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Abstract

A system, method, and apparatus for generating a low noise bias current to improve jitter performance in a wide frequency range LC-based phase-locked loop (PLL) circuit for multi-speed clocking applications. A plurality of noise-reducing stages are coupled in series and disposed between a power supply and a voltage controlled oscillator (VCO) including: a first stage VCO regulator; and a second stage bias circuit having a plurality of PMOS transistors cascode-coupled to each other and optionally grouped into one or more parallel branches of cascode-coupled transistor pairs. Each branch can be automatically enabled by a calibration code based on the desired reference clock signal in order to provide a wide range of currents to the voltage controlled oscillator. The cascode coupled pair includes a bias transistor coupled in series with a self-biased current buffer to provide high output impedance with minimal current change for any input voltage change from noise.

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