Environmental Engineering Reference
In-Depth Information
Resistance is that found at node Z1-Y2, and is equal to
where is evaluated by short-circuiting node Z of transistor T2. Hence
from (2.11) it is equal to
which is usually a large resistance and can be neglected in (6.77).
Finally, we evaluate capacitors and The first capacitance is equal
to but, as already mentioned, it is redundant because of the
dominant contribution given by the compensation capacitor. The second
capacitance is equal to the load capacitance(usually much greater than the
intrinsic capacitances). This is an important contribution as it determines the
second pole. Once all the circuit parameters in Fig. 6.31 have been
identified, the compensation steps straightforwardly follow those given in
Chapter 5.
The compensation of a series-shunt feedback amplifier with an output
buffer is achieved in a substantially similar manner.
Observe that the approach described above is implicitly equivalent to the
one customarily used by circuit designers, that requires breaking the
feedback loop and suitably updating the impedance levels. This approach is
pictorially described in Fig. 6.33. It is also worth mentioning that analytical
methods like the one described in [T92] have been developed to find the
loop gain without breaking the loop. These techniques are particularly
efficient if associated with circuit simulation programs.
Search WWH ::




Custom Search