IAM-91563 Datasheet, PDF (8/16 Pages) Agilent(Hewlett-Packard) – 0.8-6 GHz 3V Downconverter

materials at higher frequencies is
the degradation in the Q’s of
transmission lines used for
impedance matching.
Biasing
The IAM-91563 is a voltage-biased
device and is designed to operate
in the “normal mode” from a
single, +3 volt power supply with
a typical current drain of only
9␣ mA. The internal current regula-
tion circuit allows the mixer to be
operated with voltages as high as
+5␣ volts or as low as +1.5 volt.
The device current can be in-
creased up to 20 mA by adding an
external resistor from the Source
Bypass pin to ground. This feature
makes it possible to operate the
IAM-91563 in the “high power
mode” to achieve greater linearity.
Refer to the section titled “High
Linearity Mode” for information
on applications and performance
when using this feature.
Application Guidelines
Several design considerations
should be taken into account to
ensure that maximum perfor-
mance is obtained from the
IAM-91563 downconverter. The
RF and IF ports must be imped-
ance matched at their respective
frequencies to the circuits to
which they are connected. This is
typically 50 ohms when the mixer
is used as a building block compo-
nent in a 50-ohm system. These
ports have been left untuned on
the MMIC to allow the mixer to be
used over a wide range of RF and
IF bands. The LO port is already
sufficiently well matched (less
than 1 dB of mismatch loss) for
most applications.
As with most mixers, appropriate
filters must be placed at the RF
port and IF port such as in
Figure␣ 22. The filter in front of the
RF port eliminates interference
from the image frequency and the
IF filter prevents RF and LO signal
leakage into the IF signal process-
ing circuitry.
RF
IF
HP Filter
LO
LP Filter
Figure 22. Image and IF Filters.
Additional design considerations
relate to the use of higher bias
current where greater linearity is
required, bypassing of the Source
Bypass pin, bias injection, and DC
blocking and bypassing.
Each of these design factors will
be discussed in greater detail in
the following sections.
RF Port
A well matched RF port is espe-
cially important to maximize the
conversion gain of the IAM-91563
mixer. Matching is also necessary
to realize the specified noise
figure and RF-to-LO isolation. The
amount the conversion gain can
be increased by impedance
matching is equal to the mismatch
loss at the RF port. The imped-
ance of the RF port is character-
ized by the measured reflection
coefficients shown in Typical
Reflection Coefficients Table. The
maximum “mismatch gain” that
results from eliminating the
mismatch loss is expressed in dB
as a function of the reflection
coefficient as:
G_{RF, mm}
=
10
log₁₀
1–
1
Γ_RF
2
(1)
For wireless bands in the 800 MHz
to 6 GHz range, the magnitude of
the reflection coefficient of the RF
port varies from 0.91 to 0.80,
which corresponds to a mismatch
gain of 7.6 to 4.4 dB.
The impedance of the RF port is
capacitive, and for frequencies
from 800 MHz to 2.4 GHz, falls
very near the R=1 circle of a Smith
chart. While these impedances
could be easily matched to
50␣ ohms with a simple series
inductor, it is advantageous to use
a 2-element matching network of
the series C, shunt L type as
shown in Figure 23 instead. There
are two main reasons for this
choice. The first is to incorporate
a high pass filter characteristic
into the matching circuit. Second,
the series C, shunt L combination
will match the entire range of RF
port impedances to 50 Ω. Most
wireless communication bands
are sufficiently narrow that a
single (mid-band) frequency
approach to impedance matching
is adequate.
RF
Input ^C
RF
IF
L
LO
Figure 23. RF Input HPF Matching.
Impedance matching can be
accomplished with lumped
element components, transmis-
sion lines, or a combination of
both. The use of surface mount
inductors and capacitors is
convenient for lower frequencies
to minimize printed circuit board
space. The use of high impedance
transmission lines works well for
higher frequencies where lumped
element inductors may have
excessive parasitics and/or self-
resonances.
If other types of matching net-
works are used, it should be noted
that while the RF input terminal of
the IAM-91563 is at ground
potential, it should not be used as
a current sink. If the input is
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