77 Op Amps - Making Sens e of EE 2nd edition Op Am p...

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Making Sense of EE // 2nd edition Op Amp circuits © 2008 A. Ganago © 2008 A. Ganago Op Amp Circuits 1 Circuits With Operational Amplifiers (Op Amps) Op Amps are among workhorses of today’s electronics You will strongly benefit yourself by learning how to use them © 2008 A. Ganago Op Amp Circuits 2 Op Amp’s Terminals Inverting Input Non-Inverting Input Output Power supply’s Positive voltage +V CC Power supply’s Negative voltage -V CC (or the ground) © 2008 A. Ganago Op Amp Circuits 3 In all circuits, V OUT is limited by the power supply’s voltages " V CC # V OUT # + V CC V + V - +V CC -V CC V OUT © 2008 A. Ganago Op Amp Circuits 4 I - = 0 I + = 0 “Golden Rule” #1: Op Amp’s input currents = zero This is a good approximation in ALL Op Amp circuits © 2008 A. Ganago Op Amp Circuits 5 Feedback is a connection between the output terminal and one of the input terminals: • NEGATIVE feedback • POSITIVE feedback © 2008 A. Ganago Op Amp Circuits 6 “Golden Rule” #2: Op Amp’s input Voltages equal each other: V+ = V- V + V - V OUT This is true ONLY in circuits with NEGATIVE feedback Page 1 of 7
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Making Sense of EE // 2nd edition Op Amp circuits © 2008 A. Ganago © 2008 A. Ganago Op Amp Circuits 7 Op Amp’s OUTPUT Voltage V OUT = (V+ - V-) A, where A is huge ~10 6 or more V + V - V OUT In circuits with POSITIVE feedback © 2008 A. Ganago Op Amp Circuits 8 Op Amp’s OUTPUT Voltage V OUT = (V+ - V-) A, where A is huge ~10 6 or more V + V - V OUT In circuits without any feedback © 2008 A. Ganago Op Amp Circuits 9 Formally, for (V+ - V-) = 1 mV V OUT = (V+ - V-) A ~ 1 kV Because A is huge ~10 6 or more V + V - V OUT In circuits without any feedback © 2008 A. Ganago Op Amp Circuits 10 Recall that V OUT is limited V OUT " V CC # V OUT # + V CC V + V - +V CC -V CC Thus, for (V+ - V-) = +1 mV V OUT +V CC © 2008 A. Ganago Op Amp Circuits 11 Recall that V OUT is limited V OUT " V CC # V OUT # + V CC V + V - +V CC -V CC Thus, for (V+ - V-) = -1 mV V OUT -V CC © 2008 A. Ganago Op Amp Circuits 12 Recall that V OUT is limited V OUT " V CC # V OUT # + V CC V + V - +V CC Thus, for (V+ - V-) = -1 mV V OUT 0 if -V CC = zero (ground) Page 2 of 7
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Making Sense of EE // 2nd edition Op Amp circuits © 2008 A. Ganago © 2008 A. Ganago Op Amp Circuits 13 V + V - V OUT
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