EE 330 Lect 35 Spring 2011

EE 330 Lect 35 Spring 2011 - EE 330 Lecture 35 Current...

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EE 330 Lecture 35 Current Source Biasing Current Sources and Mirrors
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B E C V DD V in R C V out R E V EE B E C V SS V DD V in R E V out B E C V DD V in R C V out V EE A V C E R - R R in R out πE r+ βR C R C R mC gR -1 m g B E C V BB V DD V in R C V out m mE g g +g r+βR -g R π r C R t E CQ V βR I    CQ C t IR V DQ C EB 2I R V DQ EB 2I V CQ t I V CQ E CQ E t I R +V DQ E DQ E EB 2I R 2I R +V t E CQ V I t CQ βV I DQ C EB 2I R V CQ C t V -1 m g DQ EB 2I V CQ t I V MOS BJT MOS MOS MOS BJT BJT BJT CE/CS CC/CD CB/CG CEwRE/CSwRS Basic Amplifier Gain Table Can use these equations only when circuit is EXACTLY like that shown above !! Review from Last Lecture
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B E C V DD V in R C V out R E V EE B E C V SS V DD V in R E V out B E C V DD V in R C V out V EE B E C V BB V DD V in R C V out CE/CS CC/CD CB/CG CEwRE/ CSwRS Basic Amplifier Characteristics Summary Reasonably accurate but somewhat small gain (resistor ratio) High input impedance Moderate output impedance Used when more accurate gain is required Large noninverting gain Low input impedance Moderate (or high) output impedance Used more as current amplifier or, in conjunction with CD/CS to form two-stage cascode Large noninverting gain Low input impedance Moderate (or high) output impedance Used more as current amplifier or, in conjunction with CD/CS to form two-stage cascode Gain very close to +1 (little less) High input impedance for BJT (high for MOS) Low output impedance Widely used as a buffer Review from Last Lecture
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High-gain BJT amplifier m V m C 0C -g A -g R gG B E C V DD V in R C V out V EE To make the gain large, it appears that all one needs to do is make R C large ! CQ C V m C t -I R A -g R V But V t is fixed at approx 25mV and for good signal swing, I CQ R C <(V DD- V EE )/2 DD EE V t VV A 2V If V DD -V EE =5V, 100 V 5V A 2 25mV  Gain is practically limited with this supply voltage to around 100 Review from Last Lecture
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High-gain MOS amplifier m V m D 0D -g A -g R gG G S D V DD V in R D V out V SS To make the gain large, it appears that all one needs to do is make R D large ! DQ D V m D EB -2I R A -g R V But V EB is practically limited to around 100mV and for good signal swing, I DQ R D <(V DD- V SS )/2 DD SS V EB VV A V If V DD -V SS =5V and V EB =100mV, 50 V 5V A 100mV  Gain is practically limited with this supply voltage to around 100 Are these fundamental limits on the gain of the BJT and MOS Amplifiers?
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EE 330 Lect 35 Spring 2011 - EE 330 Lecture 35 Current...

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