Page 200 - System on Package_ Miniaturization of the Entire System

174 Cha pte r F o u r

Device Commercial Balun LCP Balun
Frequency 4.8–5.9 GHz 4.8–5.9 GHz
Return loss (S ) (min) 16 dB −15.5 dB
11
Insertion loss (max) 0.6 dB 0.57 dB
Amplitude imbalance (max) 0.6 dB 0.33 dB
Phase imbalance (max) 5° 6°
Area 9 mm 2 5.16 mm 2

TABLE 4.4 Performance Comparisons of the Fabricated Balun

implementation compares to the commercially available balun with a 42 percent reduction
in size. In addition, the present balun can be embedded into the layers of LCP. Lumped-
element implementations using impedance matching networks have been proposed as a
means for size reduction [39]. As with any lumped-element approximation, this also
results in degradation in performance, particularly in amplitude imbalance across the
frequency bands. The lattice topology is a commonly used lumped-element solution for
implementing small-size narrow-band baluns, as shown in Figure 4.21. A combination of
low-pass and high-pass networks allows the splitting of the input signal into two output
signals that are equal in power but with a 180° phase difference. The low-pass and high-
pass networks can be implemented with as low a number as four passives (two inductors
and two capacitors), leading to small sizes (with the tradeoff of narrow-band operation).
The circuit topology also lends itself well to impedance transformation.
The design equations for the device are as follows:

Z = R source 1 ⋅ R load (4.7)
0
Z 1
L = 0 C = (4.8)
ω Z ω
0 0 0

C
Port 2
LL

Port 1

L

Port 3
C

FIGURE 4.21 Narrow-band balun topology with inductors and capacitors.