Spannungsgesteuerter Oszillator mit automatischer Mittenfrequenzeinstellung

A voltage-controlled oscillator with automatic center frequency calibration. The frequency range (FOUT) of the oscillator is increased because of the presence of a switchable capacitor arrangement (SCA) which add or remove extra capacitors (XC1; XC2) in parallel with the variable capacitor (CV) of the resonant circuit (CV, L). Different voltage versus frequency characteristics (CHL, CHM, CHH) are so obtained. The control of the switchable capacitor arrangement is performed by a control signal provided (SC) by an oscillator control device (OCD). The control device also sends a reset pulse (RES) to a feedback device (FB) when a control voltage (VCTRL) reaches predetermined low (VTL) or high (VTH) voltage limits of the characteristics. With this reset pulse, the control voltage is reset to an intermediate voltage (VTM) in the middle of the range between the low and the high voltage limits. By resetting the control voltage, the output frequency is also brought to an average value, i.e. is centered. The voltage-controlled oscillator also preferably comprises a selection device (MX) adapted to immediately change the value of the control voltage to the intermediate voltage. The selection device operates faster than the feedback device. In a preferred embodiment, memory cells are provided to store control signals corresponding to different output frequencies, i.e. channels of a mobile telecommunication system such as the GSM. The stored control signals are applied to the switchable capacitor arrangement to improve the jump to a steady state of the voltage-controlled oscillator, e.g. starting from power-down.