A 1 GHz dual-loop microprocessor PLL with instant frequency shifting

Increase in the speed of microprocessors and simultaneous reduction in power supply voltage have imposed more restrictions on the design of clock generators. They must now provide a low-jitter output in the presence of increasingly hostile power supply environments, larger frequency multiplication factors, and dynamic manipulation ofthe output frequency. This clock generator operates at 1.6-2.5V and is capable of providing up to 1GHz at 1.6V. A dual loop de-skewing architecture with in-loop dividers enables the microprocessor core to switch from 1 to 1/64 of the VCO frequency that is itself an integer multiple (e.g., 4/spl times/) of the external reference frequency.