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Op Amp Nonidealities (1)

Op Amp Nonidealities (1) . Section 8.4. Topics. DC Offset Input Bias Current Speed Limitations Slew Rate Finite Input and Output Impedance. DC Offset. V io for ST UA741 CN is 1 mV (Typ.) Cause of offset: mismatch during fabrication. Symptom of DC Offset.

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Op Amp Nonidealities (1)

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  1. Op Amp Nonidealities (1) Section 8.4

  2. Topics • DC Offset • Input Bias Current • Speed Limitations • Slew Rate • Finite Input and Output Impedance

  3. DC Offset • Vio for ST UA741 CN is 1 mV (Typ.) • Cause of offset: mismatch during fabrication

  4. Symptom of DC Offset • Symptom: Vout is not zero when Vin2-Vin1=0 • Vos can appear at either input with arbitary polarity.

  5. Problems Caused by Input Offset Voltage Offset amplified by the gain!

  6. Saturation Caused by DC Offset Offset of 1 mV Gain=100 Gain=100 What is the gain of this amplifier? Assume an offset of 1 mV.How much offset appears at X? 100 mVHow much offset is expected at Vout? Saturation

  7. Input Bias Current Iio is 10 nA for ST UA741 CN

  8. Problem Caused by Input Bias Current IB1 has no effect Replace by Thevenin eq. circuit Feedback caused the voltage drop across R2 to be 0

  9. Input Bias Current Correction Parallel combination of R1 and R2 added in order to cancel offset at the output due to input bias current

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