ME 6405 Introduction to Mechatronics Operational Amplifiers Chris Nygren Matt Livianu Brad Schwagler

ME 6405 Introduction to Mechatronics Agenda Introduction Background Amplifier Introduction Basic Circuits Review Characteristics of an Ideal Op Amp Types of Op Amps Practical Applications Conclusion Quiz

ME 6405 Introduction to Mechatronics Purpose To introduce the Operational Amplifier by providing background, functionality, applications, and relevance to Mechatronics class projects.

ME 6405 Introduction to Mechatronics Introduction Operational Amplifiers are represented both schematically and realistically below: –Active component!

ME 6405 Introduction to Mechatronics Background Originally invented in early 1940s using vacuum tube technology –Initial purpose was to execute math operations in analog electronic calculating machines Shrunk in size with invention of transistor Most now made on integrated circuit (IC) –Only most demanding applications use discrete components Huge variety of applications, low cost, and ease of mass production make them extremely popular

ME 6405 Introduction to Mechatronics Amplifiers Differential Amplifier –Amplifies difference between inputs Single-ended Amplifier

ME 6405 Introduction to Mechatronics Operational Amplifier Output gain high –A ~= 10 6 Tiny difference in the input voltages result in a very large output voltage –Output limited by supply voltages Comparator –If V + >V -, V out = HVS –If V + <V -, V out = LVS –If V + =V -, V out = 0V

ME 6405 Introduction to Mechatronics 3-stage Op-Amp

ME 6405 Introduction to Mechatronics Sensor signals are often too weak or too noisy –Op Amps ideally increase the signal amplitude without affecting its other properties Why are they useful?

ME 6405 Introduction to Mechatronics Negative feedback leads to stable equilibrium Voltage follower (direct feedback) –If Vout = V-, then Vout ~ V+ Closed Loop Transfer Function H(s) = A / (1 + AF) When AF >> 1… H(s) = 1 / F Why are they useful? Where: A = Op Amp Open Loop Gain F = Feedback Loop Gain

ME 6405 Introduction to Mechatronics 1.The output attempts to do whatever is necessary to make the voltage difference between the inputs zero. 2.The inputs draw no current.

ME 6405 Introduction to Mechatronics Basic Circuits Review Kirchoff’s Law –Voltage Law: The sum of all the voltage drops around the loop = V in Resistance (Ohms – Ω) –Series –Parallel V 1 + V 2 + V 3 = V in

ME 6405 Introduction to Mechatronics Basic Circuits Review Capacitance (Farad – F) –Series –Parallel Inductance (Henry – H) –Series –Parallel

ME 6405 Introduction to Mechatronics Ideal Op Amp Z in is infinite Z out is zero Amplification (Gain) V out / V in = ∞ Unlimited bandwidth V out = 0 when Voltage inputs = 0

ME 6405 Introduction to Mechatronics Ideal Op Amp Ideal Op-AmpTypical Op-Amp Input Resistanceinfinity 10 6  (bipolar) 10 9   (FET) Input Current – A Output Resistance0 100 – 1000  Operational Gaininfinity Common Mode Gain BandwidthinfinityAttenuates and phases at high frequencies (depends on slew rate) TemperatureindependentBandwidth and gain

ME 6405 Introduction to Mechatronics How are Op-Amps used? Comparator (seen earlier) Voltage follower (seen earlier) Signal Modulation Mathematical Operations Filters Voltage-Current signal conversion

ME 6405 Introduction to Mechatronics Non-inverting Op-Amp Uses: Amplify…straight up

ME 6405 Introduction to Mechatronics Inverting Op-Amp Uses: Analog inverter

ME 6405 Introduction to Mechatronics Comparator Uses: Low-voltage alarms, night light controller V2V2 V1V1 V out

ME 6405 Introduction to Mechatronics Pulse Width Modulator Output changes when –V in ~= V pot Potentiometer used to vary duty cycle Uses: Motor controllers

ME 6405 Introduction to Mechatronics Summation Uses: Add multiple sensors inputs until a threshold is reached.

ME 6405 Introduction to Mechatronics Difference If all resistors are equal:

ME 6405 Introduction to Mechatronics Integrating Op-Amp Uses: PID Controller

ME 6405 Introduction to Mechatronics Differentiating Op-Amp (where V in and V out are functions of time)

ME 6405 Introduction to Mechatronics Filters Decouple the low-pass RC filter from the load. Uses: Simple audio. Remove frequencies over 20kHz (audible)

ME 6405 Introduction to Mechatronics Low-pass Filter (active) Cutoff frequency This works because the capacitor needs time to charge.

ME 6405 Introduction to Mechatronics High pass filter (active) Band-pass filter cascades both high-pass and low-pass!

ME 6405 Introduction to Mechatronics Measuring current Current (I) better than voltage (V) for measurement –Voltage suffers losses due to resistances in path –Low impedance is better for resisting noise So how do we generate a constant current source? –Transconductance Amplifier

ME 6405 Introduction to Mechatronics Transconductance Amp Precision 250Ω resistor 1V / 250 Ω = 4mA 5V / 250 Ω = 20mA R Load doesn’t matter, just as long as op-amp has high enough voltage rails Uses: - In: Sensors (temp, pressure, etc), - Out : Radios (Variable Freq Osc)

ME 6405 Introduction to Mechatronics Conclusions Op-Amps are often used for –Sensor amplification –Mathematical operations (sums, difference, inverse) –Filters (High/Low/Band pass) –Measurement devices Current in –> Voltage out

ME 6405 Introduction to Mechatronics Questions? Does an Op-Amp amplify current or voltage? Can you use an Op-Amp as a buffer? If so, How? Why should you care about the device bandwidth rating? What is the most common Op Amp chip? What is an ‘active’ component? Is an Op Amp an active or a passive component? What is the advantage of an active vs. passive filter?

ME 6405 Introduction to Mechatronics Practical Tips Try to use single supply op-amps in order to minimize need for a 10V difference from power supply Good low resistance, twisted, and shielded wire should be used when a sensor is located far away from the op-amp circuit. Minimize current draw in sensor circuits to reduce thermal drift Filter power into op-amp circuits using capacitors Design op-amp circuits so output cannot be negative in order to protect 68HC11 A/D port. Isolate op-amp circuit output with unity gain op-amp if connected to an actuator. Make sure bandwidth of op-amp is adequate Use trimmer potentiometers to balance resistors in differential op-amp circuits Samples of op-amps can be obtained from National Semiconductor (

ME 6405 Introduction to Mechatronics Bibliography “Mechatronics”, Sabri Cetinkunt Wikipedia.org Allaboutelectronics.com