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_Cheap_ Instrumentation Amplifier?

A

Anonymous Coward

Jan 1, 1970
0
I am looking for a low-performance unity gain instrumentation
amplifier to replace an "opamp & 4ea 1% resistors" circuit.
It doesn't have to be very good - it ends up feeding an
8-bit ADC - and it doesn't have to be very fast - the signal
is 60 Hz 3.5 VAC with <0.2V of common mode to be rejected.
What is important is minimum board space (I have to fit a lot
of them into a small space) and a cost that is no more than
three or four times what the opamp and four 1% resistors costs.

Does anyone have a favorite part that fits the above description?
 
D

Don Bowey

Jan 1, 1970
0
I am looking for a low-performance unity gain instrumentation
amplifier to replace an "opamp & 4ea 1% resistors" circuit.
It doesn't have to be very good - it ends up feeding an
8-bit ADC - and it doesn't have to be very fast - the signal
is 60 Hz 3.5 VAC with <0.2V of common mode to be rejected.
What is important is minimum board space (I have to fit a lot
of them into a small space) and a cost that is no more than
three or four times what the opamp and four 1% resistors costs.

Does anyone have a favorite part that fits the above description?

As I recall, National recently came out with an Op Amp that had the
resistors included on the chip, for several gain options including zero.

Don
 
M

martin griffith

Jan 1, 1970
0
I am looking for a low-performance unity gain instrumentation
amplifier to replace an "opamp & 4ea 1% resistors" circuit.
It doesn't have to be very good - it ends up feeding an
8-bit ADC - and it doesn't have to be very fast - the signal
is 60 Hz 3.5 VAC with <0.2V of common mode to be rejected.
What is important is minimum board space (I have to fit a lot
of them into a small space) and a cost that is no more than
three or four times what the opamp and four 1% resistors costs.

Does anyone have a favorite part that fits the above description?
not exactly a inst amp, but INA2134 from TI might be worth
investigating, 8 pin dip, Zin is a bit low, o/p offset a bit high,
cmrr good
http://focus.ti.com/docs/prod/folders/print/ina2134.html

but 4R's and an opamp is still the cheapest


martin
 
S

Spehro Pefhany

Jan 1, 1970
0
As I recall, National recently came out with an Op Amp that had the
resistors included on the chip, for several gain options including zero.

Don

I don't think I've seen one for less than a dollar. In the $1-$2 range
in 1K, there are plenty of them, depending on what you want to do
about gain setting etc. Try a parametric search at AD & National.
This brand new one at a very reasonable $1.30/1K looks pretty cool:

http://www.analog.com/UploadedFiles/Data_Sheets/57089870037976AD8553_0.pdf

Insanely gross overkill for your application, but so what? Maybe you
can cut corners on some of those external parts.


Best regards,
Spehro Pefhany
 
D

David L. Jones

Jan 1, 1970
0
Anonymous said:
I am looking for a low-performance unity gain instrumentation
amplifier to replace an "opamp & 4ea 1% resistors" circuit.
It doesn't have to be very good - it ends up feeding an
8-bit ADC - and it doesn't have to be very fast - the signal
is 60 Hz 3.5 VAC with <0.2V of common mode to be rejected.
What is important is minimum board space (I have to fit a lot
of them into a small space) and a cost that is no more than
three or four times what the opamp and four 1% resistors costs.

Does anyone have a favorite part that fits the above description?

My first option is the AD620 if performance matters, or the cheaper and
lesser speced AD623 for general purpose jobs. No resistor required for
unity gain.
They may not be "low spec" enough for you though, so might blow your
budget. About $3.50ea in one-off qty at digikey for the AD623

Dave :)
 
W

Winfield Hill

Jan 1, 1970
0
Spehro Pefhany wrote...
I don't think I've seen one for less than a dollar. In the $1-$2 range
in 1K, there are plenty of them, depending on what you want to do
about gain setting etc. Try a parametric search at AD & National.
This brand new one at a very reasonable $1.30/1K looks pretty cool:

http://www.analog.com/UploadedFiles/Data_Sheets/57089870037976AD8553_0.pdf

I like the way Analog doesn't lock the datasheets. For example, I
was able to add your price as a comment. And they have a mistake
in the gain formula in the figure on page 13, so I simply used the
"Touch-Up Text" tool and fixed and saved it! Very satisfying.
 
J

John B

Jan 1, 1970
0
I am looking for a low-performance unity gain instrumentation
amplifier to replace an "opamp & 4ea 1% resistors" circuit.
It doesn't have to be very good - it ends up feeding an
8-bit ADC - and it doesn't have to be very fast - the signal
is 60 Hz 3.5 VAC with <0.2V of common mode to be rejected.
What is important is minimum board space (I have to fit a lot
of them into a small space) and a cost that is no more than
three or four times what the opamp and four 1% resistors costs.

Does anyone have a favorite part that fits the above description?

The Analog Devices AMP04 is one I have used in large numbers. It needs
a single resistor for gain control.
 
Anonymous said:
I am looking for a low-performance unity gain instrumentation
amplifier to replace an "opamp & 4ea 1% resistors" circuit.
It doesn't have to be very good - it ends up feeding an
8-bit ADC - and it doesn't have to be very fast - the signal
is 60 Hz 3.5 VAC with <0.2V of common mode to be rejected.
What is important is minimum board space (I have to fit a lot
of them into a small space) and a cost that is no more than
three or four times what the opamp and four 1% resistors costs.

Does anyone have a favorite part that fits the above description?

Your modest requirements, and R-paks -- cheap, small, and often
ratiometrically pretty good -- might make for a marraige of
convenience, if not ultimate beauty?

Regards,
James Arthur
 
Your modest requirements, and R-paks -- cheap, small, and often
ratiometrically pretty good -- might make for a marraige of
.....................................................................
marriage, gosh darn it.

James
"Typos shall not be revealed until akready[sic] posted." -- Cosmic
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