Abstract : This study was devoted to oscillator noise analysis and simulation in order to apply it on VCOs (Voltage Controlled Oscillator) for Intermediate Frequency integrated circuits, especially for TV receivers. An original period jitter transient simulation method, thanks to the transient noise simulator in ELDO and to a period extractor (ELDO-FAS based language software) has been worked out, making it is possible to deduce the VCO phase noise.With this kind of simulation, it is possible to evaluate the effect of the various noise sources in the VCO on the period jitter. Two VCOs, with optimized phase noise, have been designed for Intermediate Frequency integrated circuits. The first VCO, using a LC (inductance - capacitance) resonant architecture(the inductance is located outside the integrated circuit) has been designed and implemented. The frequency variation is produced by a variable capacitance. One of the major defects of the variable capacitor (parasitic phase displacement of the capacitive current) has been originally compensated. This VCO phase noise has been measured, simulated in many ways, with a good correlation. The period jitter simulation methodology has been so validated. A second VCO, of relaxation kind, completely integrated (it does not need any external element), dedicated to replace the first one, has been designed. Its architecture is based on RC (resistance - capacitance) elements in differential mode. It is able to operate with a low power supply (5V). Its phase noise has been optimized thanks to the previous methodology.