Presentation is loading. Please wait.

Presentation is loading. Please wait.

The Operational Amplifiers Dr. Farahmand. Opamps Properties IdealPractical ArchitectureCircuits Open Loop Parameters Modes of operation Frequency Response.

Similar presentations


Presentation on theme: "The Operational Amplifiers Dr. Farahmand. Opamps Properties IdealPractical ArchitectureCircuits Open Loop Parameters Modes of operation Frequency Response."— Presentation transcript:

1 The Operational Amplifiers Dr. Farahmand

2 Opamps Properties IdealPractical ArchitectureCircuits Open Loop Parameters Modes of operation Frequency Response Closed Loop Frequency Response Negative Feedback Inverting Non- inverting 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 (  t) 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) A OL(mid )

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

12 Open Loop Frequency Response For multiple stages  total = ...... 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 NoiseWith 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/A ppl_OpAmps2.html http://www.chem.uoa.gr/Applets/AppletOpAmps/A ppl_OpAmps2.html – http://www.falstad.com/circuit/directions.html http://www.falstad.com/circuit/directions.html


Download ppt "The Operational Amplifiers Dr. Farahmand. Opamps Properties IdealPractical ArchitectureCircuits Open Loop Parameters Modes of operation Frequency Response."

Similar presentations


Ads by Google