Phase-locked loop having a stable damping factor

US6556088B1 · kind B1 · utility

Assignee

• TEXAS INSTRUMENTS DEUTSCHLAND GMBH · DE

Inventors

• Markus Dietl · Munich, DE
• Hermann Seibold · Alzenau, DE

Key dates

• Filing date: Oct 12, 2000
• Grant date: Apr 29, 2003
• Expiry date: Oct 12, 2020

Classification

• Technology area (CPC H): Electricity
• CPC primary: H03L2207/04
• WIPO field: Basic communication processes
• WIPO sector: Electrical engineering

Abstract

A phase-locked loop (PLL) has a phase detector coupled to an output of the PLL and to a reference signal and a low pass filter including a first and a second charge pump coupled to an output of the phase detector. A capacitor is coupled to an output of the first charge pump, a first bias circuit coupled to the capacitor, the first bias circuit having a differential output. A voltage controlled ring oscillator has a plurality of differential inventer stages, each having a first input coupled to a first output of the first bias circuit and a second input coupled to a second output of the first bias circuit. A second bias circuit is coupled between the capacitor and the first bias circuit, an output of the second bias circuit being coupled to an input of the first bias circuit and to an output of the second charge pump. The PLL circuit exhibits a stable damping factor with respect to frequency.