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The switching-capacitor current-reused LC-VCOs with degeneration resistors and capacitors have been presented in this article. Two switching-capacitor current-reused LC-VCOs are designed and measured. One uses one set of switching capacitor. The other uses two sets of switching capacitors. The former divides the frequency band into two sub-bands. However, the latter divides the frequency band into four sub-bands. The proposed VCOs reuse the dc current and have lower power consumption as compared with those of conventional VCO topologies. The usage of two degenerated resistors at the source terminals of NMOS and PMOS transistors enhances the characteristics of symmetry of differential outputs. The topology of switching capacitor results in smaller KVCO by dividing the wanted frequency range into two sub-band or four bands. Hence, the phase noise is indeed improved. The proposed current-reused LC-VCO is designed for applications on the communication systems operating at the frequencies from 2.3 to 2.7 GHz. For the VCO with two sub-bands, measured phase noise characteristics show À106.65 and À123.65 dBc/Hz at 100 kHz and 1 MHz offset from 2.38 GHz, respectively at a consumption current of 3 mA from a 1.8 V supply. The output power is up to 3.6 dBm. For the VCO with four sub-bands, measured phase noise characteristics show À104.85 and À124.6 dBc/Hz at 100 kHz and 1 MHz offset from 2.359 GHz, respectively at a consumption current of 2.6 mA from a 1.8 V supply. The output power is up to 4.14 dBm. The research results show that the phase noise characteristics are good by dividing the frequency band into multiple subbands and then reducing KVCO. ACKNOWLEDGMENTSThis work is supported by the National Science Council in Taiwan. The project contract number is NSC96-2220-E-022-001. The authors thank the Chip Implementation Center (CIC) of National Science Council, Taiwan, ROC, for the support of the TSMC CMOS processes. SCALEABLE COMPREHENSIVE LOW-NOISE PHEMT MODEL THAT PREDICTS IP3 AND NOISE

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