CMOS Optical Preamplifier Design Using Graphical Circuit Analysis

that
and the port impedance is given by
Z port
i p
4.4 Determining Port Impedances 94
(4.13)
(4.14)
Equation (4.14) is in fact an alternative representation of Blackman’s Impedance
Formula. To recognize this, we need to determine the physical significance of the
terms L2 and (L1 + L2 ). Because w is a controlled source, it is possible to split node
w into separate source and sink nodes, wsource and wsink as shown in Figure 4.18.
The loop transmittance, L, is equal to the ratio, wsink ⁄ wsource, which is simply the
negative of the return ratio that is referenced to the controlled source, w
. From
Figure 4.17, we can see that
≡
v p
----
i p
P 1
=
Z°
∆1 = 1 – L2 ∆ = 1 – ( L1 + L2) i SCp v p
P1∆1 1 – L2 = ------------ = Z° ----------------------------------
∆ 1 – ( L1 + L2) Z o
T wp
Tpx
Figure 4.17 Alternative SFG for the feedback amplifier.
L 1
x
T wx
L 2
L L
w
Figure 4.18 Splitting node w.
T w
k
w
wsink wsource