Table 1. component values – Rainbow Electronics MAX19998 User Manual
Page 26
SiGe, High-Linearity, 2300MHz to 4000MHz
Downconversion Mixer with LO Buffer
MAX19998
26 _____________________________________________________________________________________
Table 1. Component Values
LEXT Inductor
Short LEXT to ground using a 0I resistor. For applica-
tions requiring improved RF-to-IF and LO-to-IF isolation,
L3 can be changed to optimize performance (see the
Typical Operating Characteristics). 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 approximately 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 pos-
sible 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 per-
formance, 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 MAX19998 evaluation kit can be used
as a reference for board layout. Gerber files are available
upon request at
.
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 for component values.
*Use larger value inductors and a TC4-1W-7A 4:1 balun for IF frequencies below 200MHz.
DESIGNATION
QTY
DESCRIPTION
COMPONENT SUPPLIER
C1
1
8.2pF microwave capacitor (0402). Use for RF
frequencies ranging from 3000MHz to 4000MHz.
Murata Electronics North America, Inc.
3.3nH microwave inductor (0402). Use for RF
frequencies ranging from 2300MHz to 2900MHz.
Coilcraft, Inc.
C2, C6, C8, C11
4
0.01FF 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.
C16
1
Not installed for RF frequencies ranging from
3000MHz to 4000MHz
—
0.3pF microwave capacitor (0402). Use for RF
frequencies ranging from 2300MHz to 2900MHz.
Murata Electronics North America, Inc.
L1, L2
2
390nH wire-wound high-Q inductors* (0805)
Coilcraft, Inc.
L3
1
4.7nH wire-wound high-Q inductor (0603)
Coilcraft, Inc.
R1
1
698I Q1% resistor (0402). Use for V
CC
= 5.0V
applications.
Digi-Key Corp.
845I Q1% resistor (0402). Use for V
CC
= 3.3V
applications.
R2
1
604I Q1% resistor (0402). Use for V
CC
= 5.0V
applications.
Digi-Key Corp.
1.1kI Q1% resistor (0402). Use for V
CC
= 3.3V
applications.
R3
1
0I resistor (1206)
Digi-Key Corp.
T1
1
4:1 IF balun TC4-1W-17*
Mini-Circuits
U1
1
MAX19998 IC (20 Thin QFN-EP)
Maxim Integrated Products, Inc.