LV instrumentation amp with decent CM input range?

F

Frank Miles

Guest
I'm looking for an instrumentation amp to be run on a lithium battery (3V).
I need low power consumption and a common-mode input range (CMIR) of as much
of the "power supply" as I can get. All of the IAs I've looked at so far
- TI, AD, LT, good grief I've even checked out Maxim's - all are pretty
limited on CMIR. Especially towards the positive end. The closest, so far
is the AD623, but that's not good enough.

Have I overlooked something? Must I build my own from a RRIO amp + resistors?
I need to switch gains, so that's looking kinda klunky!

Any tips appreciated!

-f
 
I'm looking for an instrumentation amp to be run on a lithium battery (3V).
I need low power consumption and a common-mode input range (CMIR) of as much
of the "power supply" as I can get. All of the IAs I've looked at so far
- TI, AD, LT, good grief I've even checked out Maxim's - all are pretty
limited on CMIR. Especially towards the positive end. The closest, so far
is the AD623, but that's not good enough.

Have I overlooked something? Must I build my own from a RRIO amp + resistors?
I need to switch gains, so that's looking kinda klunky!
Click to expand...
You can boost the input range by running the input signal(s) through
a resistor divider to ground. Of course, you have to get the resistors
ballanced.


Here is another possibly crazy idea to add to your collection...

They make flying-cap boost regulators. The chip and caps might
be less-ugly than the do-it-yourself alternatives.

--
These are my opinions, not necessarily my employer's. I hate spam.
 
Hal Murray wrote:

I'm looking for an instrumentation amp to be run on a lithium battery (3V).
I need low power consumption and a common-mode input range (CMIR) of as much
of the "power supply" as I can get. All of the IAs I've looked at so far
- TI, AD, LT, good grief I've even checked out Maxim's - all are pretty
limited on CMIR. Especially towards the positive end. The closest, so far
is the AD623, but that's not good enough.

Have I overlooked something? Must I build my own from a RRIO amp + resistors?
I need to switch gains, so that's looking kinda klunky!


You can boost the input range by running the input signal(s) through
a resistor divider to ground. Of course, you have to get the resistors
ballanced.


Here is another possibly crazy idea to add to your collection...

They make flying-cap boost regulators. The chip and caps might
be less-ugly than the do-it-yourself alternatives.

Hmm:
Click to expand...
Flying-cap boost regulators? that's a new one on me.
do you mean charge pump maybe?


--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
 
On Wed, 21 Nov 2007, Hal Murray wrote:

I'm looking for an instrumentation amp to be run on a lithium battery (3V).
I need low power consumption and a common-mode input range (CMIR) of as much
of the "power supply" as I can get. All of the IAs I've looked at so far
- TI, AD, LT, good grief I've even checked out Maxim's - all are pretty
limited on CMIR. Especially towards the positive end. The closest, so far
is the AD623, but that's not good enough.

Have I overlooked something? Must I build my own from a RRIO amp + resistors?
I need to switch gains, so that's looking kinda klunky!

You can boost the input range by running the input signal(s) through
a resistor divider to ground. Of course, you have to get the resistors
ballanced.


Here is another possibly crazy idea to add to your collection...

They make flying-cap boost regulators. The chip and caps might
be less-ugly than the do-it-yourself alternatives.

--
These are my opinions, not necessarily my employer's. I hate spam.


Thanks, but... the differential signal is very low level. Can't attenuate
Click to expand...
without losing it in the noise. I'm also very space and power limited, so
it's hard to come up with a converter - and adequately filter its output
to keep supply-coupled noise in check.

I was really hoping someone would know of a device that wouldn't lose
half or more of its CMIR when operated at low voltages. If there's no
alternative, either the RRIO+resistors or sort of voltage converter may
be unavoidable.

Thanks for the thoughts...

-f
 
In article
<Pine.LNX.4.64.0711212122550.28359@homer21.u.washington.edu>,
Frank Miles <fpm@u.washington.edu> wrote:

I was really hoping someone would know of a device that wouldn't lose
half or more of its CMIR when operated at low voltages. If there's no
alternative, either the RRIO+resistors or sort of voltage converter may
be unavoidable.
Click to expand...
Two-three lithium batteries might be simpler than a voltage converter.

--
Cats, coffee, chocolate...vices to live by
 
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