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Lecture10a

# Lecture10a - Lecture 10 DIGITAL OPERATION Topics Transistor...

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Lecture 10. DIGITAL OPERATION Objectives: Topics: Design circuits with transistor switches Design BJT logic inverters Describe operation of CMOS logic inverters Transistor as a Switch BJT logic Inverter CMOS Logic Inverter

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Digital Operation Voltage levels are used to represent binary signals v High Low ‘High’ and ‘Low’ levels depend on the type of logic used Undefined region - undesireable
Transistor as a Switch + V - Load control input + V - Load control input BJT Open Closed MOSFET Open Closed What works better when closed?

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EXAMPLE v IN =5V (LED ON), 0V (LED OFF) LED: V f1 =2V, i 1mA, P max =15mW BJT: V f =0.6V, V sat =0.2V, β F =50 R B , R C -? mA V P i f MAX MAX C 5 . 7 2 015 . 0 1 _ = = = 1mA i C 7.5mA Goal: v IN =0V – cutoff, v IN =5V – saturation V CC =i C R C +V f1 +V CE How large i B do we need to saturate the BJT? i B i C / β F f B B BE B B IN V i R V i R v + = + =
Digital Logic Inverter v IN v OUT v IN v OUT v IN v OUT

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BJT Logic Inverter V CC =5V, V f =0.6V, V sat =0.2V, β F =100 v IN = (0V-0.5V) – logic ‘0’; (3V-5V) – logic ‘1’

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Lecture10a - Lecture 10 DIGITAL OPERATION Topics Transistor...

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