DC Bias
The provision of DC bias only occurs in a group of circuits that forms a single unit, such as an op-amp. Here the internal units or portions of the op-amp (like the input stage, voltage gain stage, and output stage) will be direct coupled and will also be used to set up the bias conditions inside the op-amp (the input stage will also supply the input bias to the voltage gain stage, for example). However when two op-amps are directly coupled the first op-amp will not supply any bias to the next - any DC at its output will form the input for the next. The resulting output of the second op-amp now represents an offset error if it is not the intended one.
Read more about this topic: Direct Coupling
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