Rainbow Electronics MAX19997A - Manual (Page 30)

MAX19997A
Dual, SiGe High-Linearity, 1800MHz to 2900MHz
Downconversion Mixer with LO Buffer
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The MAX19997A’s RF range can be further extended
down to 1800MHz by adding one additional tuning ele-
ment on each RF port. For 1950MHz RF applications,
connect a 12nH shunt inductor from pins 1 and 9 to
ground. Also, change the value of the DC-blocking
capacitors (C1 and C8) from 22pF to 1pF. See the
Typical Application Circuit for details.
LO Input, Buffer, and Balun
A two-stage internal LO buffer allows a wide input
power range for the LO drive. All guaranteed specifica-
tions are for an LO signal power from -3dBm to +3dBm.
The on-chip low-loss balun, along with an LO buffer,
drives the double-balanced mixer. All interfacing and
matching components from the LO input to the IF out-
puts are integrated on-chip.
High-Linearity Mixer
The core of the MAX19997A is a pair of double-
balanced, high-performance passive mixers.
Exceptional linearity is provided by the large LO swing
from the on-chip LO buffer. When combined with the
integrated IF amplifiers, the cascaded IIP3, 2RF-2LO
rejection, and NF performance are typically +24dBm
IIP3, -67dBc, and 10.3dB, respectively for low-side LO
injection architectures covering the 2300MHz to
2900MHz band. Cascaded performance levels are
comparable for high-side LO injection architectures;
IIP3, 2LO-2RF rejection, and NF levels are typically
rated at +24dBm IIP3, -73dBc, and 10.4dB, respective-
ly over the same 2300MHz to 2900MHz band.
Differential IF Output Amplifier
The MAX19997A mixers have an IF frequency range of
50MHz to 500MHz. The differential, open-collector IF
output ports require external pullup inductors to V
CC .
These pullup inductors are also used to resonate out the
parasitic shunt capacitance of the IC, PCB components,
and PCB to provide an optimized IF match at the fre-
quency of interest. Note that differential IF outputs are
ideal for providing enhanced 2RF-2LO and 2LO-2RF
rejection performance. Single-ended IF applications
require a 4:1 balun to transform the 200
Ω differential
output impedance to a 50
Ω single-ended output. After
the balun, voltage standing-wave ratio (VSWR) is typi-
cally 1.2:1.
Applications Information
Input and Output Matching
The RF and LO inputs are internally matched to 50
Ω. No
matching components are required for RF frequencies
ranging from 2400MHz to 2900MHz. RF and LO inputs
require only DC-blocking capacitors for interfacing.
If desired, the RF band can be extended down to
1800MHz by adding two external matching compo-
nents on each RF port. See the
Typical Application
Circuit and Table 2 for details.
The IF output impedance is 200
Ω (differential). For
evaluation, an external low-loss 4:1 (impedance ratio)
balun transforms this impedance down to a 50
Ω single-
ended output (see the Typical Application Circuit ).
Reduced-Power Mode
Each channel of the MAX19997A has two pins
(LO_ADJ_, IF_SET) that allow external resistors to set
the internal bias currents. Nominal values for these
resistors are shown in Tables 1 and 2. Larger-value
resistors can be used to reduce power dissipation at the
expense of some performance loss. If ±1% resistors are
not readily available, ±5% resistors may be substituted.
Significant reductions in power consumption can be
realized by operating the mixer with an optional supply
voltage of +3.3V. Doing so reduces the overall power
consumption by up to 53%. See the
+3.3V Supply AC
Electrical Characteristics table and the relevant +3.3V
curves in the Typical Operating Characteristics section
to evaluate the power vs. performance tradeoffs.
Layout Considerations
A properly designed PCB is an essential part of any
RF/microwave circuit. Keep RF signal lines as short as
possible to reduce losses, radiation, and inductance.
For the best performance, route the ground pin traces
directly to the exposed pad under the package.
The PCB exposed pad MUST be connected to the
ground plane of the PCB. It is suggested that multiple
vias be used to connect this pad to the lower-level
ground planes. This method provides a good RF/ther-
mal-conduction path for the device. Solder the exposed
pad on the bottom of the device package to the PCB.
The MAX19997A evaluation kit can be used as a refer-
ence for board layout. Gerber files are available upon
request at
www.maxim-ic.com .