Page 248 - System on Package_ Miniaturization of the Entire System

222 Cha pte r F o u r

Mkr1 5.10 GHz
Ref 0 dBm Atten 10 dB –12.21 dBm
Samp
log 1
10 dB/
System alignments, align now, all required

2
Marker
5.1 GHz
–12.21 dBm

Center 13.25 GHz VBH 3 MHz Span 26.5 GHz
Res BH 3 MHz Sweep 265 ms
FIGURE 4.69 Spectrum of the TVCO with the type 2 transformer design. The f 0 shifted to 5.1 GHz
from the design frequency of 1.9 GHz.

capacitors C and C . In both the transformer types, C is the capacitance
1 m 1
connected across inductance L that adds a transmission zero for harmonic
1
rejection. From the results it can be observed that at nonharmonic frequencies
(4.95 GHz) there is considerable current at the output terminal (C ) that can
m
cause a significant shift in the magnitude of the loop gain and phase shift
around the loop. Figure 4.69 shows the measured spectrum of the TVCO with
the type 2 transformer. The fundamental frequency has shifted to 5.1 GHz from
the design frequency of 1.9 GHz.

4.6.2 Digital-to-Analog Coupling
Noise coupling through the power supply is a difficult problem to solve, primarily
because of the physical connection that it provides between the RF and digital
subdomains. Ideally, the RF subdomain should be separated from the digital circuitry
such that there exists no coupling between them. As the frequencies of operation
increase, however, electromagnetic coupling becomes important and it becomes
impossible to completely isolate any two regions of the system.
As frequencies increase, power and ground planes are required to support a low-
inductance power delivery system. Though the planes have low-inductance properties
at high frequencies, they also couple energy, especially at their resonant frequencies.
Several techniques have been applied to solve this isolation problem. The classical
method is to use split planes. If a dc connection is required, the split planes can be
connected using a low-pass functional block. This requires additional components and
provides only marginal isolation. A very promising method for isolation is based on