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AUTOMATIC MULTIDROP 5 MHz REFERENCE PARASITIC LOAD COMPENSATION NETWORK

IP.com Disclosure Number: IPCOM000008138D
Original Publication Date: 1997-Jun-01
Included in the Prior Art Database: 2002-May-21
Document File: 4 page(s) / 107K

Publishing Venue

Motorola

Related People

James K. Gehrke: AUTHOR [+2]

Abstract

Modem wireless communications base stations often require an external high stability frequency reference. This external frequency reference can be used to provide the reference signal for a number of base stations. Normally the output signal is routed to each base station through a star configuration of distribution amplifiers. Many communication system base stations were originally designed to receive this external, typically 1 to 10 MHz, frequency reference input with a 50 Ohm imped- ance interface, but to reduce distribution amplifier cost and improve reliability, a single 50 Ohm output source can be used to drive a rack of up to 8 base stations. To do this the input buffers on the base sta- tions that receive the reference signal are changed to high input impedance amplifiers with the stations configured in a series connection with a 50 Ohm endpoint termination. There remains a signal load- ing issue with high values of shunt parasitic capaci- tance. The problem was to find a way to tune out this parasitic capacitance when the number of sta- tions connected can be varied from 1 to 8.

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m MOlVROLA Technical Developments

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AUTOMATIC MULTIDROP 5 MHz REFERENCE PARASITIC LOAD COMPENSATION NETWORK

by James K. Gehrke and Gregory A. Alms

BACKGROUND

  Modem wireless communications base stations often require an external high stability frequency reference. This external frequency reference can be used to provide the reference signal for a number of base stations. Normally the output signal is routed to each base station through a star configuration of distribution amplifiers. Many communication system base stations were originally designed to receive this external, typically 1 to 10 MHz, frequency reference input with a 50 Ohm imped- ance interface, but to reduce distribution amplifier cost and improve reliability, a single 50 Ohm output source can be used to drive a rack of up to 8 base stations. To do this the input buffers on the base sta- tions that receive the reference signal are changed to high input impedance amplifiers with the stations configured in a series connection with a 50 Ohm endpoint termination. There remains a signal load- ing issue with high values of shunt parasitic capaci-

tance. The problem was to find a way to tune out this parasitic capacitance when the number of sta- tions connected can be varied from 1 to 8.

PRINCIPLE OF OPERATION

  'The idea is to resonate out the signal loading of the parasitic shunt capacitance of different numbers of base stations within the site reference without the need for operator initialization or prior...