AD8628: Signal sourcing

Q

Reading the 8628 data sheet I don't see the simplified block diagram of the
amplifier. The question is the following: when looking to the signal source
trough AD8628 is that mean that 8628 connected to the signal source only half
the overall time (another half of time used to zeroing)? In another words -
with the unity gain the signal-to-noise ratio remains the same at the output as
one at the input of 8628? (Say in the 0-8 kHz bandwidth).

A

My answer is that the signal source driving the input pins of the AD8628 will
always be connected to the amplifier. The switching mechanism (auto-zero)
occurs only on the internal nulling amplifier (the AD8628 has two amplifiers:
the main amplifier and the nulling amplifier). Please read sections: “Basic
Auto-Zero Amplifier Theory”, “Auto-Zero Phase”, and “Amplification Phase” of
the AD8571/AD8572/AD8574 Data Sheet, pages 14, 15, and 16. This is an
excellent source of information concerning the theory behind our auto-zero
amplifiers.