1 / 33

Op Amp Offset Voltage AEW-0100

Op Amp Offset Voltage AEW-0100. Rev 1.2 Aug 2013. Input Offset Voltage. Input Offset Voltage. Offset Voltage Spec. and Distribution. Simulate Input Offset Voltage Look at the Test Conditions. OPA835. OPA835. Drift Slope – Positive and Negative. For this example Vos drift is defined:.

nhu
Download Presentation

Op Amp Offset Voltage AEW-0100

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Op Amp Offset VoltageAEW-0100 Rev 1.2 Aug 2013

  2. Input Offset Voltage

  3. Input Offset Voltage

  4. Offset Voltage Spec. and Distribution

  5. Simulate Input Offset VoltageLook at the Test Conditions

  6. OPA835 OPA835 Drift Slope – Positive and Negative For this example Vos drift is defined:

  7. Drift Slope – Common Definition

  8. Application Example

  9. Input Offset Drift Calculations

  10. Range of Offset uV to mV

  11. Input Bias Current and Drift

  12. Input Bias Current Input offset current: Ibos = Ib1 – Ib2 = 210nA – 150nA = 60nA

  13. Simple Bipolar (No Ib Cancelation) Bias current in Bipolar amplifiers is from Base Current. It is typically larger then FET and it flows into the input terminals.

  14. Bipolar with Ib Cancelation The input bias currents are mirrored and summed back in to cancel the bias current. This has the effect of significantly reducing input Ib. Note that when this is done, Ib can flow in both directions. Also Ibos is no longer smaller then Ib. Ibos = Ib1 – Ib2

  15. Bias Current for CMOS Bias current in MOSFET amplifiers is mainly from leakage into ESD diodes.

  16. OPA350 OPA277 Ib Over Temperature CMOS amplifier: In this case you see a dramatic increase in bias current at 25C. Note the logarithmic graph. Doubles every 10C. Bipolar amplifier: In this case you see a dramatic increase in bias current at 75C

  17. Range of Bias Current

  18. Ib CalculationOPA211 At High Temp

  19. Offset Lab • Simulation • Calculation • Measurement

  20. Ex 1.1: Hand Calculations 1. Use the circuit and the excerpt of the data sheet below to calculate the maximum and tpical offset form vos.

  21. Ex 1.1: Solution to Hand calculation This term is negligible Simplified equation has nearly the same result

  22. Ex 1.1: Solution to Hand calculation

  23. Ex 1.1: Solution to Hand calculation

  24. Ex 2.1: Offset Schematic Two copies of the same two stage amplifier is on the board. Each two stage amplifier has four jumpers to configure the circuit.

  25. Ex 1.1: Noise and Offset PCB Setup U0 = OPA2211 U1 = OPA2188 Note for this experiment Rin will be shorted. For the next experiment Rin will be connected between input and GND.

  26. Ex 1.1: Instrument Setup OPA211 OPA188 211: 127mV 188: 54mV The instrument setup above will configure the signal source and scope for the circuit below so that we can see the I/O limitations.

  27. Ex 1.1: Expected Results 1. Run a “analysis>dc analysis> calculate nodal voltages>” simulation to determine output offset. 2. How did the simulated results compare to the hand calculated results.

  28. Ex 1.2: Hand Calculations (with Rin) 1. Use the circuit and the excerpt of the data sheet below to calculate the maximum and tpical offset form vos.

  29. Ex 1.2: Solution to Hand calculation

  30. Ex 1.2: Solution to Hand calculation

  31. Ex 1.2: Amplifier I/O PCB Setup Change the Rin jumper settings.

  32. Ex 1.2: Expected Results 1. Run a “analysis>dc analysis>calculate nodal voltages>” simulation to determine the output voltage from vos. 2. How did the simulated results compare to the hand calculated results.

  33. Thanks for Your Time! Please try the Quiz.

More Related