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Fast-Hopping RF Synthesiser using Switched Charge-Pump Current for Optimum Channel-Dependent Noise Performance

IP.com Disclosure Number: IPCOM000021051D
Original Publication Date: 2003-Dec-18
Included in the Prior Art Database: 2003-Dec-18

Publishing Venue

Motorola

Related People

Authors:
Neil Turner

Abstract

The current state of the art in fast frequency-hopping synthesiser is to use a fractional-N core using a phase alignment system, switching to dual modulus after frequency and phase acquisition. This gives very rapid frequency change without the associated fractional-N spurious signals, by using a conventional dual-modulus system when locked. This paper shows how the use of a channel-dependent phase detector frequency can be implemented at no cost, to reduce in-band noise whilst still allowing the use of a simple, low-order loop filter. The key improvement is that the charge pump current can be set to optimise the locked performance. The phase detector frequency should be increased to as high a value as is feasible whilst still retaining an integer-N divide ratio. This dramatically improves the noise performance and is a significant improvement to the current state of the art.