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It's actually not an audio amplifier but a variable gain amplifier (for biosignals) which employed an input cap array, a feedback cap and a feedback resistor. Unfortunately, I'm past the deadline to change anything, just need to explain why I discarded the input cap array and used a variable...
Hey guys, thank you for your replies. I should have mentioned that I wanted to use a capacitor array in front of the input of the amplifier and the different capacitors are supposed to be shortable using switches (simple PMOS Transistors, which are then in the signal path). Is it still the right...
Hey guys,
could someone explain to me, why it is not sensible to use switches at the input of an amplifier. I was told to be careful with it but not why. Do they generate noise or distort the signal or sth. like that?
Thanks,
Arielle
Hi,
can someone please explain to me why the input-referred noise of the overall amplifier is given by that expression:
for such a feedback structure? Cp is the parasitic capacitance from the input transistors of the OTA. This information is taken from a book and I don't understand especially...
Wow O.O I would never have come to such a solution but I will try to understand it, perhaps I will ask you again while working through it (it looks quite complex). In any case you really helped me a lot, so thank you very very much!
Wow, I have pretty much the same problem! But I don't really understand how you get to your solution, is there a structured way to come to the transfer function? why is there a s^2 in the numerator? I did just use that formula:
TF = -(Z2/Z1)*1/(1 + 1/A + Z2/(Z1*A)) and use Z1 = 1/(s*C1); Z2 =...
So... in the attachment you can find the things I tried. The one buffer that works best but consumens 4 times the current of my opamp is actually connected to my opamp right now.
Perhaps one of you can judge better than me which buffer has a chance to work best for my specifications:
I want no...
Yeah, right... tomorrow morning when I have access to the program again, you can have a look at all the things I tried. Not a problem for me, just a lot of work for whoever wants to help me.
Oh my ***... everytime I post sth. I feel super stupid here and by now I truly hate electronics... I just have to stick to it a couple of months more before it will be over forever... but nevermind it: I would immediately add a second stage to my single stage if I'd understand why such a thing...
Hi guys,
it's me again... with another question: I use resistive feedback to have a variable gain. Therefore I need a buffer at the output of my opamp. Until now I have an ideal buffer but the problem is that the real buffer should not have a dc level shift (like source follower) and it should...
Hi guys, just wanted to say that it's finally working & thank you very much for your help. After I inserted a buffer (instead of a second stage hahaha), it worked out =)
@LvW: sry, my screenshot was bad because it didn't show that I had actually a signal at the second input, so it's not open
Hey, thank you two! I tried to do as you said (see screenshot) and I think that my gain can be set by Rfb/Rin now. However, my phase is... not what I expected and if I apply larger AC signals than 1mV at the input, my output common mode goes up. I made pictures and hope, you can tell me what I...
Hi guys,
I have a very fundamental problem: First, is it possible to use resistive feedback on a circuit as shown in the picture? When I tried to simulate it, the bode plot had a very odd form and the DC gain I calculated by -Rf/Rin could not be seen in the simulation results... Help pls.
Arielle
Hey,
from a paper I know that the gain of the Gilbert cell (see picture) is as follows: A = (2*gm1/(gm1+gm2)-1)*gm56*Rout. However, I'm not able to understand why, especially the first part in parentheses... Pls help me =(
Arielle
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