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One thing to have in mind is that OpAmp have an limited gain, and its gai=
n
it's lower with the frequency rises, ie, the graphic gain vs. frequency i=
s
kind of:    Gain (V/V) =3D DC_Gain - Frequency*k        where k is a cons=
tant.
It's hard to explain in words, but is something like that: In DC the gain=
 is
(for example) 1E6; at 1kHz is 1E5; at 100kHz is 1E4; at 10MHz is 1E3; 100=
MHz
is 1E2 and so on....=0D
    When you use a resistors to set the gain for example to 1E3, it will
work only from DC to 10MHz, ....=0D
=0D
    I don't know if I could help, but I've tried,=0D
=0D
God Bless you,=0D
=0D
Jonnathan Partamian=0D
=0D
-------Mensagem original-------=0D
=0D
De: pic microcontroller discussion list=0D
Data: Quinta-feira, 20 de Fevereiro de 2003 22:23:53=0D
Para: PICLIST@MITVMA.MIT.EDU=0D
Assunto: [EE]: Differential Amplifiers=0D
=0D
Hi guys,=0D
=0D
I have a generalised op-amp question. I am having trouble trying to=0D
extrapolate what I need to know from manuals and datasheets, so maybe one=
 of=0D
you experts here in analog electronics (something I definately am not) ca=
n=0D
help me with understanding the concept. This may seem like a dumb questio=
n=0D
to some of you, but here goes...=0D
=0D
Do op-amps have a limit on the amount they can amplify a signal ? What I =
am=0D
finding is that if you increase the difference in resistance in the divid=
er=0D
in a differential amplification setup, at a certain point, the signal=0D
becomes non-linear at the peaks. Increasing the reference voltage into th=
e=0D
op-amp does not seem to help. At a certain point in the divider value, th=
e=0D
output simply shifts further up from zero, rather than increasing the gai=
n,=0D
and the peaks are flattened out. Note that this is not the same as gettin=
g=0D
the low point to zero on a non rail-to-rail op-amp by providing a negativ=
e=0D
reference - I am already doing this. I am having a great deal of trouble=0D
getting much more than about 20x gain from an LM358. I would like 100x=0D
gain, but this seems impossible to achieve with this op-amp, even though =
it=0D
is marketted as a "HiGain" op-amp.=0D
=0D
I am pretty sure of my observations. I am not proto testing it, but SPICE=
=0D
testing it with CircuitMaker, so I can see a sine wave amplified output=0D
compared to a sine wave input - a good way to graphically see with a SPIC=
E=0D
transient analysis what is going on.=0D
=0D
PS: I am good with digital electronics, but I wish I was better at analog=
=0D
=2E..=0D
=0D
Rgs=0D
Ian.=0D
=0D
--=0D
http://www.piclist.com hint: To leave the PICList=0D
mailto:piclist-unsubscribe-request@mitvma.mit.edu

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