Presentation on theme: "ME 6405 Operational Amplifiers 10/2/12"— Presentation transcript:
1 ME 6405 Operational Amplifiers 10/2/12 Alex Ribner Eric Sanford Christina Biggs
2 Outline by: Alex Ribner What is an Op Amp?Ideal versus Real CharacteristicsTypes of Op AmpsApplications
3 BackgroundOperational amplifiers (op-amps), use an external power source to apply a gain to an input signal.Made of resistors, transistors, diodes and capacitors.Variety of functions such as: mathematical operations, perform buffering or amplify AC and DC signals.
4 741 Op-Amp Schematic current mirror current mirror voltage level shifteroutput stagedifferential amplifiercurrent mirrorhigh-gain amplifier
5 Timeline 1946 –patent for an op-amp using vacuum tubes. 1953 –op-amps for sale1961 – discrete IC op-amp1965 – successful monolithic op-amps1968 – uA741
6 General Schematic Active device! Requires power. V+ - non-inverting inputV- - inverting inputVout – outputVs+ - positive power supplyVs- - negative power supplyVout=K(V+ - V-)Some Op Amps have more than these 5 terminals
7 FeedbackClosed loop configurations reduce the gain of the amplifier, but adds stability.Part of the output signal is applied back to the inverting input of the amplifier.Op amps use negative feedback.Negative feedback helps to: overcome distortion and non-linearity, tailor frequency response, and stabilize circuit properties from outside influences such as temperature.Although a closed loop configuration reduces the gain of the amplifier, it adds stability. In closed loop configuration, part of the output signal is applied back into the inverting input of the amplifier. This creates negative feedback, which is generally the type of feedback used with op amps. Positive feedback is mainly used in oscillators.t helps to overcome distortion and non-linearity.It allows the user to "tailor" frequency response to the desired values.It makes circuit properties predictable and less dependent on elements such as temperature or the internal properties of the device.Circuit properties are dependent upon the external feedback network and are thus easily controlled by external circuit elements.The System designer can concentrate on function and not the details of operating point selection, biasing, and the internal characteristics of discrete transistor amplifier design.
8 Behavior of an Op Amp Achieves: In Three Steps: Very high input impedanceVery high open loop gainVery low output impedance.In Three Steps:Differential input stage, draws negligible amounts of input current enables assumption for ideal Op Amp properties.Voltage gain stage, responsible for gaining up input signal and sending it to output stage.Output stage, delivers current to op amp’s load.The first stage is the differential input stage. It must have very high input impedance. This causes the op amp to draw very negligible amounts of input current. The very small input current enables the user to utilize the ideal op amp equations for circuit analysis purposes. In some designs this stage also provides the DC gain of the amplifier.The next stage is the voltage gain stage. This stage is mainly responsible for gaining up the input signal and sending it to the output stage.The output stage of the op amp delivers current to the op amp's load. It must have very low output impedance so that the loading of the output is minimized. This final stage may or may not have short circuit protection.
9 ‘Golden Rules’ of Ideal Op-Amps by: Eric Sanford These characteristics can be summarized with two ‘golden rules’:1 - The output attempts to do whatever is necessary to make the voltage difference between the inputs equal to zero (when used in a closed-loop design).2 - The inputs draw no current.
14 Basic Op-Amp Types by: Christina Biggs InvertingNon-InvertingIntegratingDifferentialSumming
15 Three Op Amp Setups Differential Input 2) Inverting Mode 3) Non-inverting ModeWhere should this go?
16 Non-Inverting Amplifier Analysis Amplifies the input voltage by a constantDetermined by voltage output
17 Derivation of Non-inverting Amplifier Vout=K(V+-V-)R1/(R1+R2) Voltage Divider RuleV-=Vout (R1/(R1+R2) )Vout=[Vin-Vout (R1/(R1+R2))] KVout=Vin/[(1/K)+ (R1/(R1+R2))]Use Voltage Divider Rule!!As discussed previously assuming, K is very large, we have:Vout=Vin/(R1/(R1+R2))Vout=Vin (1+(R2/R1))
18 Inverting Amplifier Amplifies and inverts the input voltage Polarity of the output voltage is opposite to the input voltageDetermined by both voltage input and outputvirtual ground
19 Derivation of Inverting Amplifier Vout=K(V+-V-)V-=Vout(Rin/(Rin+Rf))+Vin(Rf/(Rin+Rf))V-=(VoutRin+VinRf)/(Rin+Rf)Vout=K(0-V-)Vout=-VinRf/[(Rin+Rf)/K+(Rin)]Use Voltage Divider Rule!!K = gainVout=-VinRf/Rin
20 Op-Amp Integrator Integrates the inverted input signal over time Magnitude of the output is determined by length of time voltage is present at inputThe longer the input voltage is present, the greater the output
21 Op-Amp Differentiator Magnitude of output determined by the rate at which the applied voltage changes.Faster change, greater output voltageThe resistor and capacitor create an RC network
22 Op-Amp Summing Amplifier Scales the sum of the input voltages by the feedback resistance and input to produce an output voltage.
23 Op-Amp Differential Amplifier Produces an output proportional to the difference of the input voltagesIf R1 = R2 and Rf = Rg:
25 PID Controllers Goal is to have VSET = VOUT Set point = Input; P = Non-inverting, (dependent on gain); I =integrator; D=differentiator3 different Op-Amps in one setup!!!Inverter after each one negative gain.Goal is to have VSET = VOUTRemember that VERROR = VSET – VSENSOROutput Process uses VERROR from the PID controller to adjust Vout such that it is ~VSET
26 Strain GagesUse a Wheatstone bridge to determine the strain of an element by measuring the change in resistance of a strain gauge(No strain) Balanced BridgeR #1 = R #2(Strain) Unbalanced BridgeR #1 ≠ R #2
27 2nd Order Op-Amp Filters Three 2nd order filters: low pass, high pass, and bandpass.
29 References "What Is an Op Amp?" What Is an Op Amp? National, n.d. Web. 25 Sept < Student Lecture Fall Op-Amps… and why they are useful to us. Student Lecture Fall What is an Op-Amp? "Operational Amplifier." Wikipedia. Wikimedia Foundation, n.d. Web. 25 Sept < "Op-Amp Basics." Op-Amp Basics. N.p., n.d. Web. 27 Sept < Jung, Walter G. Op Amp Applications Handbook. Burlington, MA: Newnes, Web. 26 Sept < 05/op_amp_applications_handbook.html>. "Operational Amplifiers." Operational Amplifiers. N.p., n.d. Web. 25 Sept <