1 / 20

The Operational Amplifiers

The Operational Amplifiers . Dr. Farahmand. overview. Operational Amplifiers. Historically built using vacuum tubes and used for mathematical operations Today, opamps are linear integrated circtuis (ICs) Terminal Inverting and non-inverting inputs Dc supplies Single output. Opamps.

gavivi
Download Presentation

The Operational Amplifiers

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. The Operational Amplifiers Dr. Farahmand

  2. overview

  3. Operational Amplifiers • Historically built using vacuum tubes and used for mathematical operations • Today, opamps are linear integrated circtuis (ICs) • Terminal • Inverting and non-inverting inputs • Dc supplies • Single output

  4. Opamps • Ideal opamps • Infinite BW • Infinite voltage gain • Infinite input impedance • Zero output impedance • Practical opamps • wide BW • Very high voltage gain • Very high input impedance • Very low output impedance

  5. Architecture • 3 stages • Differential amplifier input stage: • Take the difference between the input signals • If the input base voltage is different: • Vb1 > Vb2 • Ic1 > Ic2 • VRc1 > VRc2 • Vc1 < Vc2

  6. Modes of Operations • Differential amplifiers can be connected in difference ways • Single-ended mode • Single input • Differential mode • Out of phase inputs • Unwanted noise on both inputs is cancelled • Common mode • In phase inputs

  7. Parameters • Common mode input voltage • Input voltage range limitation • Typically +/- 10 V with dc voltages of +/- 15 V • Input offset voltage (in mV) • Differential dc voltage required between the inputs to force the output to zero volt • Input bias current (in nA) • Dc current required by the inputs of the amplifier to properly operate the first stage ( Ibias = (I1 + I2)/2 ); I1 and I2 are the current into inverting and non-inverting inputs • Input impedance (in Mega ohm) • Total resistance between the inverting and non-inverting inputs • Output impedance (in ohm) • Total resistance at the output • Slew rate (in V/usec) • How fast the output voltage changes in response to the input voltage change

  8. Parameters • Common mode input voltage • Input voltage range limitation • Typically +/- 10 V with dc voltages of +/- 15 V • Input offset voltage (in mV) • Differential dc voltage required between the inputs to force the output to zero volt • Input bias current (in nA) • Dc current required by the inputs of the amplifier to properly operate the first stage ( Ibias = (I1 + I2)/2 ); I1 and I2 are the current into inverting and non-inverting inputs • Input impedance (in Mega ohm) • Total resistance between the inverting and non-inverting inputs • Output impedance (in ohm) • Total resistance at the output • Slew rate (in V/usec) • How fast the output voltage changes in response to the input voltage change (Dt) Refer to Table 12-1

  9. CMRR • Common-mod-rejection ratio (CMRR) • The measurement of how the amplifier can reject common more signals • CMRR = Open loop voltage gain / Common mode gain • Often expressed in dB • The larger the better From data sheet Ideally zero/ indicate how much of input noise is passing through

  10. Open Loop Frequency Response • Aol(OL) : Open loop gain In practice Vmid = Vin x AOL(mid) AOL(mid)

  11. Open Loop Frequency Response Frequency response: Aol(OL) = Aol(mid) Critical frequency is the roll-off point Phase response: q = -arctan (R/Xc) = -arctan (f/fc) Delay = Period x Phase shift / 360

  12. Open Loop Frequency Response For multiple stages qtotal = q1 + q2 + q3 + ...... Av(dB) = Av1 + Av2 + Av3 + ….

  13. Closed Loop Frequency Response • Non-inverting • Source is connected to the non-inverting input • Feedback is connected to the inverting input • If Rf and Ri are zero, then unity feedback used for buffering • Vo= • Inverting • Feedback and source are connected to the inverting input

  14. Comparators • Determines which input is larger • A small difference between inputs results maximum output voltage (high gain) • Zero-level detection • Non-zero-level detection Max and minimum

  15. Example Vref = Vin(max).R2/(R1+R2)=1.63 V

  16. Comparator – Impact of noise (unwanted voltage fluctuation) No Noise With Noise Inaccuracy!

  17. Hysteresis(Schmitt triggers) • Making the comparator less sensitive to the input noise • Effectively higher reference level • Upper Trigger Point • Lower Trigger Point VUTP = Vout(max).R2/(R1+R2) VLTP = -Vout(max).R2/(R1+R2) VHYS= VUTP – VLTP

  18. Zener Bounding • The output voltage can be limited using Zener diodes • Vout >0  Vz • Vout < 0  Forward biased (0.7) • Note that the output signal is inverted Virtual Ground

  19. ? Zener Bounding • Combined effect Bounding the negative values /

  20. Resources • Applets • http://www.chem.uoa.gr/Applets/AppletOpAmps/Appl_OpAmps2.html • http://www.falstad.com/circuit/directions.html

More Related