A distributed amplifier-based active transversal filter MMIC with positive and negative adjustable tap weights for very high-speed lightwave systems

A distributed amplifier based 5-tap transversal filter using MESFET implementation of the Gilbert Cell as the tap weights has been designed for use as a fractionally spaced adjustable equalizer in high speed optical communication systems. The effective transconductance of the Gilbert Cell can be adjusted from negative to positive values and therefore the transversal filter designed has adjustable positive and negative tap weights. With these tap weight variation capabilities the frequency response of the filter can be significantly altered making it an attractive candidate for adaptive pulse shaping in optical receivers. This is the first time a transversal filter with adjustable positive and negative has been implemented. In this thesis a review of intensity modulation/direct detection (IM/DD) optical communications is provided with an emphasis placed on the requirement for adaptive linear equalization using the transversal filter. The fundamental theory behind the transversal filter is then presented. Next, the design techniques used in order to achieve a transversal filter with positive and negative adjustable tap weights are discussed. These include a discussion of the transversal filter building blocks: the distributed amplifier, lumped element artificial transmission lines and the Gilbert Cell. Once the building blocks are outlined the entire transversal filter MMIC design is introduced. Finally, simulated and measured frequency response and transient response results are presented for various tap weight configurations. Frequency response results demonstrate the transversal filter is capable of achieving a variety of filtering functions. Transient response results demonstrate the transversal filter's ability to alter the pulse shape in a 2.5Gb/s system.