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An enhanced LC resonator has been implemented in a voltage controlled oscillator (VCO) in the PLL (phase locked loop) for an ASK (amplitude shift key) UHF receiver IC chip. With the enhanced resonator, the VCO obtains a high Q quality, and it can realize a phase noise figure less than -99.7dBc/Hz at 100 kHz-offset frequencies from a 433MHz carrier. Compared with the traditional LC resonator VCO, its phase noise has dropped more than 3dBc/Hz. Consisting of only a few active devices, the VCO has very low power dissipation and a low cost. The on-chip PLL performs the LO (local oscillator) generation, through which the receiver can work at ISM band frequencies from 290 MHz to 470 MHz. The VCO presented in this paper has a tunable frequency over 290-470 MHz under control voltage from 1V to 5V, with an output power of 2.20-2.30dBm.