Need opamp suggestion

Hi Mitesh,

Is your customer using the TLV2262A or the TLV2262C.  The A is a 950uV device and the other is a 2.5mA device.  Do they need precision with the new device?

Regards,

Tyler Noyes 

Hi Tyler,

Part numbers are TLV2262 not with "A"/ "C". - http://www.ti.com/product/TLV2262/samplebuy

Customer want to Lower IQ & lower noise device. They have made Instrumentation amplifier using TLV2262 at first stage with almost unity gain. Second stage is TLV2221 as difference amplifier with gain of 2. Third stage is again consists of dual TLV2221. Input signal is amplified with gain of 10, ultimate gain will be 20.

This signal is given to ADS1251, in last stage one of the opamp as buffer for 1.25V ref. (LMV431) to -ve input of ADC.

Customer is getting signal variation which shows ADC - count fluctuation even if input is not present. Tested with both input shorted to ground.

Noise performance is very critical at lower frequency, especially at 10Hz or even lower than that. TLV2262 is by far the best opamp I found at such lower frequency with lower IQ. Most of the opamp mentioning the lower noise but at 1kHz or 10KHz, when comes to low frequencies (around 10Hz or lower), then all these opamps are not even close to TLV2262.

We need suggestion which one is best suitable one for such application.

Mitesh

Hi Mitesh,

Based on your specs, I'm going to re-assign this question to the appropriate team. They will be able to help you.

Hi Mitesh,

What type of supply are you using for your amplifiers?  The parts you have mentioned have maximum supply voltage specifications of 8V and 10V.  But, if you can live with something that has a max supply voltage of 5.5V or 6V, that will open up some more options.

Also, have you considered the effect of op amp offset on your ADC?  I say this because the ADS1251 is a 24 bit ADC, which is fairly accurate.  Yet, the amplifiers in use could have a lower offset voltage.  Have you found that the offset of the discrete instrumentation amplifier is acceptable?

Regards,

Daniel Miller

Daniel,

This customer was assigned to me very recently & this opamp based design is older project. They are asking for the pindrop as a first choice, we can always recommend alternates way of implementation but first priority is to replace existing one or solve their issue on present one.

Supply for opamp is +/- 3.6V.  Pls. find TINA simulation file. for detailed understanding.  Actual issue is with Noise & ADC counts are keep fluctuating so their doubt is on opamp noise. 

As a alternate if we can come out with solution which has only one device & achieve the same functionality will reduce devices & noise. At this moment they are referring OPA196 & OPA187 as a replacement.

Mitesh

Circuit1.TSC

Hi Mitesh,

Sorry for the delay in response here and thanks for the further information.  Here's my advice.

1.  In the long-run, you may consider replacing this system, pr part of it, with a single INA.  This may simplify your design.  Given the age of the parts in use right now, I'm guessing that the existing design is quite a bit older and, perhaps, the design can be greatly simplified.  See here for the current selection.

2.  In the short term, I recommend you also open up another e2e thread in parallel with this one, if you haven't yet.  I'd post the thread with the ADC as the part in question and get the appropriate team to help you start figuring out what's going on with your system.  Have you only recently started having issues?  If that is the case, then it may not be an amplifier problem.  At any rate, they'll do a better job at debugging the ADC.

3.  In the meantime, I'm reaching out to the individuals that are most familiar with the types of parts you've requested.  Please allow me a bit of time to gather some alternatives.  I will have an update for you no later than sometime tomorrow.

4.  If you want to limit the total noise, an easy and effective solution is to cut out any unneeded bandwidth in your circuit.  This can be done with a simple low-pass filter.  It can also be done with a feedback capacitor, though this has more effect on your stability and is more effective for higher gain stages.

Regards,

Daniel

Hi Mitesh,

What do you think about the TLV2211?  It has better noise performance at low frequency and better current consumption.

Here's the TLV2211:

TLV2221:

If you need better performance, you might look into a low-power chopper amplifier.  Let me know what you think.

Regards,

Daniel

Hi Danile,

The TLV2211 seems to be a single supply opamp, whereas we need a dual supply part going upto at least +/- 3.6 Volts.