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Apologetic First Thread, its a Uni One


Oct 18, 2013
Oct 18, 2013
Sorry for presenting you guys with another thread from a uni student seeking advise/help.
I'am an electrician by trade, now attempting to become an electrical engineer. I know control system circuits and so on good, but at designing electronic circuits, I'am a noob, so please be gentle lol
Here we go.

We are required to design a circuit where the output is isolated from the input by an opto-coupler that is constructed from discrete components, an IR LED (QED123 - fairchild electronics) and a Photo Transistor (QSD123 - fairchild electronics)
The input signal to the circuit is specified as 2 +Asin(2*pi*f*t)V where 20Hz<f<20kHz and
1<A<4 V.

The design specifications are:
1. The output signal is to be 2Asin(2*pi*f*t + Theta)
2. The phase shift, Theta, with respect to the input signal, must be as small as possible

The opto-coupler was constructed and given to us. We are only allowed one, and it only has one photo transistor in, so linear feedback using one of them is not possible.
We can use LM741 opamps, resistors, capacitors, diodes,LED's, and other ancillary components.

So here is the circuit I designed. Any thoughts(serve it to me if i have done it bad), opinions, advise on how to make it better, hints etc is most welcome. Btw, I know the supplies for the primary and secondary side opamps should be separate, but I was just being lazy when I did that.

Primary Side.jpg
Secondary Side.jpg

And here is an image of the Bode Plot of the output as simulated in LT spice.

Bode Plot.jpg,

I was wondering if i can improve the gain and phase shift in the upper 10Khz, but i don't know how to go about doing that.

For those who give this a look over and a helping hand, thanks.