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A new differential delay cell with a complementary current control to increase the control voltage range as well as the operation frequency is proposed for low-voltage operation. The new differential delay cell is employed in a four-stage voltage-controlled ring oscillator (VCRO). The VCRO is implemented using 0.18 m 1P6M CMOS process and 1.8 V supply voltage. Measured results show that a wide operation frequency range from 5.36 to 3.03 GHz is achieved for the full range control voltage from 0 to 1.8 V. Measured phase noise is 107 dBc/Hz at 1 MHz offset from the 5.22 GHz centre frequency.