Studio_9

Studio_9 - 1 Studio 8 & 9 Review...

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Unformatted text preview: 1 Studio 8 & 9 Review Operational Amplifer Stability Compensation Miller EFFect Phase Margin Unity Gain requency Slew Rate Limiting Reading: Razavi ch. 9, 10 Lab 8, 9 op-amp is ig. 10.34 in sec. 10.5.1 (see also Johns & Martin sec 5.2 pp. 232-242) 2 Two-stage op-amp 3 Analysis Strategy Recognize sub-blocks Represent as cascade of simple stages 4 Total op-amp model Input differential pair Common source stage r O2 ||r O4 r O5 ||r O8 5 DC operating point I D [ ! A] V GS-V TH M1 25 0.235 M2 25 0.235 M3 25 0.247 M4 25 0.247 M5 50 0.350 M6 50 0.332 M7 50 0.332 M8 50 0.332 6 Small signal parameters I D [ A] V GS-V TH g m [ A/V] r O M1 25 0.235 208 M2 25 0.235 800k M3 25 0.247 M4 25 0.247 1.43M M5 50 0.350 285 715k M6 50 0.332 M7 50 0.332 M8 50 0.332 400k Note: n = 0.050 V-1 ; p = 0.028 V-1 7 Total op-amp model: Low frequency gain Input differential pair Common source stage a v 1 = g m 1 r O 2 r O 4 ( ) a v 1 = 208 A V ( ) 800 k " 1.43 M " ( ) a v 1 = 106 a v 2 = g m 2 r O 5 r O 8 ( ) a v 2 = 285 A V ( ) 400 k " 715 k " ( ) a v 2 = 73 r O2 ||r O4 r O5 ||r O8 8 Total op-amp model with capacitances Gate of M5 Load: scope probe 10pF C g = (900 m )(10 m ) 4.17 E ! 4 F m 2 " # $ % C g = 3.74 pF r O2 ||r O4 r O5 ||r O8 9 Total op-amp model with capacitances First stage pole Second stage pole f p 1 = 1 2 " r O 2 r O 4 ( ) C g 5 f p 1 = 1 2 " 800 k # 1.43 M # ( ) 3.74 pF ( ) f p 1 = 82 kHz f p 1 = 1 2 " r O 5 r O 8 ( ) C L f p 1 = 1 2 " 400 k # 715 k # ( ) 10 pF ( ) f p 1 = 61 kHz r O2 ||r O4 r O5 ||r O8 10 Open loop transfer function Product of individual stage transfer functions A ( j " ) = g m 1 r O 2 r O 4 ( ) 106 6 7 4 8 4 g m 5 r O 5 r O 8 ( ) 73 6 7 4 8 4 1 + j...
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This note was uploaded on 10/13/2009 for the course ECE 4902 taught by Professor Mcneill during the Spring '01 term at WPI.

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Studio_9 - 1 Studio 8 & 9 Review...

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