Looking For: SMT Low Noise Precision Instrumentation Amp

[Jeff]

Hello,

Can anyone suggest a very low noise, precision instrumentation amplifier, in
a SMT package. Offset voltages don't matter much as long as they are
constant, and the temperature coefficient is very low. An AD625 would do the
job, but the SMT parts are rare, and very expensive (only available in Mil
spec). An industrial temp range is preferred.

Thanks,

 

[Jeff]

Hello,

Can anyone suggest a very low noise, precision instrumentation amplifier, in
a SMT package. Offset voltages don't matter much as long as they are
constant, and the temperature coefficient is very low. An AD625 would do the
job, but the SMT parts are rare, and very expensive (only available in Mil
spec). An industrial temp range is preferred.

Thanks,

Oh, since this is for a low level, slowly changing DC voltage, a high
bandwidth is not needed.

 

[John Larkin]

Hello,

Can anyone suggest a very low noise, precision instrumentation amplifier, in
a SMT package. Offset voltages don't matter much as long as they are
constant, and the temperature coefficient is very low. An AD625 would do the
job, but the SMT parts are rare, and very expensive (only available in Mil
spec). An industrial temp range is preferred.

Thanks,

The TI/Burr-Brown INA-series parts are nice.

John

 

[CFoley1064]

Can anyone suggest a very low noise, precision instrumentation amplifier,

in

Oh, since this is for a low level, slowly changing DC voltage, a high
bandwidth is not needed.

Your initial choice of an AD625 indicates you want some pretty good specs. You
might want to take a look at the LT1167AIS8, available from DigiKey at $12.75
USD in stock. It's surface mount, has an industrial temp range (-40C to 85C),
and has specs comparable to the AD Rolls Royce at a better price.

Good luck, and have fun.
Chris

 

[Jeff]

Your initial choice of an AD625 indicates you want some pretty good specs.

I'm measuring a slowly changing DC signal with a peak to peak voltage change
that is typically in the order of 20 to 40 uV, with a resolution of about
1/100 to 1/1,000 of that. The good thing is that the drift stability of the
system has to only last a few minutes. I'm trying to build the amplifier as
close as possible to the signal source to help reduce noise, and simplify
the system down the line (i.e. avoiding stray thermocouples everywhere and
allowing the use of electrical plugs). The signal is from a isothermal
reference thermocouple closely connected to a thermocouple stuffed inside a
0.8 mm outer diameter stainless steel hermetic tube along with two other
wires, forming a special sensor that under some conditions will only change
about 0.5 to 1 degree, in which this temperature change must be accurately
recorded.

Looking at some of Liner Tech's data sheets, it looks as if the LTC1100
chopper stabilized amp might just be the IC I am after, even though I do not
need the absolute DC accuracy an chopper amplifier has to offer. Maxim IC,
however, has some decent instrumentation amps in a SOT23-6 package that
could be worked into the sensor quite nicely. Now looking back at Linear
Tech they offer the chopper stabilized LTC2050 in SOT23, which has even
better noise specs then the Maxim parts!

You
might want to take a look at the LT1167AIS8, available from DigiKey at $12.75
USD in stock.

Not bad -and it did help me find the LTC1100, and the LTC2050. I'll decide
which one (or both) to try after I get a few hours of sleep.

 

[Jeff]

The TI/Burr-Brown INA-series parts are nice.

Yes, they do have some very nice parts! Decent pricing too.

I think I will settle on a Linear Tech LTC1100, or a LTC2050 (OP Amp) due to
its tiny SOT23 size, along with a couple of precision resistors.