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Instrumentation Amplifiers

Instrumentation Amplifiers. Block diagram of a biomedical instrument. Instrumentation amplifier provides differential amplification. Input 1. Input filter. To: ADC Instrument Screen Etc. Differential amp. More amp. More filtering. Input 2. Input filter. Instrumentation amplifier.

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Instrumentation Amplifiers

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  1. Instrumentation Amplifiers 415-5

  2. Block diagram of a biomedical instrument Instrumentation amplifier provides differential amplification Input 1 Input filter To: ADC Instrument Screen Etc. Differential amp More amp More filtering Input 2 Input filter 415-5

  3. Instrumentation amplifier Input buffers Differential amplification 415-5

  4. Gain of the instrumentation amplifier i 415-5

  5. 415-5

  6. How is the gain set? Choose RG 415-5

  7. Note on ≤1% tolerance resistors 415-5

  8. What is the bandwidth? Note that gain*BW is not constant 415-5

  9. Gain revisited 415-5

  10. How is the common-mode performance? CMRR – common-mode rejection ratio 415-5

  11. More expensive IA have higher CMRR and lower tolerance resistors A laser “trims” the internal resistors while still on the wafer until they are within tolerance. More time spent trimming gives better CMRR but higher cost. 415-5

  12. Biopotential amplifier 415-5

  13. What does the input circuitry do? • Diodes for protection • Resistors and capacitors for filtering • Analyze corner frequencies for prelab • Save or rebuild this circuit for ECG lab 415-5

  14. Amplifier resources • Analog Devices Designer's Guide to Instrumentation Amplifiers (http://www.analog.com/static/imported-files/design_handbooks/5812756674312778737Complete_In_Amp.pdf) • Analog Devices Op Amp Applications Handbook (http://www.analog.com/library/analogDialogue/archives/39-05/op_amp_applications_handbook.html) • TI Op Amps for Everyone Design Guide (http://focus.ti.com/general/docs/litabsmultiplefilelist.tsp?literatureNumber=slod006b) • Maxim Amplifier Tutorials index (http://www.maxim-ic.com/tarticle/article.cfm#3) • National Semiconductor An Application Guide for Op Amps (http://www.national.com/an/AN/AN-20.pdf) • National Semiconductors A Basic Introduction to Filters (http://www.national.com/an/AN/AN-779.pdf) 415-5

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