Accuracy Of Design

Have you built these three designs or are they simulated?

Simulated and real world designs will differ slightly due to tolerances in your components and how they change under various circumstances, like increasing temperature. Resistors and capacitors chosen in simulation cannot always be easily chosen in real world designs as manufacturing every single possibility of resistor would be pointless. Instead ranges based on tolerance are manufactured, meaning real world designs might be slightly different.

If you haven't built it, it might be an idea to have a look at what actual components you would use if you were to build it and the tolerances attached to these components to show how accurate your design is.

Hope this helps in some way.

Hello,

Thanks very much for your information. Yes i have designed, built and tested all three circuits. I guess with the resistors the tolerance on these at 5% could be improved by using 1% resistors?

The main idea behind this was that i was given a specific gain so it was all based around that value.

Just off the track, if a summing amp with two inputs happen to have the same resister say 1k will the measured gain be the same as each other?

Yes, using 1% would improve accuracy alright.

Yes the measured gain should be the same as each other.
But given the 5% tolerance of the resistors, one resistor could be 995 ohms and the other could be 1005 ohms, giving slightly different gains. Manufacturing guarantees the resistor be in between 995 ohms and 1005 ohms, but cannot guarantee two resistors being exactly identical. You can increase the tolerance to 1%, 0.1%, maybe even 0.01% to reduce the difference, but the cost increases significantly for these resistors.

hi,

since you have built it and have proven that it it functions, you might as well include in your commentaries voltage/current you have measured at specific points.

There are principally two methods with pencil/paper/calculator:

1) Sensitivity analysis
2) Amplifier parameters

For sensitivity analysis, yes it includes absolute tolerance but also temperature tolerance. For amplifier parameters you principally have two things to deal with, that is input-offset current, input-offset voltage.

I have separated the temperature effects from the amplifier parameters which is only simplistic. You certainly need consider temperature effects on the amplifier as well as long term drift for all components.

You need to specify what sort of accuracy you need if you want. This can help to either simplify or make more accurate the prediction.

I can send you a guide line on how to do this. It's not that hard and I believe I have one in a spreadsheet format that helps keep tabs

Hello rick,
Since you are using passive components like resistors & capacitors in your circuit you can't make the circuit more accurate, as capacitors have been used the value of capacitor is always less than as specified on it's cap. Like a 33pf capacitor will not have the capacitance of 33pF, but will be preety much less than 33pF practically, so i suggest u to use capacitors in uF range like 0.1uF.
you can have choice of opamp for accuracy, like if you want a better accuracy (High CMRR, less offset voltage & current) you can use OP-07.

Hope this will help.
All the best!

Hi,

yeah i have record all my measurements for the three circuits. I have had seperate questions for these. I guess all i can do is compare to different op amps, components.....

Yeah any information is welcome in my book... please send ...

Gogh