switched in. LO switching time is typically less than
50ns, which is more than adequate for virtually all GSM
applications. If frequency hopping is not employed, set
the switch to either of the LO inputs. The switch is con-
trolled by a digital input (LOSEL): logic-high selects
LO2, logic-low selects LO1. To avoid damage to the
part, voltage must be applied to V
CC
before digital logic
is applied to LOSEL. LO1 and LO2 inputs are internally
matched to 50Ω, requiring only a 22pF DC-
blocking capacitor.
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.
High-Linearity Mixer
The core of the MAX9996 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 26.5dBm, 72dBc, and 9.7dB,
respectively.
Differential IF Output Amplifier
The MAX9996 mixer has a 40MHz to 350MHz IF fre-
quency range. The differential, open-collector IF output
ports require external pullup inductors to V
CC
. Note that
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. After the balun, the IF return loss is bet-
ter than 15dB.
Applications Information
Input and Output Matching
The RF and LO inputs are internally matched to 50Ω.
No matching components are required. Return loss at
the RF port is typically 15dB over the entire input range
(1700MHz to 2200MHz) and return loss at the LO ports
is typically better than 16dB (1900MHz to 2400MHz).
RF and LO inputs require only DC-blocking capacitors
for interfacing.
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.
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
optimize the performance for a particular frequency
band. Since approximately 100mA 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 MAX9996 Evaluation Kit can be used as a
reference for board layout. Gerber files are available
upon request at www.maxim-ic.com.
Power-Supply Bypassing
Proper voltage-supply bypassing is essential for high-
frequency circuit stability. Bypass each V
CC
pin and
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.
MAX9996
SiGe High-Linearity, 1700MHz to 2200MHz
Downconversion Mixer with LO Buffer/Switch
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