need help in designing an Operational Amplifier circuit

[walid66]

Hello
I need your help in designing an Operational Amplifier with these conditions:
The i/p signal changing from Vmax= 80 mv to Vmin=60 mv, the o/p must be Vout = + 5 V when Vmax= 80 mv and Vout = - 5 V when Vmin=60 mv
thank you very much

 

[MikeMl]

For starters, the gain must be (5 - (-5))/(0.08 - 0.06) = 10/0.02 = 500

Since it requires non-inverting gain, either split it into two inverting amplifiers, such that -G1* -G2 = 500, e.g. G1 =-20 and G2=-25 (better), or try to get all of the gain in one opamp stage (poor design).

If using only one stage, the high frequency performance will suffer because opamps don't do well at such high gains. Also, the intrinsic offsets in opamps get multiplied by the stage gain, so you will need a trimpot to set the offset. Splitting the design into two stages makes the offset problem more manageable.

What type of opamps? What supply voltage(s)? How well regulated are the supply voltage(s)? What drift are willing to tolerate? What does the frequency response need to be? Is this a homework assignment?

 

[walid66]

For starters, the gain must be (5 - (-5))/(0.08 - 0.06) = 10/0.02 = 500

Since it requires non-inverting gain, either split it into two inverting amplifiers, such that -G1* -G2 = 500, e.g. G1 =-20 and G2=-25 (better), or try to get all of the gain in one opamp stage (poor design).

thank you very much
i'm not understand, can you put a drawing to take a look at the idea, please

If using only one stage, the high frequency performance will suffer because opamps don't do well at such high gains. Also, the intrinsic offsets in opamps get multiplied by the stage gain, so you will need a trimpot to set the offset. Splitting the design into two stages makes the offset problem more manageable.

What type of opamps? What supply voltage(s)? How well regulated are the supply voltage(s)? What drift are willing to tolerate? What does the frequency response need to be? Is this a homework assignment?

yes it is a homework assignment and i'm free in choosing opamp, supply etc
please help me
thank you very much

 

[MikeMl]

I want you to learn something; not just hand a complete answer to you!

Here is the basis of the answer. Note that in the circuit below, as V2 sweeps from 40mV to 60mV, the output goes from -5V to +5V, similar, but not the same as your specs...

E2 is a Voltage-controlled Voltage Source with an open-loop gain of 1,000,000. You can think of it as an ideal op-amp. No bias current, no offset, high open-loop gain, infinite gain bandwidth product, infinite output current, zero output impedance, etc. Note that it amplifies (V(+) - V(-) by 1 million. Another way to say it is that V(+) essentially = V(-).

I will leave it you to justify why R2/R1 = 499, and why V1 = 50.1002mV.

 

[crutschow]

Also, the intrinsic offsets in opamps get multiplied by the stage gain, so you will need a trimpot to set the offset. Splitting the design into two stages makes the offset problem more manageable.

Since the first op amp offset is multiplied by the total gain in a DC amp, I don't see how adding a stage affects the offset problem.