Analysis of the Modified MOS Wilson Current Mirror A Pedagogical Exercise in Signal Flow Gr.pdfVIP

322 IEEE TRANSACTIONS ON EDUCATION, VOL. 44, NO. 4, NOVEMBER 2001 Analysis of the Modified MOS Wilson Current Mirror: A Pedagogical Exercise in Signal Flow Graphs, Mason’s Gain Rule, and Driving-Point Impedance Techniques Ronald G. Spencer, Member, IEEE Abstract—A pedagogical analysis of the modified MOS Wilson many students are enlightened as the subject matter is suddenly current mirror using signal flow graphs (SFGs), Mason’s gain reduced to something more rational. rule, and driving-point impedance (DPI) techniques is presented In [1], Sedra and Smith do a good job of making the con- as an exercise for undergraduate electrical engineering students nection between the amount of feedback and the corresponding learning to analyze transistor-level circuits with multiple-feed- back loops. While students often prefer the SFG representation decreases in gain and changes in input and output resistances. for single feedback loops, they often abandon it in favor of the In the chapter on feedback they lead the student into an implicit more familiar nodal analysis methods for multiple loops. Yet understanding of some tradeoffs; e.g., that a decrease in gain due these methods can be long and cumbersome and contribute little to feedback leads to a change in some other quantity by the same to intuition. In an attempt to preserve the intuitive grasp of amount. Fortunately, the students can verify the direct relation- tradeoffs, this paper presents an exercise of several well-estab- ship between these quantities using fundamental analytical tech- lishe