AUTOMATIC MULTIDROP 5 MHz REFERENCE PARASITIC LOAD COMPENSATION NETWORK
Original Publication Date: 1997-Jun-01
Included in the Prior Art Database: 2002-May-21
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.