6.8 Lecture23 Cascode with Active Load and Cascode Configurations_1

# 6.8 Lecture23 Cascode with Active Load and Cascode Configurations_1

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EE 311 Lecture 23 Wed. March 3, 2010 6.8 Cascode Amplifier With Active Load Zubair Rehman

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2 Advisement Circus 10 AM Dr. Liu EE 413 10:40 AM Dr. Anderson EE 455
3 Q1 is CS R in1 = infinity R out1 = r 01 Q2 is CG R in2 = [(r 02 + R L )] / [1 + (g m +g mb )r o ] = [1 / (g m2 +g mb2 )] + (R L / A v02 ) Where A v02 = [1 + (g m +g mb )r o ] R out2 = r 02 * [(g m +g mb )R S2 + 1] + R S2 where R S2 = r O1 R out2 = r 02 * [(g m +g mb )r 01 + 1] + r 01 ~ (g m +g mb )r O2 r O1 +r 01 = A v02 r 01 +r 01 Figure 6.36 (a) The MOS cascode amplifier. (b) The circuit prepared for small-signal analysis with various input and output resistances indicated. (c) The cascode with the output open-circuited.

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4 Open-Circuit Voltage Gain (R L = infinity) R in1 = infinity v i = v sig i i = g m1 v gs1 = g m1 v i R in2 = infinity v d1 = v s2 = - i 1 r 01 = - g m1 r 01 v i v gs2 = v g2 - v s2 = 0 - (- g m1 r 01 v i ) = + g m1 r 01 v i i 2 = (g m2 +g mb2 )v gs2 = + (g m2 +g mb2 )*( g m1 r 01 v i ) v ds2 = -i 2 r 02 = - [(g m2 +g mb2 ) * (g m1 r 01 * v i )] r 02 v o = v ds2 + v ds1 = v ds2 + v d1 v o = - [(g mb

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Unformatted text preview: + g mb2 )r 02 * g m1 r 01 + g m1 r 01 ]v i A vo = v o / v i = A vo2 A vo1 + A vo1 = A vo2 A vo1 A vo ~ A vo2 A vo1 R out ~ A vo2 r o1 Voltage Model For Cascade + R in =Infinity 5 Transconductance Model To Determine G m , Short Output i SC = G m v i = A vo v i / R out = A vo2 A vo1 v i / A vo2 r o1 G m = A vo1 / r o1 = g m1 r o1 / r o1 = g m1 R in =Infinity R out 6 Cascode Mirror vs. Simple Mirror 7 Double Cascoding Change R s1 to R s2 8 The Folded Cascode (Avoids The Stacking Problem) Very popular building block in CMOS 9 The BJT Cascode R OUT = (g m2 r 02 )”R e2 ” but “R e2 ” = r 01 || r π2 R OUT = g m2 r 02 * (r 01 || r π2 ) ≈ g m2 r 02 r π2 = g m2 r π2 r 02 R OUT = β 2 r 02 10 Bi CMOS Cascodes...
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6.8 Lecture23 Cascode with Active Load and Cascode Configurations_1

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