instrumentation amplifier

Hi Chirag,

Chirag Panchal2 said:

I would be grateful if you could suggest an instrumentation amplifier/s (I would like to keep unity gain).

You are correct. I do not see anything special about LT6012CS opamp. It is costly to build an instrumentation amplifier (IA) with discrete components, especially you have to use matching and precision resistors to increase CMRR ability. The integrated IA is definitely a way to go.

Could you share with us the IA's application and design requirements?

Based on the LT6012CS datasheet, it has BW approx. 350kHz, 134uA/Ch quiescent current, max. Vos is 60uV and low Ib current approx. 300pA. 

TI has a very wide selection options of precision IA that will meet above specification. For unity gain IA, you do not have to populate Rg or the gain resistor. You may leave it open (Rg is infinitive) and Gain will be 1 or unity for the IA application. Two random examples are shown below and there are many more that can be found in the link below. 

https://www.ti.com/amplifier-circuit/instrumentation/overview.html?keyMatch=INSTRUMENTATION%20AMPLIFIER

If you have any questions, please let us know. 

Best,

Raymond

Application: measure AC grid voltage, DC battery voltage and current using AMC1301DWVR. We get differential output (VPCCC-P and VPCCC-N) from the AMC 1301 and fed into LT6012cs to get single output. The single output is connected to our processor TMS320F28377. Would you be able to suggest more than one IA?

If you require any more information, please do not hesitate to contact me.

Thanks, and regards,

Chirag

Hi Chirag,

have you tested whether there's an improvement when using an instrumentation amplifier at the output of AMC1301 instead of the standard differential amplifier?

Kai

Hi Kai,

No I haven't tested yet. That was the reason I contacted TI to help me to select a few of them so I can try them to check the performance. In our case, if we get similar performance like LT6012CS, we would be happy as my main concept is to reduce the cost. in our design we are using around 8 of them plus precision resistors . 

Thanks 

Hi Chirag,

Kai has a good point. THP210 a precision full differential amplifier may replace LT6012CS constructed instrumentation amplifier (~140dB CMRR & PSRR + other high performance spec.). THP210 is an ultra-low offset, low noise FDA with single supply operating range from 3 to 36Vdc. It is a possibility. It is lower in cost vs. LT6012CS. 

Regarding to the selection of instrumentation amplifiers, it seems that you are interested in low and single operating supply voltage IA, say 3.3V or 5.5Vdc. What is the input common mode, Vcm for the input range for IA? I provided some IA suggestions below based on the low single supply voltage criteria. For instance, INA823 and INA826 may work for you. If INA333 or INA317's performance is comparable to the existing LT6012CS discrete constructed IA, then we may have a lot more low voltage options (including cost estimation). 

 LT6012CS has high CMRR and PSRR as op amp specification, but when a discrete IA is constructed using the op amps, the overall CMRR characteristics are all changed (including the noise specification). So it is not apple to apple comparisons vs. IAs' datasheet. If we have a reference IA part vs. the discrete IA, then we will know what are the best options and lower costs. Of course, we can figure this out by doing simulation as well (will need more design requirements).  

https://www.ti.com/amplifier-circuit/instrumentation/products.html#p358min=1.8;5.5&p480=1&p1181typ=0.001;2&sort=p4min;desc

If you have additional questions, please let us know. 

Best,

Raymond