SiGe High-Linearity, 815MHz to 995MHz
Downconversion Mixer with LO Buffer/Switch
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 inputs to the IF out-
puts are integrated on-chip.
optimize the performance for a particular frequency
band. Since approximately 140mA flows through this
inductor, it is important to use a low-DCR wire-wound coil.
If the LO-to-IF and RF-to-IF leakage are not critical
parameters, the inductor can be replaced by a short
circuit to ground.
Layout Considerations
A properly designed PC board is an essential part of
any RF/microwave circuit. Keep RF signal lines as short
as possible to reduce losses, radiation, and induc-
tance. For the best performance, route the ground pin
traces directly to the exposed pad under the package.
The PC board exposed pad MUST be connected to the
ground plane of the PC board. It is suggested that mul-
tiple 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 PC
board. The MAX9986 Evaluation Kit can be used as a
reference for board layout. Gerber files are available
upon request at www.maxim-ic.com.
High-Linearity Mixer
The core of the MAX9986 is a double-balanced, high-
performance passive mixer. Exceptional linearity is pro-
vided by the large LO swing from the on-chip LO
buffer. When combined with the integrated IF ampli-
fiers, the cascaded IIP3, 2LO-2RF rejection, and NF
performance is typically 23.6dBm, 67dBc, and 9.3dB,
respectively.
Differential IF Output Amplifier
The MAX9986 mixer has a 50MHz to 250MHz IF fre-
quency range. The differential, open-collector IF output
ports require external pullup inductors to V . Note that
CC
these differential outputs are ideal for providing
enhanced 2LO-2RF rejection performance. Single-
ended IF applications require a 4:1 balun to transform
the 200Ω differential output impedance to a 50Ω single-
ended output.
Power-Supply Bypassing
Proper voltage-supply bypassing is essential for high-
frequency circuit stability. Bypass each V
pin and
CC
TAP with the capacitors shown in the Typical Application
Circuit; see Table 1. Place the TAP bypass capacitor to
ground within 100 mils of the TAP pin.
Applications Information
Input and Output Matching
The RF and LO inputs are internally matched to 50Ω. No
matching components are required. RF and LO inputs
require only DC-blocking capacitors for interfacing.
Exposed Pad RF/Thermal Considerations
The exposed paddle (EP) of the MAX9986’s 20-pin thin
QFN-EP package provides a low thermal-resistance
path to the die. It is important that the PC board on
which the MAX9986 is mounted be designed to con-
duct heat from the EP. In addition, provide the EP with
a low-inductance path to electrical ground. The EP
MUST be soldered to a ground plane on the PC board,
either directly or through an array of plated via holes.
The IF output impedance is 200Ω (differential). For
evaluation, an external low-loss 4:1 (impedance ratio)
balun transforms this impedance down to a 50Ω single-
ended output (see the Typical Application Circuit).
Bias Resistors
Bias currents for the LO buffer and the IF amplifier are
optimized by fine tuning resistors R1 and R2. If
reduced current is required at the expense of perfor-
mance, contact the factory for details. If the 1% bias
resistor values are not readily available, substitute stan-
dard 5% values.
Chip Information
TRANSISTOR COUNT: 1017
PROCESS: SiGe BiCMOS
LEXT Inductor
LEXT serves to improve the LO-to-IF and RF-to-IF leak-
age. The inductance value can be adjusted by the user to
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