US Patent 7974374 Multi-mode VCO for direct FM systems

Systems for multi-mode phase modulation are disclosed. Systems provide for direct modulation of a multi-mode voltage controlled oscillator (VCO). A fractional-N counter may be used in a phase-locked loop (PLL) to synthesize a radio frequency carrier signal. The multi-mode VCO may be characterized by a first frequency gain during operation in a first mode and by a second frequency gain during operation in a second mode where signals controlling the first and second operating modes are provided by a control circuit. The control circuit may include a switch to provide control signals to the VCO.