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AC coupling signal can isolate the DC signal from previous chip.
and you can build your own DC signal in your chip.
But it may loss some information especially when the informations are located nearby the low frequency.
DC coupling signal will not loss any informations. But usually it is hard to handle the DC drift problem especially when you want to amplify the input signal.
You should be able to tell the frequency range of the signal. Usually DC signals are from sensors that measure static values, such as solar light level or pH. Or such things as monitoring a battery voltage.
AC coupled amplifiers do not have much problem with bias drift because each stage is capacitivly or transformer coupled to the stages next to it. This was commonly done in the old days with valves/tubes. In integrated form the amplifiers are DC coupled and differential because you cannot economically make large value capacitors or transformers in silicon.
The signal which frequency is zero is called DC signal. If the signal frequency is different from zero, that's rest of all, it is the ac signal.
In multistage amplifiers, every stage has a dc bias. By using ac coupling, the stages prevents their own dc biases. So, only ac signals will be amplified.
If we want to amplify the DC+AC signals together, We must use dc coupling. Dc coupling can disturbs the dc biases, and we use carefully the DC coupling.
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