MAX2682(1998) Ver la hoja de datos (PDF) - Maxim Integrated
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MAX2682 Datasheet PDF : 12 Pages
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400MHz to 2.5GHz, Low-Noise,
SiGe Downconverter Mixers
Table 3. IFOUT Port Impedance
PART
45MHz
FREQUENCY
70MHz
MAX2680
960-j372
803-j785
MAX2681
934-j373
746-j526
MAX2682
670-j216
578-j299
240MHz
186-j397
161-j375
175-j296
Table 4. IF Output Impedance-Matching
Components
MATCHING
COMPONENT
45MHz
FREQUENCY
70MHz
240MHz
L1
390nH
330nH
82nH
C2
39pF
15pF
3pF
R1
250Ω
Open
Open
Power-Supply Layout
To minimize coupling between different sections of the
IC, the ideal power-supply layout is a star configuration
with a large decoupling capacitor at a central VCC
node. The VCC traces branch out from this central
node, each going to a separate VCC node on the PC
board. At the end of each trace is a bypass capacitor
that has low ESR at the RF frequency of operation. This
arrangement provides local decoupling at the VCC pin.
At high frequencies, any signal leaking out of one sup-
ply pin sees a relatively high impedance (formed by the
VCC trace inductance) to the central VCC node, and an
even higher impedance to any other supply pin, as well
as a low impedance to ground through the bypass
capacitor.
Impedance-Matching Network Layout
The RFIN and IFOUT impedance-matching networks are
very sensitive to layout-related parasitics. To minimize
parasitic inductance, keep all traces short and place
components as close as possible to the chip. To mini-
mize parasitic capacitance, use cutouts in the ground
plane (and any other plane) below the matching network
components. However, avoid cutouts that are larger
than necessary since they act as aperture antennas.
Typical Operating Circuit
LO
INPUT
C1
1 LO
SHDN 6
2 GND
MAX2680
MAX2681
MAX2682
VCC 5
RF
Z1
INPUT
Z2
Z3
3 RFIN
4
IFOUT
SHUTDOWN
CONTROL
C3
L1
R1
C4
1000pF
VCC
+2.7V TO +5.5V
C5
10µF
IF
OUTPUT
C2
THE VALUES OF MATCHING COMPONENTS C2, L1, R1, Z1, Z2, AND Z3 DEPEND ON THE IF AND RF FREQUENCY AND DOWNCONVERTER. SEE TABLES 2 AND 4.
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