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A 5 GHz voltage controlled ring oscillator (VCO) has been designed using 0.18 /spl mu/m CMOS technology. Source Capacitively Coupled Current Amplifier (SC3A) is adopted to realize this VCO. Because of the band-pass characteristic of the SC3A, this VCO exhibits the low noise performance with a large tuning range. It can operate from 4.3 GHz up to 6.1 GHz with a phase noise of about -85 dBc/Hz at 1 MHz frequency offset. For the 2 V supply voltage, the power consumption is about 80 mW.