MAX2681(1998) Ver la hoja de datos (PDF) - Maxim Integrated
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MAX2681 Datasheet PDF : 12 Pages
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400MHz to 2.5GHz, Low-Noise,
SiGe Downconverter Mixers
Detailed Description
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.
Applications Information
Local-Oscillator (LO) Input
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).
RF Input
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
PART
MAX2680
MAX2681
MAX2682
400MHz
179-j356
209-j332
206-j306
FREQUENCY
900MHz 1950MHz 2450MHz
54-j179 32-j94
33-j73
75-j188 34-j108
33-j86
78-j182 34-j106
29-j86
IF Output
The IF output frequency range extends from 10MHz to
500MHz. IFOUT is a high-impedance, open-collector
output that requires an external inductor to VCC for
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.
Power-Supply and SHDN Bypassing
Proper attention to voltage supply bypassing is essen-
tial for high-frequency RF circuit stability. Bypass VCC
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.
Layout Issues
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 2. RF Input Impedance-Matching Component Values
MATCHING
COMPONENTS
Z1
Z2
Z3
400
MHz
86nH
270pF
Open
MAX2680
900 1950
MHz MHz
270pF 1.5pF
22nH 270pF
Open 1.8nH
2450
MHz
Short
270pF
1.8nH
400
MHz
68nH
270pF
0.5pF
FREQUENCY
MAX2681
900
MHz
1950
MHz
270pF 1.5pF
18nH 270pF
Open 1.8nH
2450
MHz
Short
270pF
2.2nH
400
MHz
68nH
270pF
0.5pF
MAX2682
900
MHz
1950
MHz
1.5pF Short
270pF 270pF
10nH 2.2nH
2450
MHz
Short
270pF
1.2nH
Note: Z1, Z2, and Z3 are found in the Typical Operating Circuit.
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