Hi again!
I was reading the following link:
In page 16-12 (Figure 16-12) they are showing a first order non-inverting low pass filter. I tried calculating the transfer function and came up with the following:
Vo / Vin = (1 + R2/R3) / ( s*C1*R1 + 1 )
Their transfer function is:
Vo / Vin = (1 + R2/R3) / ( wc*s*C1*R1 + 1 ), wc = omega sub c (I think this represents the cut off frequency).
My question is: how did they get wc?
Thanks!
Your transfer function is correct. They are wrong.
It's a mistake. s = jwc
Graham
It's not wc (omega times c); it's omega sub c. Go back and read page
16-2, where they say:"For a normalized presentation of the transfer function, s is referred to the filter's corner frequency, or - 3dB frequency, w sub c, and has these relationships:"
Yep, I actually wrote down wc = omega sub c. Thanks for pointing out that page. I'm going to re-read it again and see if I can understand it. I'm not too comfy about s = sRC. To me, it's like saying 1 = 1*2*3.
I would definitely agree. I would have made up a new symbol for the normalized s, something like s' or s sub n or something. It's very bad practice to use the same symbol for two different things!
I think I would just rewrite all the pertinent equations with a different symbol for normalized s before I tried to follow the analysis.
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