Op amp circuit

Discussion in 'Homework Help' started by johnjoe2000, Dec 6, 2009.

  1. johnjoe2000

    Thread Starter New Member

    Dec 6, 2009
    4
    0
    This is to do with my previous post.

    I am having difficulty understanding this circuit and i cant find information or similar diagrams anywhere.

    Basically i think that its something to do with an analogue to digital conversion, using a low pass filter and oversampling...?

    Can someone tell me if im in the right kind of area? ( i really dont know much about circuits)

    i dont want the answers to the questions... Just some general help


    thanks
     
    Last edited: Dec 6, 2009
  2. kdillinger

    Active Member

    Jul 26, 2009
    141
    3
    It is what some people would refer to as an AC-coupled amplifier. I personally don't use that terminology, but who am I?:)

    R3 and R4 form a traditional voltage divider circuit which provides a DC bias at the non-inverting input (IN+) of the op-amp. This is required because the op-amp is powered on a signal supply rail (+V and GND) and the source is audio which will be "sinusoidal" in nature meaning its amplitude will swing above and below 0V. If the DC bias was no provided at the IN+ pin, then the output will clip on the negative swing as the source will swing below 0V but the op-amp cannot go below 0V because its negative rail is GND. It cannot go any higher or lower than its own power rails.
    C2 is the coupling capacitor which blocks the source DC bias and allows the amplifier to bias to the DC voltage set by R3 and R4 as I mentioned before.
    C3 is the output coupling capacitor that removes the DC bias that was set, again, by R3 and R4.
    I confess, I am not sure why RV1 is there, it looks like a potentiometer. Typically RV1, otherwise known as the load, would be after C3.
     
  3. johnjoe2000

    Thread Starter New Member

    Dec 6, 2009
    4
    0
    Thanks very much for the information

    i am still kind of confused about it and going to have great difficulty answering the questions... Do you know of any sites that will help me answer the set questions or have similar diagrams i can study? I am very new to this ( and its an optional module not my usual course)
     
  4. kdillinger

    Active Member

    Jul 26, 2009
    141
    3
  5. kdillinger

    Active Member

    Jul 26, 2009
    141
    3
    (i) What function does the circuit provide?

    Inverting, AC coupled amplifier.

    (ii) Describe the function of each of the components in the circuit
    R1,R2 set the amplifier gain.
    R3,R4 set the amplifier DC bias.
    C2,C3 are DC blocking capacitors.

    (iii) What change would you make to this circuit to turn it in to a unity gain amplifier? State suitable values for any components you change or add to the circuit.
    Set R1=R2 then it will be a unity gain inverting AC coupled amplifier.

    (iv) What change would you make to the circuit to turn it into a simple two-input mixer? State suitable values for any components you change or add to the circuit.
    Add another series capacitor and resistor and connect to the IN- node for a summing circuit.

    (v) What change would you make to the circuit to turn it into a low pass filter? State suitable values for any components you change or add to the circuit.
    Add a capacitor across R2.

    Give your opinions of the relative merits of op-amp-based circuits compared to discrete component-based circuits (i.e. where individual transistors and components are utilised to prove signal gain and processing).
    Monolithic op-amps provide precision matched internal components for better quality. --- kind of BSing but close enough.
     
  6. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Why do you make so many threads about this simple amplifier?????
     
Loading...