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Announcements

Announcements. Tuesday ’ s Lecture next week is cancelled October 18 th Assignment 4 is active, due in my mailbox by 5pm Friday (October 14 th ) Mid-term Thursday, October 27 th. Project Dates.

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Announcements

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  1. Announcements • Tuesday’s Lecture next week is cancelled • October 18th • Assignment 4 is active, due in my mailbox by 5pm Friday (October 14th) • Mid-term Thursday, October 27th

  2. Project Dates • Project Description - one paragraph, plus circuit diagrams and web links – email to me by Tuesday Nov 1st • Guidelines and a few useful links are here: http://www.physics.udel.edu/~jholder/Phys645/Lab/Projects.htm . There are many more sites if you search the web (e.g. google “hobby electronics”) • Kits are allowed, but circuits must be assembled on the prototyping board. $50 maximum budget. • Once approved, I will need a complete parts list, with digikey or radioshack catalog part numbers. I will place the orders, but FINDING THE CORRECT COMPONENTS AND GETTING THEM IN TIME IS YOUR RESPONSIBILITY!!! Note that most basic components (resistors, capacitors etc.) are available in the lab. • The project should (ideally) contain both analog and digital • You should work with your lab partner, but individual reports are required for the projects. • The project counts for 20% of your final grade (I grade them) • I will leave copies of some good past projects in the lab (please don’t take them away)

  3. Lecture 12 Overview • Op amp circuits • amplifiers • Adding/ Subtracting • Integrating Circuit • Differentiating Circuit • Active Filters

  4. Recap: Opamps • DC coupled, very high gain, differential amplifier. • Feed part of the output back into the inverting input to get stable operation in the linear amplification region • Golden rules under negative feedback: • The voltage at the inputs is the same (v+=v-) • No current flows into the opamp (i+=i-=0)

  5. Op amp circuit 2: Inverting Amplifier • Signal and feedback resistor, connected to inverting (-) input. • v+=v- connected to ground v+ grounded, so:

  6. Op amp circuit 3: Summing Amplifier • Same as previous, but add more voltage sources

  7. Summing Amplifier Applications • Adds signals from a number of waveforms • Applications - audio mixer • http://wiredworld.tripod.com/tronics/mixer.html • Can use unequal resistors to get a weighted sum • For example - could make a 4 bit binary - decimal converter • 4 inputs, each of which is +1V or zero • Using input resistors of 10k (ones), 5k (twos), 2.5k (fours) and 1.25k (eights)

  8. Op amp circuit 4: A non-inverting amplifier • Feedback resistor still to inverting input, but no voltage source on inverting input (note change of current flow) • Input voltage to non-inverting input

  9. Op amp circuit 5: Differential Amplifier (subtractor) • Useful terms: • if both inputs change together, this is a common-mode input change • if they change independently, this is a normal-mode change • A good differential amp has a high common-mode rejection ratio (CMMR)

  10. Differential Amplifier applications • Very useful if you have two inputs corrupted with the same noise • Subtract one from the other to remove noise, remainder is signal • Many Applications : e.g. an electrocardiagram measures the potential difference between two points on the body http://www.picotech.com/applications/ecg.html The AD624AD is an instrumentation amplifier - this is a high gain, dc coupled differential amplifier with a high input impedance and high CMRR (the chip actually contains a few opamps)

  11. Op-amp integrator

  12. Op-amp integrator

  13. Integrator Application: Ramp Generator V Integrator response to a constant voltage: VIN This is a ramp generator - very useful in timing circuits... t VOUT V • What's the integrator response to a square wave?

  14. Integrator Application: Ramp Generator V Integrator response to a constant voltage: VIN This is a ramp generator - very useful in timing circuits... t VOUT V • What's the integrator response to a square wave? VIN t • ...Useful for waveform generators: VOUT

  15. What does this do?

  16. Op-amp differentiator

  17. Differentiator • Differentiator response to a square wave?:

  18. Differentiator Application: edge detection VIN • Differentiator response to a square wave?: • The differentiator is good at detecting edges, or transitions - very useful in digital circuits. t VOUT N.B. Don't confuse the differentiator with a differential amplifier (subtractor)!

  19. Other "mathematical operator" circuits can be easily constructed: • Logarithm • Antilogarithm • Multiplier • Divider • Square root function

  20. What about complex impedances?

  21. Active low-pass filter Max Amplification: RF/RS Low pass factor: 1/(1+ jωRFCF) Cut-off frequency (-3dB = 1/√2) when ωRFCF=1, ie ω0=1/RFCF e.g. RF/RS=10; 1/RFCF=1

  22. Active high-pass filter Max Amplification: RF/RS High pass factor: 1/(1+ 1/jωRSCS) Cut-off frequency: ωRFCF=1 e.g. RF/RS=10; 1/RFCF=1

  23. Active band-pass filter Combine the two: • Advantages of active filters: • no inductors (large, pick-up) • buffered (high input impedance, low output impedance) • – so filter performance independent of source and load; can cascade filters

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