A regulated low phase noise differential colpitts VCO for mobile RFID system

A regulated low phase noise differential colpitts VCO (voltage controlled oscillator) for mobile RFID system is presented. The differential colpitts VCO meets the multiple- interrogator environment specifications. The VCO use a 0.35 mum technology and achieves tuning range 1.55 GHz - 2.053 GHz. Measuring 910 MHz frequency divider output, phase noise performance is -106 dBc/Hz and -135 dBc/Hz at 40 kHz and 1 MHz offset, respectively. 5-bit digital coarse-tuning and accumulation type MOS varactors allow for 28.2% tuning range, which is required to cover the LO frequency range of a UHF Mobile RFID system. Optimum design techniques ensure low VCO gain (< 45 MHz/V) for good interoperability with the frequency synthesizer. To the author´ knowledge, this differential colpitts VCO achieves a figure of merit (FOM) of 1.93 dB at 2-GHz band.