INA828: Exceeding 1000 Gain Specification

Hi Musa,

have you seen in datasheet that the bandwidth of INA828 is decreasing when the gain is increased? Can you live with that? What is the bandwidth of your application?

Kai

The application is EEG. The signal bandwidth is pretty low, the sampling rate of my ADC is 250 Hz.
Based on the numbers' trend, I'd assume I'd be pretty safe above 1000 within reason. However, I want to make sure there are no other issues.
If bandwidth is the only issue then I think I should be fine at around 5-10kV/V.

Thank you,

Musa

Hi Musa,

INAs are certainly capable of operating in gains higher than that specified in the datasheet. The datasheet specification serves as the maximum gain for which we guarantee you will see the performance given in other specs. Exceeding the 1000 V/V limit will for example lead to increased gain error and non-linearity past the maximum limits we give.

It can be very difficult to work with gains in the 5-10kV/V range because any noise in your system also sees this gain, not to mention the offset voltage and bias current error may start to eat up a significant portion of your output range. You should take care to make sure any noise on the inputs comes in as common-mode. Additionally if you are interfacing with a BNC cable then you will want to drive the shield to the same common-mode potential as your input to minimize leakage currents.

Hi Musa,

stray capacitance from output to input can make your amplifier become unstable if the gain is extremely high. This can be problematic with the cabling of your EEG application. So, filter caps from both inputs to signal ground seem to be advisable. And shielding of the gain setting resistor from the output wiring could be helpful.

Another reason for not to increase the gain too much is that the precision of the INA would suffer. But this seems not to be an issue in your EEG application.

Kai