LTSpice -- I'm trying to design an instrumentation amplifier for an EMG.

Thread Starter

Lexcoim

Joined Oct 26, 2023
1
First, thank you for your attention. I'm trying to design an instrumentation amplifier for an EMG, supposedly, the one I'm trying to make has a gain of 41. I'm not that adept with spice design and I've been trying to get a cohesive results with I'm expecting, but I'm getting a gain of 10, but I think it is a default declaration from the program. Could someone lead me into the correct path? Any input is appreciated.

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michael8

Joined Jan 11, 2015
407
U1 and U2 need power from a & b, not gnd. You need to be sure that the inputs and outputs stay within the allowed
range (see common mode range and output ranges on the datasheet) For the LM741 I'd guess/remember
that you can't get very close to the V+ or V- power supply rails values for either input or output.

Figure staying 2 volts away -> with +9 -9 that means all the inputs need to be within +7 to -7 volts.

Clearly U1 with c at near ground is to close to the U1 negative supply which is ground.
 

eetech00

Joined Jun 8, 2013
3,820
First, thank you for your attention. I'm trying to design an instrumentation amplifier for an EMG, supposedly, the one I'm trying to make has a gain of 41. I'm not that adept with spice design and I've been trying to get a cohesive results with I'm expecting, but I'm getting a gain of 10, but I think it is a default declaration from the program. Could someone lead me into the correct path? Any input is appreciated.

View attachment 305953
Why not use a real instrumentation amplifier chip?
 

crutschow

Joined Mar 14, 2008
34,047
I second eetech00"s suggestion.
An IC instrumentation amp will have greatly superior performance as compared to a roll-your-own design, primarily because of much better matching of the resistor values.
 
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