I am doing my design calculations for my project. I am considering using the following chip
Its a 32 channel chip. The data sheet discusses how to use this chip with AD7980 on page 26. I am confused about the following issue
The amplifier has a fixed gain of 200 and the EEG signal range is from 1uV to 100uV . So, the "MUX_out" pin will have 1uV x 200 = 200uV and 100uV x 200 = 20mV.
The used reference voltage is 2.5 volts. The ADC input voltage range is set from 0 to 2.5 Volts but the input signal ranges from 200uV to 20mV. The resolution of the ADC is 16 bits. 2.5 / 65536 = 38uV/ LSB.
The input signal is not utilizing the full range of the ADC and the amplifier does not have more than 200 gain. It might reduce the accuracy. Should I use reference voltage like 1 Volt instead of 2.5V?
But why the data sheet is using 2.5V reference voltage?
Plus the rms noise of the amplifier is 2uV rms (12uV peak to peak). How can I take this into my calculations?