OpAmp-tutorial-1

To the operational amplifier vs inverting i vid

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Unformatted text preview: iscrete devices. to The Operational Amplifier +VS Inverting _ i(-) vid Noninverting i(+) RO Ri Output vO = Advid A + -VS • i(+), i(-) : Currents into the amplifier on the inverting and noninverting lines respectively respectively • vid : The input voltage from inverting to non-inverting inputs • +VS , -VS : DC source voltages, usually +15V and –15V • Ri : The input resistance, ideally infinity • A : The gain of the amplifier. Ideally very high, in the 1x1010 range. • RO: The output resistance, ideally zero • vO: The output voltage; vO = AOLvid where AOL is the open-loop voltage gain The Four Amplifier Types The Description Gain Symbol Transfer Function Voltage Amplifier or Voltage Controlled Voltage Source (VCVS) Av vo/vin Current Amplifier or Current Controlled Current Source (ICIS) Ai io/iin Transconductance Amplifier or Voltage Controlled Current Source (VCIS) gm (siemens) io/vin Transresistance Amplifier or Current Controlled Voltage Source (ICVS) rm (ohms) vo/iin VCVS (Voltage Amplifier) Summary VCVS Noninverting Configuration i(+) + vid vin + _ iO _ i(-) + vF _ + Applying KVL the Applying following equations can be found: can v1 = vin vO = v1 + vF = vin+ iFRF v1 _ vid = vo/AOL iL + iF RF RL R1 i1 + vL _ Assuming AOL vO - vid =0 Also, with the Also, assumption that Rin = assumption i(+) = i(-) = 0 This means that, This i F = i1 Therefore: iF = vin/R1 Using the equation to the left the output Using voltage becomes: voltage vo = vin + vinRF = vin RF + 1 R1 R1 VCVS (Voltage Amplifier) Summary VCVS Noninverting Configuration Continued The closed-loop voltage gain is symbolized by A v and is found to be: A v = v o = RF + 1 vin R1 The original closed loop gain equation is: AF is the amplifier Av = AF = AOL 1 + AOL gain with feedback feedback Ideally AOL , Therefore Av = 1 Ideally Note: The actual value of AOL is given for the specific device and Note: usually ranges from 50k 500k. is the feedback factor and by assuming open-loop gain is infinite: is = R1 R1 + RF VCVS (Voltage Amplifier) Summary VCVS Noninverting Configuration Continued Input and Output Resistance Ideally, the input resistance for this configuration is infinity, but the a Ideally, closer prediction of the actual input resistance can be found with the following formula: following RinF = Rin (1 + AOL) Where Rin is given for the specified device. Usually Rin is specified...
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This document was uploaded on 03/31/2014.

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