Mojtaba Sadeghi - Department of Electrical Engineering, Shiraz Branch,Islamic Azad University ,Shiraz, Iran
Abbas Kamali - Department of Electrical Engineering, Fasa Branch,Islamic Azad University ,Fasa, Iran
Seyed Mohammad Sadegh Hashemi Nassab - Ph.D student of Islamic Azad University Fasa, Iran

Oscillators are circuits that requires no input signal, produced of output signal. These circuits in the signal generation sources, used In various applications such as, communication circuits, digital systems and controls, watches, computers, medical equipment, etc. in order to provide frequency that determine accuracy time. In many application circuit, oscillator used should be adjustable, the output frequency is a function of an input signal (usually a voltage). This type of oscillator Called voltage controlled oscillator (vco).In this paper represents a new enhanced Colpitts oscillator, which is designed based on gm-boosting of a conventional Colpitts oscillator. The proposed topology increases the negative resistant and enhances the startup difficulty of the conventional Colpitts oscillator. This enables the Colpitts oscillator to operate in low-power consumption. The proposed circuit is designed using 0.18 μm technology and is simulated under 1.8V supply voltage the operating frequency is 1 GHz in software advanced design system (ADS). Simulations show the output phase noise of -135.8 dBc/Hz at 1MHz offset frequency when the operating frequency is 1 GHz

Colpitts oscillator, gm-boosting, voltage controlled oscillator (vco), oscillation frequency, phase noise