Environmental Engineering Reference
In-Depth Information
Generally the output capacitance,
is much higher than the inner
capacitance,
and relationship (5.38) can be further
simplified
to
Hence, for a given phase margin, the required compensation capacitance is
slightly lower than the value required by the optimised compensation with
voltage buffer in (5.34), while the resulting gain bandwidth product is
slightly
higher.
However, compensation with a real current buffer (and specifically, with
finite input resistance) is not as straightforward as the other compensation
approaches. As shown in reference [PP97], to achieve compensation we
have to guarantee that the input resistance of the current buffer,
is equal to
or lower than half
Moreover, the condition
represents an optimum to maximise the gain-bandwidth product. Under
condition (5.40) the required compensation capacitor is
where
Usually, relationship (5.41) can be further approximated
