at 1[Formula: see text]MHz offset from the carrier frequency and the figure of merit (FoM) for the VCO is 154.51[Formula: see text]dB/Hz. Proposed VCO shows an improved performance in terms of power consumption, output frequency and FoM.
