Advertisement

Operational Amplifiers Summary

We can conclude our section and look at Operational Amplifiers with the following summary of the different types of Op-amp circuits and their different configurations discussed throughout this op-amp tutorial section.

Operational Amplifier General Conditions

  • • The Operational Amplifier, or Op-amp as it is most commonly called, can be an ideal amplifier with infinite Gain and Bandwidth when used in the Open-loop mode with typical DC gains of well over 100,000 or 100dB.
  • • The basic Op-amp construction is of a 3-terminal device, 2-inputs and 1-output, (excluding power connections).
  • • An Operational Amplifier operates from either a dual positive ( +V ) and an corresponding negative ( -V ) supply, or they can operate from a single DC supply voltage.
  • • The two main laws associated with the operational amplifier are that it has an infinite input impedance, ( Z =  ) resulting in “No current flowing into either of its two inputs” and zero input offset voltage “V1 = V2“.
  • • An operational amplifier also has zero output impedance, ( Z = 0 ).
  • • Op-amps sense the difference between the voltage signals applied to their two input terminals and then multiply it by some pre-determined Gain, ( A ).
  • • This Gain, ( A ) is often referred to as the amplifiers “Open-loop Gain”.
  • • Closing the open loop by connecting a resistive or reactive component between the output and one input terminal of the op-amp greatly reduces and controls this open-loop gain.
  • • Op-amps can be connected into two basic configurations, Inverting and Non-inverting.

The Two Basic Operational Amplifier Circuits

basic operational amplifier circuits

  • For negative feedback, were the fed-back voltage is in “anti-phase” to the input the overall gain of the amplifier is reduced.
  • For positive feedback, were the fed-back voltage is in “Phase” with the input the overall gain of the amplifier is increased.
  • By connecting the output directly back to the negative input terminal, 100% feedback is achieved resulting in a Voltage Follower (buffer) circuit with a constant gain of 1 (Unity).
  • Changing the fixed feedback resistor (  ) for a Potentiometer, the circuit will have Adjustable Gain.

Operational Amplifier Gain

operational amplifier gain bandwidth product

  • The Open-loop gain called the Gain Bandwidth Product, or (GBP) can be very high and is a measure of how good an amplifier is.
  • Very high GBP makes an operational amplifier circuit unstable as a micro volt input signal causes the output voltage to swing into saturation.
  • By the use of a suitable feedback resistor, (  ) the overall gain of the amplifier can be accurately controlled.

Differential and Summing Amplifiers

differential and summing amplifiers

 
  • By adding more input resistors to either the inverting or non-inverting inputs Voltage Adders or Summers can be made.
  • Voltage follower op-amps can be added to the inputs of Differential amplifiers to produce high impedance Instrumentation amplifiers.
  • The Differential Amplifier produces an output that is proportional to the difference between the 2 input voltages.

Differentiator and Integrator Operational Amplifier Circuits

differentiator and integrator amplifiers

 
  • The Integrator Amplifier produces an output that is the mathematical operation of integration.
  • The Differentiator Amplifier produces an output that is the mathematical operation of differentiation.
  • Both the Integrator and Differentiator Amplifiers have a resistor and capacitor connected across the op-amp and are affected by its RC time constant.
  • In their basic form, Differentiator Amplifiers suffer from instability and noise but additional components can be added to reduce the overall closed-loop gain.

24 Comments

Join the conversation!

Error! Please fill all fields.

  • R
    Rohankumar

    My doubt Is an equation for inverting op- amp is Rf/Rs but in non-inv op- amp is 1 Rf/Rs so why 1 Is requierd

  • A
    Alka rai

    It was so help full. It helped me alot to clear all of my basic concepts.

  • a
    abdiaziiz

    what does mean ‘virtual grounded’

    • n
      nabil almarfadi

      English only

    • A
      Asim Zulfiqar

      It is the property of op-amp to keep the same potential at its input terminal so in non-inverting amplifer when the positive terminal is grounded the op-amp will try to keep the same potential at non-inverting terminal and the potential at non-inverting terminal will be 0v which is not actually connected to ground, hence called virtual ground.

  • m
    marshall mashinya

    buffer as unity gain (0db)and reproduces the input voltage.what possible use is a circuit such as this ,which offers no voltage gain or any other form of signal modification.

  • H
    Herschel

    Bias current compensation?
    Considering an inverting amplifier, I often see a resistor added from the non-inverting input to ground. The suggested value is equal to the parallel value of the other two resistors.
    I only see this in op amps with bipolar transistors on the input. Op amps that have bias currents in nA. Is this resistor just not needed in JFET input op amps with bias currents down into pA range?

  • M
    MicheleD

    Thanks for this clear introductory tutorial on OpAmps. It did, along with some other works, help me get a better understanding of OpAmps. I am left though with two rather problematic hurdles. One is that I still do not have an understanding of the pros and cons of inverting vs. non inverting amplifiers. Under what conditions should one go for one as opposed to going for the other. If you could possibly elaborate on this. The other hurdle is that I planned a strain gage application using a differential amplifier which looks good on paper but which simply does not work. I get no output on Vo. Characteristics are 1K/1M for a gain of 1000. Bridge is 4x1K balanced via a potentiometer to yield 0 volts between v+ and v-. R1=R2=1K, R3=R4=1M. V+ to ground via R4 as per your schematic. When gage is stressed (+4 ohms) I get 2.5v on V+, 2.5 + 4mV on V-. V0 stays at 0 all the time (twitches between + and – 1mV). I used both LM520 and AD822 – same bad results, VCC at +5V, VEE at 0 – common ground). I am getting to believe that amplifying 4mV over 2.5 volts is stretching the capabilities of the OpAmp and that perhaps the solution lies with an instrumentation amplifier, which I have yet to try. If you could possibly comment ?? Thanks, Michèle

  • J
    Jaliya

    Amazing teaching ability.!! Thank you very much for all your tutorials about op amps. I’m studying for an electronic exam and these are the only notes I’m studying about op amps.. Hope they will help me @ the exam hall..

  • s
    sameerkhan

    Wow.
    Thanks first to tutorial.
    Sattapadinga enakku pirayisanam irunthichi

  • M
    M I P

    A very good website for tutorials on OPAMPS

  • E
    ErIn tHoMaS

    YOUR EXPLANATION ON OP AMPS REALLY HELPED ME UNDERSTAND THE CONCEPT. THANKS WAYNE.

Looking for the latest from TI?