03ECE108Ch3Twoterminapullupinverters

03ECE108Ch3Twoterminapullupinverters - 3. Two-Terminal Pull...

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3. Two-Terminal Pull up MOSFET Inverters: General Characteristics ECE 108 1 Esener ECE108
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3. 1. Inverter Currents and Voltages 2 Esener ECE108 S V DD LOAD or PULL-UP D V G + V in = V GS DRIVER or PULL-DOWN V 0 = V DS + V L =V DD -V O I D Device Equations I L = f L (V L ) I D = f D (V GS ; V DS ; V T ) Circuit Equations V L =V DD -V O I D = I L f L (V DD -V O ) = f D (V IN ; V O ; V ) V IN =V GS V O =V DS => Transfer characteristics S V DD K L D V G + V in = V GS V 0 = V DS + I L =K L (V DD -V O ) I L
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3.2. INVERTER THRESHOLD VOLTAGE Esener ECE108 3 ( 29 ( 29 ( 29 ( 29 ] 1 V V 2 1 [ B 1 V V 0 V V B 2 V V B 2 V V T DD inv inv inv 2 inv T T T T - - + + = = - - - + - B The inverter logic threshold voltage is the input voltage that results in an equal output voltage ( V inv =V GS = V DS = V O ) (Text book uses V M for V inv ) Using the constraint, V inv =V GS = V DS ( 29 ( 29 2 inv L D inv DD inv DS 2 inv D DS DD L T T V V 2K k V V V V V V 2 k ) V (V K - = - = - = - V IN > V inv Output Low V IN < V Output High [] V B Note B K k Let 1 - L D = =
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3.3. COMPUTING V OH & V OL Esener ECE108 4 0 I I L D = = Neglecting the leakage current in the pull down MOSFET (off) I L =K L (V DD -V O ) } => => V OH = V DD V IN =V GS =0 => V GS < V T => Pull down off I D = 0 V OH for V IN =0 V OL for V IN = V DD ( 29 ( 29 T DD DD OL 2 OL DD OL T DD 2 OL 2 OL OL DD D OL DD L V V B 1 V V small very is V since and 0 B 2V V V V B 1 2 V 2 V V V V k ) V (V K T - + = = + - + -
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03ECE108Ch3Twoterminapullupinverters - 3. Two-Terminal Pull...

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