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Analog Electronics Workshop Input/Output Limitations

Analog Electronics Workshop Input/Output Limitations. Rev 0.2 March 13, 2013. What’s Wrong?. Common Mode Voltage Definition. Input and Output Swing. Vcm Range. Output Swing. Vcm. Vout. Vcm – Two Examples. Vcm = 0V. Vcm = 5V. Input Stage. Output Stage. V SAT. V BE.

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Analog Electronics Workshop Input/Output Limitations

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  1. Analog Electronics WorkshopInput/Output Limitations Rev 0.2 March 13, 2013

  2. What’s Wrong?

  3. Common Mode Voltage Definition

  4. Input and Output Swing Vcm Range Output Swing Vcm Vout

  5. Vcm – Two Examples Vcm = 0V Vcm = 5V

  6. Input Stage Output Stage VSAT VBE

  7. Translating the Data Sheet -2.6V< Vcm < 1.0V -2.45< Vout < 2.45V -2.6V< Vcm < 1.0V

  8. Vcm or Output Swing Problem? Vcm=Vin! • Remember • -2.45V<Vout<2.45V • -2.6V<Vcm<1.0V • What is the common-mode voltage? • This is a Vcm violation!

  9. Vcm Lab • Measurement

  10. NI myDAQ Exercise-Vcm Populate U1 with OPA735 Set J2 to 1-2 position

  11. NI myDAQ Exercise-Vcm • Launch Scope • Scope Settings • Scale V/Div = 500mV • Time/Div = 200us • Trigger Type = Edge • Run

  12. NI myDAQ Exercise-Vcm • Launch FGEN • FGEN Settings • Triangle Wave • Frequency=1kHz • Amplitude=4Vpp • Signal Route=AO(1) • Run

  13. Further Reading

  14. NI myDAQ Exercise-Vcm TINA Results Lab Results

  15. Output Swing Lab • Simulation • Measurement

  16. TINA Exercise

  17. TINA Exercise • Vin Settings • Triangular Wave Settings

  18. TINA Exercise • Analysis->Transient • View->Separate Curves

  19. Vcm or Output Swing Problem? Vcm=0V! Output Swing Violation! • For OPA277 • -2.0V<Vout<1.3V (RL=10k) • -0.5V<Vcm<0.5V • What is the common-mode voltage? • We can’t violate Vcm in this configuration!

  20. NI myDAQ Exercise-Output Swing • Populate U2 with OPA277 • Inverting Configuration

  21. NI myDAQ ExercisesOutput Swing • Stop Scope • Settings • Source=AI(1) • Scale V/Div = 500mV • Time/Div = 200us • Trigger Type = Edge • Run

  22. NI myDAQ ExerciseOutput Swing • Stop FGEN • Settings • Triangle Wave • Frequency=1kHz • Amplitude=160mVpp • Signal Route=AO(0) • Run

  23. NI myDAQ ExerciseOutput Swing TINA Results Lab Results

  24. I/O Limits Homework

  25. 1. For the circuit below: The output reads -260mV. The offset is 30uV typical. Why is the output so large?

  26. 1. For the circuit below: The output reads 171mV. The offset is 30uV typical. Why is the output so large?

  27. Revisions • 0.2 • Added homework • Added Lis / Kay presentation on limits.

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