Rainbow Electronics MAX19996 - Manual (Page 17)

MAX19996
LEXT Inductor
Short LEXT to ground using a 0Ω resistor. For applica-
tions requiring improved RF-to-IF and LO-to-IF isolation,
a 4.7nH low-ESR inductor can be connected from LEXT
to GND. However, the load impedance presented to the
mixer must be such that any capacitances from IF- and
IF+ to ground do not exceed several picofarads to
ensure stable operating conditions. Since approximate-
ly 120mA flows through LEXT, it is important to use a
low-DCR wire-wound inductor.
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.
The load impedance presented to the mixer must be
such that any capacitance from both IF- and IF+ to
ground does not exceed several picofarads. 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/thermal-conduction path for the device. Solder
the exposed pad on the bottom of the device package to
the PCB. The MAX19996 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 with
the capacitors shown in the Typical Application Circuit
and see Table 1.
Exposed Pad RF/Thermal Considerations
The exposed pad (EP) of the MAX19996’s 20-pin thin
QFN package provides a low thermal-resistance path
to the die. It is important that the PCB on which the
MAX19996 is mounted be designed to conduct 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 PCB, either directly
or through an array of plated via holes.
DESIGNATION QTY DESCRIPTION COMPONENT SUPPLIER
C1 1 8.2pF microwave capacitor (0402) Murata Electronics North America, Inc.
C2, C6, C8, C11 4 0.01µF microwave capacitors (0402) Murata Electronics North America, Inc.
C3, C9 0 Not installed, capacitors —
C10 1 2pF microwave capacitor (0402) Murata Electronics North America, Inc.
C13, C14 2 1000pF microwave capacitors (0402) Murata Electronics North America, Inc.
C15 1 82pF microwave capacitor (0402) Murata Electronics North America, Inc.
L1, L2 2
120nH wire-wound high-Q inductors* (0805)
(see the Typical Operating Characteristics)
Coilcraft, Inc.
L3 1 4.7nH wire-wound high-Q inductor (0603) Coilcraft, Inc.
698 Ω ± 1% r esi stor ( 0402) . U se for V
C C
= +5 .0 V ap p l i cati ons.
R1 1
1.1k Ω ± 1% r esi stor ( 0402) . U se for V
C C = +3 .3 V ap p l i cati ons.
Digi-Key Corp.
604 Ω ± 1% r esi stor ( 0402) . U se for V
C C = +5 .0 V ap p l i cati ons.
R2 1
845 Ω ± 1% r esi stor ( 0402) . U se for V
C C = +3 .3 V ap p l i cati ons.
Digi-Key Corp.
R3 1 0 Ω resistor (1206) Digi-Key Corp.
T1 1 4:1 IF balun TC4-1W-17* Mini-Circuits
U1 1 MAX19996 IC (20 TQFN) Maxim Integrated Products, Inc.
Table 1. Component Values
* Use 470nH inductors and TC4-1W-7A 4:1 balun for IF frequencies below 200MHz.
SiGe High-Linearity, 2000MHz to 3000MHz
Downconversion Mixer with LO Buffer
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