4 0 0 MHz t o 2 .5 GHz, Lo w -No is e ,
S iGe Do w n c o n ve rt e r Mix e rs
01/MAX682
IF Ou t p u t
De t a ile d De s c rip t io n
The IF output frequency range extends from 10MHz to
500MHz. IFOUT is a high-impedance, open-collector
The MAX2680/MAX2681/MAX2682 a re 400MHz to
2.5GHz, silicon-germanium, double-balanced down-
converter mixers. They are designed to provide opti-
mum line a rity p e rforma nc e for a s p e c ifie d s up p ly
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.
output that requires an external inductor to V
for
CC
proper biasing. For optimum performance, the IF port
requires an impedance-matching network. The configu-
ration and values for the matching network is depen-
d e nt up on the fre q ue nc y a nd d e s ire d outp ut
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.
Ap p lic a t io n s In fo rm a t io n
SHDN
P o w e r-S u p p ly a n d
Proper attention to voltage supply bypassing is essen-
tial for high-frequency RF circuit stability. Bypass V
Byp a s s in g
Lo c a l-Os c illa t o r (LO) In p u t
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
p ort with a s ig na l ra ng ing from -10d Bm to 0 (50Ω
source).
CC
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.
RF In p u t
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.
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.
La yo u t Is s u e s
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.
Table 1. RFIN Port Impedance
FREQUENCY
PART
400MHz
179-j356
209-j332
206-j306
900MHz
54-j179
75-j188
78-j182
1950MHz
2450MHz
33-j73
MAX2680
MAX2681
MAX2682
32-j94
34-j108
34-j106
33-j86
29-j86
Table 2. RF Input Impedance-Matching Component Values
FREQUENCY
MAX2680
MAX2681
MAX2682
MATCHING
COMPONENTS
400
MHz
900
MHz
1950
MHz
2450
MHz
400
MHz
900
1950
MHz
2450
MHz
400
MHz
900
1950
MHz
2450
MHz
MHz
270pF
18nH
Open
MHz
1.5pF
270pF
10nH
Z1
Z2
Z3
86nH
270pF
Open
270pF 1.5pF
Short
68nH
1.5pF
Short
68nH
Short
Short
22nH
Open
270pF 270pF 270pF
1.8nH 1.8nH 0.5pF
270pF 270pF 270pF
1.8nH 2.2nH 0.5pF
270pF 270pF
2.2nH 1.2nH
Note: Z1, Z2, and Z3 are found in the Typical Operating Circuit.
_______________________________________________________________________________________
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