IAM-91563 Datasheet, PDF (8/14 Pages) Agilent(Hewlett-Packard) – 0.8-6 GHz 3V Downconverter

Application Guidelines
Several design considerations should be taken into ac-
count to ensure that maximum performance is obtained
from the IAM‑91563 downconverter. The RF and IF ports
must be impedance matched at their respective frequen-
cies to the circuits to which they are connected. This is
typically 50 ohms when the mixer is used as a building
block component 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 mis-
match 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 im-
age frequency and the IF filter prevents RF and LO signal
leakage into the IF signal processing circuitry.
RF
HP Filter
IF
LO
LP Filter
Figure 22. Image and IF Filters.
Additional design considerations relate to the use of high-
er bias current where greater linearity is required, bypass-
ing of the Source Bypass pin, bias injection, and DC block-
ing 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 especially important to maxi-
mize the conversion gain of the IAM-91563 mixer. Match-
ing 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 impedance of the RF
port is characterized by the measured reflection coeffi-
cients 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_RF²
(1)
For wireless bands in the 800 MHz to 6 GHz range, the
magnitude of the reflection coefficient of the RF port var-
ies 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 fre-
quencies 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 in-
stead. 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 combina-
tion 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, transmission lines, or a combina-
tion of both. The use of surface mount inductors and ca-
pacitors 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 networks 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 connected directly to a preceding stage
that has a voltage present, a DC blocking capacitor should
be used.
IF port
The IAM-91563 can be used for downconvesion to inter-
mediate frequencies in the 50 to 700 MHz range. Similar to
the RF port, the reflection coefficient at the IF is fairly high
and Equation 1 can be used to predict a mismatch gain
of up to 2.2 dB by impedance matching. A well matched
IF port will also provide the optimum output power and
LO-to-IF isolation. Reflection coefficients for the IF port are
shown in the Typical Reflection Coefficients Table.
The IF port impedance matching network should be of
the low pass filter type to reflect RF and LO power back
into the mixer while allowing the IF to pass through. The
shunt C, series L type of network in Figure 24 is a very
practical choice that will meet the low pass filter require-
ment while matching any IF impedances over the 50 - 700
MHz range to 50 ohms.
RF
IF
LO
IF
Output
Figure 24. IF Output LPF Matching.