ABSTRACT
In two-port synthesis, specifications are often given in terms of the transfer functions such as the transfer voltage ratio, transfer current ratio, transfer impedance, or transfer admittance. The actual realization, however, is accomplished by means of the y-or z-parameters. Figure 8.1 shows a two-port network driven by a voltage source with output terminating in an impedance Z2(s). It is straightforward to show that the transfer voltage ratio function G12(s) can be expressed in terms of its y-parameters yij(s) or z-parameters zij(s) by the equation
G12(s) ¼ V2V1 ¼ y21
y22 þ Y2 (8:1)
where Y2(s)¼ 1=Z2(s). When the output is open-circuited, Equation 8.1 becomes
G12(s) ¼ V2V1 ¼ y21 y22
¼ z21 z11
(8:2)
Likewise, the transfer current ratio a12(s) can be expressed as
a12(s) ¼ I2I1 ¼ z21
z22 þ Z2 (8:3)
The zeros of transmission of a two-port network are defined as the frequencies at which the two-port results in zero output for a finite input. They play an important role in ladder development. There are many ways of producing zeros of transmission. One possibility to prevent the input signal from reaching the output is by shorting together all transmission paths or by opening all transmission paths by means of a series or parallel resonance. Another possibility is that signals transmitted by different paths cancel at the output.
