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Learn the fundamentals of using op-amps in medical instrument circuit design and troubleshooting. Understand op-amp characteristics, practical applications, circuit gain, feedback, and troubleshooting techniques in a lab setting.
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Building Circuits 415-3
General medical device gain sensor filter v gain Further processing, display, etc. filter ADC 415-3
Breadboards 415-3
Breadboards 415-3
Breadboards 415-3
Breadboards 415-3
Breadboards 415-3
Breadboards 415-3
Op amps will be used in most labs. • d – differential • A – voltage gain • Z – impedance (usually resistive) 415-3
Ideal op amps • ZD →∞ Ω • Zout →0 Ω • AD →∞ V/V • Therefore, 415-3
We must use negative feedback to achieve non-saturated output. • The output is connected to the inverting input of the op amp. • The circuit gain, G, is much reduced from AD. • The voltages at the two inputs are nearly equal. • Use above and i+,-=0A to solve op amp circuits. • Voltage follower • Inverting amplifier 415-3
Answers? • Voltage follower • G=? • Inverting amplifier • G=? 415-3
Answers? • Voltage follower • G=1V/V • Inverting amplifier • G=-10k/680=-14.7V/V 415-3
In lab we don’t have ideal op amps. • Manufacturer’s produce spec sheets that detail actual device characteristics. • The first page has the device name, a general description, and call-outs of important features. 415-3
“Connection Diagrams” tell how to hook up the op amp. • NC – no connection • V+, V- are DC power connections • Dual-in-Line package (or DIP) fits in breadboard • Most op amps have similar pinouts, but there are differences! 415-3
Compare to a real chip Note: This is the positive power supply voltage, not the non-inverting input (which is labeled v+ in every textbook). 415-3
Op amps on your breadboard Negative power supply Ground Positive power supply 415-3
Op amps come have maximum ratings • Check max. supply and input voltages • Other Max ratings will probably not be important for this course. 415-3
Much of the info is in tables or charts • Each characteristic may be described by a minimum, typical, or maximum value • The numbers apply only under conditions listed. • Check Units! • There are more characteristics listed than we will learn about. 415-3
Troubleshooting in lab • Know what to expect • Given input, what should output be? • Given resistor tolerances and op amp specs, is output reasonable? • Check the power supplies • Are they on? • Do the voltages indicated on the DC power supply actually appear at the op amp’s pins? • Overload lights? • Is the op amp operating in its linear region? • Is the output saturating? • Is the Gain-bandwidth product limiting the output? 415-3