Use ALL the pins?

Thread Starter

KLillie

Joined May 31, 2014
137
Just curious. I came across this trying to answer a post. If you had a dual op-amp, what what would be the harm in trying to use both instead of dealing with unused pins?
 

#12

Joined Nov 30, 2010
18,224
If you had two shoes, what would be the harm in wearing both of them?

Nobody said you have to unuse half of a dual op-amp and go buy another chip so you can use half of that one, too.
 
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Thread Starter

KLillie

Joined May 31, 2014
137
But see, if I'm told I gotta go through all the trouble of putting on my fake leg...I'm wearing that shoe!
 

#12

Joined Nov 30, 2010
18,224
I think that means you understood me.

The fact that there is a way to handle extra amplifiers if you don't need them doesn't mean you have to go buy too many amplifiers and not use some of them.
 

AnalogKid

Joined Aug 1, 2013
10,987
It really depends on the application. Because amplifier noise is uncorrelated even when two amps are on the same chip, there can be a noise advantage to having two amps in series, each with half the required circuit gain, compared to a single amplifier providing all of the gain. Generally speaking the two-amps-in-series also gets you wider bandwidth, which you can use to improve phase margin and high-frequency distortion.

ak
 

ErnieM

Joined Apr 24, 2011
8,377
Putting two op amps in parallel is a fine way to damage both devices.

Besides, there is way less hassle in dealing with unused pins then in not dealing with them.
 

crutschow

Joined Mar 14, 2008
34,285
It really depends on the application. Because amplifier noise is uncorrelated even when two amps are on the same chip, there can be a noise advantage to having two amps in series, each with half the required circuit gain, compared to a single amplifier providing all of the gain. .........................
For the same bandwidth, the noise of two op amps in series will always be larger than using a single amp, even if the two noises are uncorrelated (they add as their RSS sum).
But if the first op amp is configured to have significant gain, then the contribution from the second op amp can be made negligible.
 

Thread Starter

KLillie

Joined May 31, 2014
137
This was kind of my thought also AnalogK. Why not just use half as much gain and use both? I don't know maybe it was a silly question, but it sounds like using both "just because" could introduce more noise into the circuit?
 

WBahn

Joined Mar 31, 2012
29,979
Just curious. I came across this trying to answer a post. If you had a dual op-amp, what what would be the harm in trying to use both instead of dealing with unused pins?
In general, there isn't any harm -- that's why they put multiple amps in the same package.

There are some applications where two circuits can adversely interact when they contain opamps (or other devices) that share a piece of silicon, but by the time you are dealing with such applications you are usually dealing with a lot of other low-level and subtle issues, too.
 
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