Phase-locked loop with variable parameters

Abstract

An electronic system such as a processor or computer system includes a phase-locked loop (PLL) having a PLL parameter modification circuit. In one embodiment, the PLL parameter modification circuit may be programmed to provide one of several current control signals to a charge pump. Additionally, the PLL parameter modification circuit may be programmed to alter a loop filter transfer function by selectively changing resistance and/or capacitance values of the loop filter. Each current control signal modifies the charge pump output control voltage to a VCO differently, and, thus, modifying the current control signals to the charge pump effectively modifies the bandwidth of the PLL. In one embodiment, the PLL parameter modification circuit modifies current control signals to the charge pump by selectively inserting and removing, in accordance with programmable register bit(s) states, diode configured transistors in a current mirror configuration. Thus, a ratio of the output current of the current mirror i.e. the current control signals, to a current reference signal may be programmably modified to modify the bandwidth and lock time parameters of the PLL. The PLL parameter modification may modify the resistive and capacitive parameters of the loop filter by selecting configuring multiple resistors and capacitors to form one of many equivalent circuits.