Good morning!

I have designed a filter which can reduce dynamic error in measurement systems which exhibit first-order behaviour. I have proven the ideal case using PSpice simulation, now I would like to test the circuits response to noisy input.

From google it would appear that using the AC Sweep/Noise simulation and enabling "Noise Analysis" should do the job. I have attempted to do this but the simulation results are identical to the ideal case.

I am unsure if I have set this up correctly, the link below is a screenshot of the circuit and simulation profile (I won't embed as it's large);

http://i496.photobucket.com/albums/rr326/pdunc/first_order_comp-1.jpg

Does anyone have experience of testing a schematic with noise? I am expecting to get some noise amplification through the system.

Thanks in advance,

Peter

 

The LM324 quad opamp is very noisy, has a poor high frequency response and has severe crossover distortion.
Your circuit has low frequencies cut twice and low frequencies boosted one time. Why?
It has two inverters and a useless opamp so maybe a dual opamp can be used.

 

Thank you for your response, Audioguru.

These are indeed considerations I will need to take into account for the final design.

To explain what things are doing at present...

-The initial RC circuit is to simulate my input signal; which will be a voltage from a temperature transducer with first-order behaviour.

-The unity-gain buffer here is self explanatory.

-The next filter is used to 'extend' the frequency response of the input signal, meaning when the two signals are convolved we should see a faster response time. A by-product of this is signal inversion.

-The unity gain buffer here is pointless and will be removed.

-The final op-amp simply inverts back to the correct polarity.

Hopefully that gives a better idea of what I am trying to achieve. Although none of the above helps with my current problem of simulating a circuit with noise in PSpice.

Do you have any experience of this?

Thanks again,

Peter

 

I use low noise TL071 single, TL072 dual and TL074 quad low noise very low distortion audio opamps.
I saw a very noisy distorted LM324 in a speakerphone that was made in Korea and sounded awful.

I don't think PSpice knows anything about noise.

 

I had built a test circuit with the LM324 and this had poor results - the characteristics were correct, but a number of errors were introduced.

This is project work for university so the errors are good for discussion points, but I have ordered in a TL074 to try to gain accuracy for the final built.

Thanks again,

Peter