Analog Electronics Class 3 Vosi, Vois Drift, Ib, Ib Drift, Ibos

1. Analog Electronics Class 3Vosi, Vois Drift, Ib, Ib Drift, Ibos Sep 20, 2011

2. Statistics Review

3. Gaussian (or Normal) Distribution 68% within ±1 standard deviation 99.7% within ±3 standard deviations

4. Single Ended Limit A typical MIN and MAX range is at least +/-3σ: Mean = Typical MAX = Mean + 3σ (or greater) MIN = Mean - 3σ (or greater)

5. Double Ended Limit Symmetrical Limits: Max = 150uV is +/-150uV Mean = often approximately zero Typical = Mean + σ ≈ σ Max = + 3σ (or greater) Min = - 3σ (or smaller)

6. Yield – Percentage of devices that Pass Test

7. Yield – Multiple Tests Probability that two or more events occur P(A ∩ B ∩ C) = P(A) x P(B) x P(C) If we assume that we set all the limits to +/-3σ What is the probability that we see a failure for five (5) different tests: P = (0.997) (0.997) (0.997) (0.997) (0.997) = (0.997)5 = .985 98.5% or a 1.5% chance of failure. For a quad device (four times the number of parameters): P = = (0.997)20 = .941 94.1% or a 5.9% chance of failure

8. Production Worthy Test Limits

9. Transistor Review

10. NPN Bipolar Transistor NPN Transistor – Current Controlled Device Ic = Ib x β Ie = Ib + Ic Vbe = +0.7V typical BVceo = Collector Emitter Breakdown voltage, base open BVebo = Emitter Base Breakdown Voltage Collector Open

11. N-Channel Depletion Mode JFET N-Channel Depletion JFET Transistor – Voltage Controlled Device Vgs_off = Negative Voltage (no current) Vgs max = 0V (maximum current) Vp = Pinch off Voltage Which determines Triode Region (ohmic region) Vp < Vgs < 0V, Vds < Vgs - Vp Saturation Region (pinch-off region) Vp < Vgs < 0V, Vds > Vgs - Vp

12. N-Channel Enhancement Mode MOSFET Don’t over voltage gate to source junction N-Channel JFET Transistor – Voltage Controlled Device Vgs_off = Negative Voltage (no current) Vgs max = 0V (maximum current) Vp = Pinch off Voltage Which determines

13. LM741 Op-Amp Schematic

14. Simplified Op-Amp

15. Short Overview of Common Mode Voltage

16. Short Overview Of Common Mode Voltage (Vcm) Vcm is the average voltage on the inputs of the op-amp. If the op-amp is closed loop the voltage is approximately the same on both inputs. More detail next class!

17. Percent Error Calculation

18. Two Definitions Common Def Measurement Def Note: The sign of the error tells you if your measured result is greater or less then expected. A common error is to ignore the sign or reverse the order of measured and Ideal.

19. What is the error? Common Def Measurement Def

20. Op Amp Power Supply

21. IQ – Supply Current With No Load IQ No Load

22. Data Sheet Specification Table The power supply current is typically 17uA, maximum 25uA at 25C with no load connected.

23. Data Sheet Specification Table The power supply current is a maximum 28uA from -40C to 125C with no load connected.

24. Absolute Maximum Ratings Exceeding maximum ratings will cause permanent damage to the device.

25. Absolute Maximum Ratings

26. Another Example OPA277 +/-15V is a 30V supply. If you exceed 36V you will damage the device. Also note the “operating range” specification of ±18V

28. OPA333 OPA277

29. Iq + Output Current IAM2 = Iq + Iout = 415uA + 5.05mA = 5.465mA

30. Iq + Output Current (low Rf) IAM1 = Iq + Iout = 415uA + 10mA = 10.415mA

31. Iq + Output Current (low Rf, No Load) IAM1 = Iq + Iout = 415uA + 5mA = 5.415mA

32. Input Offset Voltage and Drift

33. Input Offset

34. OPA333 OPA333

35. OPA827 OPA827

36. How is Vos Defined, Simulate it!

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

38. Drift Slope – Common Definition

39. OPA827 Drift Slope – Positive and Negative(common definition) • Absolute value makes all results positive. • Actual drift may be positive or negative.

40. OPA277 Warm Up Typical offset = 10uV Initial error is 10% of typical.

41. Application Example What is the percentage error?

42. Input Offset Drift Calculations

44. Input Bias Current and Drift

45. 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. Input offset current is the difference between the two currents. It is typically smaller then Ib for this simple configuration. Ibos = Ib1 – Ib2

46. 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

47. Bias current in MOSFET amplifiers is mainly from leakage into ESD diodes.

49. OPA277 OPA333 CMOS Chopper amplifier: In this case the bias current is not strongly effected by temperature. Bipolar amplifier: In this case you see a dramatic increase in bias current at 75C

50. OPA350 OPA333 CMOS amplifier: In this case you see a dramatic increase in bias current at 25C. Note the logarithmic graph. CMOS Chopper amplifier: Shows that Vcm has an effect on Ib.