Operational Amplifiers David Lomax Azeem Meruani Gautam Jadhav

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.

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

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

IC Circuit

What do they really look like?

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-

Inverting Amplifier R RFRF V in i in i out C

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

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:

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

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

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

Filters Low Pass Filters High Pass Filters Band Pass Filters

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

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

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

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

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

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

Real Vs Ideal Op Amp ParametersIdealTypical Input Impedance ∞10 6 Ω Output Impedance 0Ω0Ω Ω Voltage Gain∞ Common Mode voltage

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

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.

Open and Closed Loop Response

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

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

References David G Alciatore & Michael B. Histand, Introduction to Mechatronics and Measurement Systems Electronics book

Questions ?