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Check the paper that is attached. It describes frequency synthesizer and you can see how the vco is designed.
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TITLE: A low jitter 0.3-165 MHz CMOS PLL frequency synthesizer for 3 V/5 V operation
ISSUE: IEEE Journal of Solid-State Circuits, vol. 32, pp. 582 - 586, April 1997
AUTHORS: Howard C. Yang, Lance K. Lee, and Ramon S. Co
This paper describes a phase-locked loop (PLL)- based frequency synthesizer. The voltage-controlled oscillator (VCO) utilizing a ring of single-ended current-steering amplifiers (CSA) provides low noise, wide operating frequencies, and opera- tion over a wide range of power supply voltage. A programmable charge pump circuit automatically configures the loop gain and optimizes it over the whole frequency range. The measured PLL frequency ranges are 0.3-165 MHz and 0.3-100 MHz at 5 V and 3 V supplies, respectively (the VCO frequency is twice PLL output). The peak-to-peak jitter is 81 ps (13 ps rms) at 100 MHz. The chip is fabricated with a standard 0.8-µm n-well CMOS process.
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Good luck!
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