Environmental Engineering Reference
In-Depth Information
Equation (5.96) can be simplified by observing that for the auspicious
condition parameter is lower than 1/3 and for practical phase
margin values around 60°-70° we have
indicating that the zero can also be neglected when evaluating the phase
margin. In conclusion, (5.96) can be approximated by (5.82).
5.5.4 RHP Cancellation with One Real Current Buffer
As can be deduced by returning to Fig. 5.14, the overall feedback current
is given by the sum of the currents flowing into the two compensation
capacitors. Thus, we need to use only
one
current buffer in the loop to break
the forward path, as shown in Fig. 5.19, simplifying design and reducing
power and area consumption. Since the overall feedback current is still the
same, the loop-gain transfer function is again given by equation (5.80) and
(5.82) still holds.
If we consider the finite input resistance of the current follower,
the
loop gain will include another pole and two zeros, as shown below
in which the two zeros have a negative real part. Besides, they are real if
