[AmpeROSE] The amplification

As you saw in our previous posts, we were going to use the amplifier MAX4239 but after some simulations, we decided to replace it with the ADA4807. We will explain here why we took this decision.

To test the amplifier, we did a simulation using them in the same way they will be used in AmpeROSE: as a differential amplifier with a gain of 100. Here is the schematic of this simulation.

As you can see, we put the same signal as input on the two differential amplifiers, this signal is represented on the following figure.

It is a simple pulse, we put this signal because we think it represents well the activation of a peripheral that consumes a lot after the system was in sleep mode. When we tried such an input on our simulation with the MAX4239, we got a really bad surprise that you can see on the following picture:

The amplifier did not react fast enough because it has a slew rate too low! After that we decided that we have to change it because a common case like this one should be measured well.

So we searched for others operational amplifiers with a better slew rate and we finally choose to use the ADA4807 which was much better as you can see on the output on the figure below.

You know now why we change our amplifier. This choice has unfortunately some drawbacks, notably we will need here a negative supply. This amplifier also has bigger offset but since the software will correct it with the initial calibration, this is not a problem.

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