A complete study of the fault coverage achievable on two Radio Frequency (RF) Voltage Controlled Oscillators (VCO) is carried out. The peak-to-peak output voltage detection grants the maximal catastrophic and parametric fault coverage. The VCOs and the BIST (Built-In Self-Test) circuitry are designed using the STM CMOS 65 nm process. The frequency of oscillation is 3.6 GHz and the phase noise obtained at 1 MHz offset from the carrier is of −121.7 dBc/Hz for VCO1 and of −118.8 dBc/Hz for VCO2. The performances of the VCOs are simulated before and after the insertion of the circuitry for the BIST, in order to confirm the transparency of the BIST