Rainbow Electronics MAX19999 - Manual (Page 16)

MAX19999
Dual, SiGe High-Linearity, 3000MHz to
4000MHz Downconversion Mixer with LO Buffer
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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 is typically +24dBm, 74dBc, and
10.5dB, respectively, for low-side LO injection architec-
tures covering the 3000MHz to 4000MHz RF band.
Differential IF Output Amplifier
The MAX19999 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 compo-
nents, and PCB to provide an optimized IF match at the
frequency of interest. Note that differential IF outputs
are ideal for providing enhanced 2RF-2LO 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, the IF return loss is typically 18dB.
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 3000MHz to 4000MHz. RF and LO inputs
require only DC-blocking capacitors for interfacing.
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 MAX19999 has two pins (LO_ADJ,
IF_SET) that allow external resistors to set the internal
bias currents. Nominal values for these resistors are
given in Table 1. Larger valued resistors can be used to
reduce power dissipation at the expense of some per-
formance loss. If ±1% resistors are not readily avail-
able, ±5% resistors can be substituted.
Significant reductions in power consumption can also
be realized by operating the mixer with an optional sup-
ply 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 trade-offs.
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 MAX19999 evaluation kit can be used as a refer-
ence 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 with
the capacitors shown in the Typical Application Circuit .
Exposed Pad RF/Thermal Considerations
The exposed pad (EP) of the MAX19999’s 36-pin thin
QFN-EP package provides a low thermal-resistance
path to the die. It is important that the PCB on which the
MAX19999 is mounted be designed to conduct heat
from the exposed pad. In addition, provide the exposed
pad with a low-inductance path to electrical ground.
The exposed pad MUST be soldered to a ground plane
on the PCB, either directly or through an array of plated
via holes.