INA-12063-TR1 Agilent(Hewlett-Packard), INA-12063-TR1 Datasheet - Page 10

• Manufacturer Part Number: INA-12063-TR1
• Description: 1.5 GHz Low Noise Self-Biased Transistor Amplifier
• Manufacturer: Agilent(Hewlett-Packard)

sponding increase in P
-5.2 dBm to +4.6 dBm. The data
sheet curve in Figure 8 character-
izes the P
Impedance Match – While it is
not a parameter per se, the
degree of difficulty of impedance
match may also be a consider-
ation in the selection of bias
current. Generally, the higher the
device current, the less “severe”
the impedance match, i.e.,
Step 3. Selection of PCB
Material
If the selection of PCB material
has not been preordained by
other factors (e.g., system stan-
dards) then it should be chosen at
this stage of the design process.
The printed circuit board material
is chosen at this step since it will
have an effect on the next step of
the stability analysis and on the
subsequent design of the imped-
ance matching networks.
Key factors to consider in the
selection of board material are
dielectric constant, RF loss
characteristics, board thickness,
and cost.
The dielectric constant and board
thickness together contribute to
the physical geometry of the
circuit, an important consider-
ation for miniaturization. Higher
dielectric constant material
enables the construction of more
compact circuits since the
physical dimensions of transmis-
sion lines are smaller.
In addition to transmission line
widths, PCB board thickness also
influences the quality of ground
vias. Ground vias in excessively
thick PCBs result in high induc-
tance paths to ground. For some
active devices, poor grounding
ms
,
ml
are all closer to 50 .
1dB
- I
c
tradeoff.
1dB
of
opt
,
can result in performance degra-
dation or reduced stability.
Dielectric loss is not a significant
factor for the moderate frequency
ranges over which the INA-12063
is normally used. Low loss, low
dielectric constant “microwave”
type materials are usually
reserved for applications
demanding the very lowest noise
figures (minimum circuit loss)
and/or for frequencies above
2 GHz.
An overall good choice for most
low cost wireless applications
using devices such as the
INA-12063 is a fiberglass-epoxy
material such as FR-4 or G-10
with a thickness in the range of
0.020 to 0.031 inches.
Step 4. Stability Analysis
A stability analysis is the next
step in the design process. The
purpose of this step is to examine
the circuit’s tendency to oscillate.
A linear CAD program, such as
Hewlett-Packard’s Touchstone
should be used to calculate the
stability factor, K, and stability
measure, B1. The factors K and
B1 are both derived from the
S-parameters for the INA-12063 at
the previously established bias
voltage and current. The condi-
tions for unconditional stability
are:
While a simple analysis based
only on the S-parameters is often
adequate at this point, a slightly
more rigorous analysis is recom-
mended that includes the para-
sitic elements in the device’s path
to ground. At this stage in the
design, a reasonable estimation
(guess) of this electrical path and
the construction of the ground
vias are adequate. For the
INA-12063, bear in mind that
K > 1 and B1 > 0
6-125
Pin 5 of the package is the critical
connection for “RF” grounding. A
typical RF path to ground con-
sists of a short length of transmis-
sion line terminated in one or
more ground vias. (The length of
the PCB pad between the
INA-12063 ground pin and the
ground should be modeled as a
microstripline (“MLIN” in Touch-
stone), and the plated through
ground holes as “VIA” elements.)
When evaluating stability, it is a
good practice to calculate K and
B1 over the full frequency range
for which S-parameters are
available. The reason for this is
that even though K and B1 may
indicate stability over the fre-
quency band of interest, the
possibility exists for a circuit to
oscillate at frequencies that are
far outside of the band of interest.
While unconditional stability
requires a positive, non-zero
value of B1, most of the following
stability analysis will focus on the
K factor since the value of K
indicates the degree of stability.
What should the minimum value
of K be to ensure stability? While
K=1.001 is stable, some margin is
prudent to allow for component
tolerances, temperature effects,
and manufacturing variations.
Typical rules of thumb suggest
that K should be at least 1.2 to
1.5.
There are three possible cases
resulting from the CAD analysis:
• Case 1 – K>1 over the entire
• Case 2 – K>1 within the band
• Case 3 – K<1 within the band
frequency range.
of interest and K<1 for some
frequencies outside of the
band of interest.
of interest.