Colpitts Oscillator Tutorial

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Colpitts Oscillator Tutorial
J P Silver E-mail: john@rfic.co.uk
1 ABSTRACT This paper will describe the design and test of a low noise VHF Colpitts voltage controlled oscillator (VCO), designed to operate at 200MHz (Tuning bandwidth of 23MHz/V over 1 to 10V ) with an associated phase noise performance of <-100dBc/Hz @ 10KHz. Theory will be given for the design of the reflection amplifier and high ‘Q’ resonator, together with the relevant CAD simulations to verify the design. 2 DESIGN DESCRIPTION 2-1 RESONATOR DESIGN [1,2] The first part of the design process is to determine the required unloaded Q of the resonator to achieve the phase performance of <-100dB/Hz at 10KHz. The simulation shown in Figure 1 simulates the phase noise of an oscillator for a given loaded Q, Noise fi