Archive for February 13, 2012

Tutorial on Passive Filters, Data Transmission and Equalization

EyeDiagram

In this episode Shahriar explores the world of filters! Starting from a simple lumped RC filter, he briefly covers the theory before moving onto measurement techniques. The bandwidth of the filter is verified experimentally in the time domain. A more complex RLC band-stop filter is also demonstrated with a tune-able inductor which is measured using an RLC meter. Using a Rigol spectrum analyzer with built in tracking generator and an active probe, the frequency response of the filter is measured. Several other packaged filters are also demonstrated and a microwave band-pass filter is disassembled to reveal its internal construction. 

Moving onto “undesired filters”, a Tyco backplane board is presented and the bandwidth limitation of the backplane traces are measured. A Xilinx FPGA board equipped with a Virtex II PRO is used to generate a 1.5Gbps PRBS data stream through the Tyco board. After observing the frequency composition of the date, pre-emphasis equalization is used to compensate the backplane frequency limitations. Eye diagram measurements verify the benefit of pre-emphasis equalization to combat inter-symbol-interference (ISI).

I would like to acknowledge my friend and colleague, Dr. Timo Pfau for his expertise in setting up and configuring the Xilinx FPGA board.