@The Electrician - thank you for that information.
I got there now, i am quite happy with my result
I also realized I was trying to resolve the magnitude of the complex numbers instead of just using the excel functions available (i don't have any software like MATLAB or mathcad whch...
Great - thank you for pointing out that this was incorrect or i'd have used the wrong circuit.
When I have the s term, how do I derive a value for this for a bode plot if it is based on an imaginary term?
That could very well be my issue - i am glad I know what I did wrong but unfortunately I only know I did wrong on the wrong circuit anyway :smile: :headbang:
I found this paper on designing them https://www.irjet.net/archives/V2/i5/IRJET-V2I5143.pdf
This may be very helpful to me but I need to fully understand the relationship between s=jw. Imaginary numbers are very new to me and have caused me quite a bit of trouble so far.
The circuit I posted does actually also appear in this paper as a sallen-key bandpass filter
http://sites.bu.edu/engcourses/files/2016/08/ActiveFilterNotes.pdf
my task is to design a sallen key band pass filter with an fo value of around 3.3k and a Q factor of 2.2. I believe my main objective is not the design of the circuit itself but to come up with the capacitor and resistor values for those requirements
this topology appears in my course notes...
I have the above transfer function for this filter design
The transfer function becomes
which then becomes
Now when I try to use this transfer function to plot a bode plot, I always end up with negative terms which i can't get the square root of
For example, at 1hz, where
w = 6.283
R1 = 1705...
Yeah maybe but this was 2 weeks ago :biggrin:
No big deal anyway and it's not like I harassed him or anything, just asked him and moved on when he didn't reply.
Ok thank you - I had actually already sketched it by hand and asked my lecturer if this was enough, but he didn't reply and I assumed that meant he was unhappy with the question :D
I will go with the hand sketch as I know how they should look anyway. Thanks everyone for your time.
Do I just make up values for the resistors and capacitors though? I don't understand how to calculate the gain at a certain frequency without replacing the values in the transfer function with actual numbers?
Hi
Can anyone help with this? I understand what the bode plots should look like but I am not sure how to produce a plot in excel for them without any values
The transfer functions are:
Vout/Vin = 1/(SQRT(1+(ω/ωc)^2)
and
Vout/Vin = -G/(1+j(ω/ωc))
As both are first order filters they will have...
It's really interesting to see just how many ways there are to solve it. Seeing how Dave and the electrician both solved it differently was very cool, but also way above my level.
About the complex maths part of it - I'm not asking for an explanation of how to do this but I thought with...
Thank you!
Yes I'd be interested to see that if you have the time. I find this method of learning much better than simply reading pages and pages of notes