A Distributed Amplifier Based Active Transversal Filter Mmic with Positive and Negative Adjustable T a . Weights for Very High Speed Lightwave Systems

A distnbuted amplifier based 5-tap tramversai filter using MESFET implementation of the Gilbert Cell as the tap weights has been designed for use as a fractonally spilfed adjustable equaluer in high speed optical c~mmunication systems. The effective tramconductance of the Gilbert Celi can be adjusted h m negative to positive values and therefore the transversal filter designed has adjustable positive and negative tap weights. With these tap weight variation capabilities the fkquency response of the filter can be significantly altered makùig it an attractive candidate for adaptive pulse shaping in optical receivers. This is the fiist t h e a transversal fiiter with adjustable positive and negative has k e n implemented. in this thesis a review of intensity modulatioa/direct detection @I/DD) optical communications is provideci with an emphasis placed on the requirement for adaptive Iinear equaiization using the transversal filter. The £idamentai theory behind the transversal fZ1ter in then presented. Next, the design techniques used in order to achieve a transversal fiiter with positive and negative adjustable tap weights are discussed. These include a discussion of the transversal fiiter building blocks: the distributed amplifier, lumped element aaincial eaasmission lines and the Gilbert Ceii. Once the building blocks are outlined the entire transversal filter MMIC design is introduced. Finally, simulateci and measured fkquency response and transient response resdts are presented for various tap weight configurations. Frequency response resuits demonstrate the transversal nIter is capable of achieving a variety of filtering fiuictions. Transient response results demonstrate the transversal flter's ability to alter the pulse shape in a 2.5Gbls system.