Invention Grant
US08344812B2 Loop filter and voltage controlled oscillator for a phase-locked loop 有权
用于锁相环的环路滤波器和压控振荡器

Loop filter and voltage controlled oscillator for a phase-locked loop
Abstract:
A phase-locked loop includes a loop filter and a voltage controlled oscillator (VCO). The VCO includes multiple transistors, each transistor having a smaller transconductance (gm) than if a single transistor were used while maintaining the same loop bandwidth and drain-to-source current through the transistor. As a result of a smaller transconductance in the VCO, a larger resistor can be used in the loop filter without increasing the noise. With a larger resistor, a smaller capacitor can be used in the loop filter as well. Alternatively, the transconductance can be reduced by a certain factor and the resistance value can be increased by the same factor to maintain a constant loop bandwidth but with a reduction in the amplitude of the noise. Thus, a smaller loop filter capacitor can be achieved albeit with the same noise level, or a lower noise level with the same size capacitor for the loop filter.
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