On a class of cross coupled fully differential filters

Abstract

In this paper, a class of cross-coupled differential filters is presented. The filters implemented are second order, using two transistors cross-coupled surrounded by passive RLC components. The input of each filter is differential and so is its output. Biasing of each filter is straightforward, and the stability of the filters is examined. Several of the filters were built experimentally using discrete components and simulated using SPICE in a 0.18 μm Taiwan Semiconductor Manufacturing Company (TSMC) complementary metal-oxide semiconductor (CMOS) process, confirming the validity of the filters.

Single transistor RC‐only second‐order allpass filters

“…2,3 However, allpass filters reported in the literature are predominantly LC filters that are either purely passive 2 or require many transistors, such as the bipolar transistor-based design in Ulusoy et al 1 Since using allpass filters to replace digital delay stages significantly reduces the hardware complexity and cost, 3,4 designing allpass filter cells in current and voltage modes using single transistors has been attempted in Ahmadi et al 5,6 with excellent performance being achieved at RF frequencies. Fully differential allpass filter cells were also recently reported in Elamien et al 7 and in Maundy et al 8 among other types of filters. It is again noted that all of the thus far reported second-order single transistor filters have been LC-type filters with at least one inductor required.…”

“…In this letter, we attempt to explore the possibility of obtaining RC second‐order allpass filters using a single transistor surrounded by four impedances in a common‐source topology. The automated search procedure is based on the two‐port network modeling as explained in detail in Maundy et al This procedure has proven its success in facilitating the search for circuits that satisfy a certain design criteria based on predefined circuit structure using the strength of symbolic mathematics tools …”

Minimal two‐transistor multifunction filter design

“…Together with Elwakil and Maundy and Maundy et al . , this work adds to the incomplete body of knowledge on filter design with single transistors.…”

“…Such filters benefit from the recent advances in realizing on chip transformers . Fully differential filters using two cross‐coupled transistors were also systematically designed and verified for the first time in while one of the filters derived in was transformed into an all‐pass filter for beam‐forming applications in .…”