MAX2681 MAXIM [Maxim Integrated Products], MAX2681 Datasheet - Page 9

• Manufacturer Part Number: MAX2681
• Description: 400MHz to 2.5GHz, Low-Noise, SiGe Downconverter Mixers
• Manufacturer: MAXIM [Maxim Integrated Products]

The MAX2680/MAX2681/MAX2682 are 400MHz to
2.5GHz, silicon-germanium, double-balanced down-
converter mixers. They are designed to provide opti-
mum linearity performance for a specified supply
current. They consist of a double-balanced Gilbert-cell
mixer with single-ended RF, LO, and IF port connec-
tions. An on-chip bias cell provides a low-power shut-
down feature. Consult the Selector Guide for device
features and comparison.
The LO input is a single-ended broadband port with a
typical input VSWR of better than 2.0:1 from 400MHz to
2.5GHz. The LO signal is mixed with the RF input sig-
nal, and the resulting downconverted output appears at
IFOUT. AC-couple LO with a capacitor. Drive the LO
port with a signal ranging from -10dBm to 0 (50Ω
source).
The RF input frequency range is 400MHz to 2.5GHz.
The RF input requires an impedance-matching network
as well as a DC-blocking capacitor that can be part of
the matching network. Consult Tables 1 and 2, as well
as the RF Port Impedance vs. RF Frequency graph in
the Typical Operating Characteristics for information on
matching.
Table 1. RFIN Port Impedance
Table 2. RF Input Impedance-Matching Component Values
Note: Z1, Z2, and Z3 are found in the Typical Operating Circuit.
MAX2680
MAX2681
MAX2682
COMPONENTS
PART
MATCHING
Z1
Z2
Z3
179-j356
209-j332
206-j306
400MHz
Applications Information
_______________________________________________________________________________________
270pF
Open
86nH
MHz
400
Local-Oscillator (LO) Input
Detailed Description
900MHz
54-j179
75-j188
78-j182
270pF
Open
22nH
FREQUENCY
MHz
900
MAX2680
1950MHz
270pF
1.8nH
1.5pF
34-j108
34-j106
1950
MHz
32-j94
400MHz to 2.5GHz, Low-Noise,
270pF
1.8nH
Short
2450
MHz
RF Input
2450MHz
33-j73
33-j86
29-j86
SiGe Downconverter Mixers
270pF
0.5pF
68nH
MHz
400
270pF
Open
18nH
MHz
900
The IF output frequency range extends from 10MHz to
500MHz. IFOUT is a high-impedance, open-collector
output that requires an external inductor to V
proper biasing. For optimum performance, the IF port
requires an impedance-matching network. The configu-
ration and values for the matching network is depen-
dent upon the frequency and desired output
impedance. For assistance in choosing components for
optimal performance, refer to Tables 3 and 4 as well as
the IF Port Impedance vs. IF Frequency graph in the
Typical Operating Characteristics.
Proper attention to voltage supply bypassing is essen-
tial for high-frequency RF circuit stability. Bypass V
with a 10µF capacitor in parallel with a 1000pF capaci-
tor. Use separate vias to the ground plane for each of
the bypass capacitors and minimize trace length to
reduce inductance. Use separate vias to the ground
plane for each ground pin. Use low-inductance ground
connections.
Decouple SHDN with a 1000pF capacitor to ground to
minimize noise on the internal bias cell. Use a series
resistor (typically 100Ω) to reduce coupling of high-fre-
quency signals into the SHDN pin.
A well designed PC board is an essential part of an RF
circuit. For best performance, pay attention to power-
supply issues as well as to the layout of the RFIN and
IFOUT impedance-matching network.
FREQUENCY
MAX2681
270pF
1.5pF
1.8nH
1950
MHz
Power-Supply and
270pF
2.2nH
Short
2450
MHz
270pF
0.5pF
68nH
MHz
400
270pF
1.5pF
Layout Issues
10nH
MHz
900
S S H H D D N N Bypassing
MAX2682
270pF
2.2nH
Short
1950
MHz
IF Output
CC
270pF
1.2nH
2450
Short
MHz
for
CC
9