MFETMirrSu10 - c Copyright 2008. W. Marshall Leach, Jr.,...

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° Copyright 2008. W. Marshall Leach, Jr., Professor, Georgia Institute of Technology, School of Electrical and Computer Engineering. FET Current-Mirror Examples Common-Source Ampli f er Figure 1 shows a common-source ampli f er. The active device is M 1 . Its load consists of a current- mirror active load consisting of M 2 and M 3 .Thecu r ren tsou rce I REF sets the drain current in M 3 which is mirrored into the drain of M 2 . Because the source-to-drain voltage of M 2 is larger than that of M 3 ,theEar lye f ect causes the dc drain current in M 2 to be slightly larger than I REF . Figure 1: Common-source ampli f er. The voltage V G is the dc component of the gate input to M 1 . It is a dc bias voltage which sets the dc drain current in M 1 . This current must be equal to the drain current in M 2 in order for the dc output voltage to be stable. In applications, V G would usually be set by feedback. It will be assumed that r 01 = in calculating i o ( sc ) but not in calculating r out . Note that the body e f ect must be accounted for in M 1 . Assume that I D 1 = I D 2 = I D 3 = I REF . (a)Usethesourceequ iva lentc ircu ittoca lcu late the short-circuit output current. Assume that r 01 = . i o ( sc ) = i 0 d 1 = i 0 s 1 = v i (1 + χ 1 ) r is 1 + R S r is 1 = r s 1 1+ χ 1 = 1 g m 1 (1 + χ 1 ) where g m 1 =2 p
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This note was uploaded on 05/26/2011 for the course ECE 3050 taught by Professor Hollis during the Summer '08 term at Georgia Institute of Technology.

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MFETMirrSu10 - c Copyright 2008. W. Marshall Leach, Jr.,...

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