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Operational Amplifiers David Lomax Azeem Meruani Gautam Jadhav

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What is an Op-Amp Low cost integrating circuit consisting of: Transistors Resistors Capacitors Able to amplify a signal due to an external power supply Name derives from its use to perform operations on a signal.

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Applications of Op-Amps Simple Amplifiers Summers Comparators Integrators Differentiators Active Filters Analog to Digital Converters

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Symbol for an Op-Amp +V -V Inverting Input Terminal Non-Inverting Input Terminal

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IC Circuit

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What do they really look like?

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Ideal Op-Amps Infinite input impedance I + = I - = 0 Infinite gain V + = V - Zero output impedance Output voltage is independent of output current Vout V+V+ V-V- I+I+ I-I-

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Inverting Amplifier R RFRF V in i in i out C

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Non-Inverting Amplifier R RFRF i in i out C V in

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Summing Circuits Used to add analog signals Voltage averaging function into summing function Calculate closed loop gain for each input If all resistors are equal in value:

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Difference Circuit Used to subtract analog signals Output signal is proportional to difference between two inputs If all resistors are equal:

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Integrating Circuit Replace feedback resistor of inverting op-amp with capacitor A constant input signal generates a certain rate of change in output voltage Smoothes signals over time

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Differentiating Circuit Input resistor of inverting op-amp is replaced with a capacitor Signal processing method which accentuates noise over time Output signal is scaled derivative of input signal

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Filters Low Pass Filters High Pass Filters Band Pass Filters

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Low Pass Filter Used to filter out signals above a specified frequency Example: Noise Frequency range is governed by: Where R = R 2 C = C 2

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High Pass Filter Filters out frequencies below a specified frequency Reverse locations of resistors and capacitors in a low pass filter

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Band Pass Filter Created by combining a high and low pass filter Only allows signals within frequency ranges specified by the low and high pass filters to pass

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Comparator Circuit Determines if one signal is bigger than another No negative feedback, infinite gain and circuit saturates Saturation: output is most positive or most negative value V 1 is V ref V 2 is V in

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OR Gate If U 1 or/and U 2 = 5V, U 3 = 5V If U 2 and U 1 = 0V, U 3 = 0V

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Offset Comparator If U 3 = 0V If U 3 = 5V

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Real Vs Ideal Op Amp ParametersIdealTypical Input Impedance ∞10 6 Ω Output Impedance 0Ω0Ω100-1000Ω Voltage Gain∞10 5 - 10 9 Common Mode voltage 010 -5

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Non-Ideal Op-Amps Gain Bandwidth Falloff Frequency Slew Rate ( ΔV / ΔT ) Rise Time

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Gain Bandwidth Gain Bandwidth Product (GBP)- is the product of the open-loop gain and the bandwidth at that gain. For practical purposes the actual gain should only be 1/10 to 1/20 of the open loop gain at a given frequency to ensure that the op-amp will operate without distortion.

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Open and Closed Loop Response

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Important Parameters for Op-Amps Input Parameters Voltage (Vicm) Offset voltage Bias current Input Impedance Output Parameters Short circuit current Voltage Swing Open Loop Gain Slew Rate

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Where to buy Op-Amps Newark Electronics Radio Shack DigiKey Jameco

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References David G Alciatore & Michael B. Histand, Introduction to Mechatronics and Measurement Systems http://www.elexp.com/t_gain.htm http://allaboutelectronics.com Electronics book

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Questions ?

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