IAM-91563 Datasheet, PDF (9/16 Pages) Agilent(Hewlett-Packard) – 0.8-6 GHz 3V Downconverter

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 intermediate
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 match-
ing. 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 requirement 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.
The DC bias is also applied to the
mixer through the IF port. Figure
25 shows how an inductor (RFC)
is used to isolate the IF from the
DC supply. The bias line is by-
passed to ground with a capacitor
to keep RF off of the DC supply
lines and to prevent dips or peaks
in the response of the mixer.
Bypass
Capacitor
V_d
RFC
RF
IF
IF
Output
LO
Figure 25. Bias Connection.
LO Port
The LO input port is internally
matched to 50 Ω within a 2.2:1
VSWR over the entire operating
frequency range. Additional
matching will normally not be
needed. However, if desired, a
small series inductor can be used
to provide some improvement in
the LO match and thus reduce the
LO drive level requirement by up
to 0.7 dB. Reflection coefficients
for the LO port are shown in the
table of Typical Reflection
Coefficients.
Source Bypass Pin
The Source Bypass pin should be
RF bypassed to ground at both the
RF and LO frequencies as well as
the IF. Many capacitors with
values large enough to adequately
bypass lower intermediate fre-
quencies contain parasitics that
may have resonances in the RF
band. It is often practical to use
two capacitors in parallel for this
purpose instead of one. A small
value, high quality capacitor is
used to bypass the RF/LO frequen-
cies and a large value capacitor
for the IF. When biased in the high
linearity mode, a resistor is added
from the Source Bypass pin to
ground.
High Linearity Mode
The IAM-91563 has a feature that
allows the user to place an
external resistor from the Source
Bypass pin to ground and increase
the device current from a nominal
9 mA to as high as 20 mA. The
additional current increases mixer
linearity (IP3) and output
power(P1dB). Mixer performance
at higher device current is shown
in Figures 26 and 27.
14
12
NF
10
8
GAIN
6
4
7 9 11 13 15 17 19
DEVICE CURRENT (mA)
1000 56 21 9 5 3
Approximate Resistor Value (Ω)
Figure 26. Available Conversion Gain
Figure 26. Available Conversion Gain
and SSB Noise Figure vs. Device
Current (Source Resistor).
0
-2
IP₃
-4
P_{1 dB}
-6
-8
-10
7 9 11 13 15 17 19
DEVICE CURRENT (mA)
1000 56 21 9 5 3
Approximate Resistor Value (Ω)
Figure 27. One dB Compression and
Input Third Order Intercept Point vs.
Device Current (Resistor).
As an example of improved
linearity, the use of a 15 Ω resistor
at the Source Bypass pin increases
the device current to 14 mA. At
1.9␣ GHz, the input IP ₃ is increased
from -6.5 dBm to -3 dBm. Increas-
ing the LO drive level from -5 dBm
to -1 dBm further increases the
input IP₃ to 0 dBm.
7-143