OPA380: Designing with low impedance input signal

Hello Archie,

  Are you looking for a differential output signal or are you looking for a differential input? The bipolar electrode remark would suggest the latter, and this would be a varying current output electrode? If so, the OPA830 would not work as a differential input/amplification. The architecture is unique as to improve input offset voltage. 

  What are the input characteristics/range to the amplifier?

Thank you,
Sima 

Hi Archie,

please post a schematic or at least a block diagram.

Kai

Hi Experts,

Thanks for your responses. This is the information we have received from Cx:

There are two input signals that need to be differentially amplified into one output. The problem is that they are low input impedance signals. Is there another amplifier you would recommend?

Thank you.

Regards,
Archie A.

Hi Archie,

the problem is that from these two sentences I don't know what the customer is trying to do. And with this little information I'm not able to say anything useful.

Kai

Hello Archie,

  As Kai suggested, a block diagram would be helpful. 

  Here are two examples:

  Which is the correct interpretation? Also any design requirements the customer can share such as input signal characteristics and gain requirements would be helpful.

Thank you,

Sima 

Hi Sima,

Thanks for guiding.

Here are the design requirements provided:
- Suitable for a biomedical application (could be recommended in the application section to a data sheet for any biomedical example)
- Single channel
- High CMRR (+100)
- Differentially amplify two input signals
- Accept a low input impedance signal within the mV range.

Additional information from Cx:

Our group has explored solutions of adding front-end resistance and passing the signal through a differential amplifier (attempt to reduce the input current so that it can be accepted by a DiffAmp), or perhaps coupling a transimpedance and differential amplifier to achieve this. The major problem we are facing is due to the low input impedance of our signal.

We would like to use an amplifier from TI to speed our design process, but we are realizing we may need to consult someone to build it for us. If you have any existing TI amplifier recommendations it would be greatly appreciated.

Thank you again for your time

Regards,
Archie A.

Hello Archie,

   Thank you for gathering more information. Even when using a shunt resistor with an amplifier, the simplest method is the latter which is coupling a dual transimpedance amplifier to a differential amplifier. 

   If looking around the same GBW, I would recommend our new high precision and high CMRR amplifier, the OPA817. 

Thank you,
Sima