Speed-up charge pump circuit to improve lock time for integer-n or fractional-n gsm wireless data/voice applications

Abstract

A system and method for speed-up of the frequency switching time of a circuit, generally a voltage controlled oscillator having an operating frequency controlling input terminal. A first control circuit is coupled to the frequency controlling input terminal for maintaining the operating frequency of the oscillator at its first selected operating frequency. Circuitry is provided which is responsive to a directed change from the first operating frequency of the oscillator to a second different operating frequency of the oscillator to apply a voltage to the input terminal determined by the size of the directed change in the operating frequency and for a predetermined time period. This circuitry includes a switch coupled to the input terminal, a charge pump coupled to the switch and remote from the input terminal and a timer controlling the current output of the charge pump and the switch. The output of the charge pump is a current which is converted to a voltage. The system further includes a digital signal processor responsive to the amount of change of operating frequency for controlling the amount of current in a range manner provided by the charge pump and for controlling the time period of application of the current to the circuitry for converting the current to a voltage. The circuitry for converting said current to a voltage is an RC circuit which includes a resistor in parallel with a capacitor.