Dual-loop phase-locked loop

US5854575A · kind A · utility

Assignee

• LSI Logic Corporation · US

Inventors

• Alan Fiedler · Marlborough, US
• Daniel J. Baxter · Stanley Corners, CA

Key dates

• Filing date: Nov 13, 1997
• Grant date: Dec 29, 1998
• Expiry date: Nov 13, 2017

Classification

• Technology area (CPC H): Electricity
• CPC primary: H03L7/1075
• WIPO field: Basic communication processes
• WIPO sector: Electrical engineering

Abstract

An integrated circuit phase-locked loop includes a phase/frequency detector, a charge pump, and a voltage-controlled oscillator (VCO) which are coupled together in series. The VCO has first and second VCO control inputs, and has a VCO output which is coupled to the phase/frequency detector. An off-chip loop filter input is coupled between the charge pump and the first VCO control input for coupling to an off-chip loop filter. An on-chip loop filter is coupled between the first VCO control input and the second VCO control input. The VCO has a lower voltage-to-frequency gain from the first VCO control input to the VCO output than from the second VCO control input to the VCO output.