MAX2660/MAX2661/MAX2663/MAX2671/MAX2673
400MHz to 2.5GHz Upconverter Mixers
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_______________Detailed Description
The MAX2660/MAX2661/MAX2663/MAX2671/MAX2673
are 2.5GHz double-balanced upconverter mixers
designed to provide optimum linearity performance for
a specified supply current. These upconverter mixers
use single-ended RF, LO, and IF port connections,
except for the MAX2673, which uses a differential IF
port. An on-chip bias cell provides a low-power shut-
down feature. See the Selector Guide for device fea-
tures and comparison.
__________Applications Information
Local-Oscillator (LO) Input
The LO input is a single-ended broadband port with a
return loss of better than 8dB from 600MHz to 2.5GHz.
The LO signal is mixed with the input IF signal, and the
resulting upconverted output appears on the RFOUT
pin. AC-couple the LO pin with a capacitor having less
than 3Ω reactance at the LO frequency. The
MAX2671/MAX2673 include an internal LO buffer and
require an LO signal ranging from -10dBm to +5dBm,
while the MAX2660/MAX2661/MAX2663 require an LO
signal ranging from -5dBm to +2dBm.
IF Input
The MAX2660/MAX2661/MAX2663/MAX2671 have a
single-ended IF input port, while the MAX2673 has a
differential IF input port for high-performance interface-
to-differential IF filters. AC-couple the IF pin(s) with a
capacitor. The typical IF input frequency range is
40MHz to 500MHz. For further information, see the IF
Port Impedance vs. IF Frequency graph in the Typical
Operating Characteristics.
RF Output
The RF output frequency range extends from 400MHz
to 2.5GHz. RFOUT is a high-impedance, open-collector
output that requires an external inductor to V
CC
for
proper biasing. For optimum performance, implement
an impedance-matching network. The configuration
and values for the matching network depend on the fre-
quency, performance, and desired output impedance.
For assistance in choosing components for optimal per-
formance, see Table 1 as well as the RF Output
Impedance vs. RF Frequency graph in the Typical
Operating Characteristics.
Power Supply and
SSHHDDNN
Bypassing
Proper attention to supply bypassing is essential for a
high-frequency RF circuit. Bypass V
CC
with a 10µF
capacitor in parallel with an RF capacitor (Table 2). 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 connec-
tions.
Decouple SHDN with a 100pF 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 RFOUT
matching network.
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 V
CC
node. The V
CC
traces branch out from this central
node, each going to a separate V
CC
node in 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 each V
CC
pin. At high frequencies, any signal leaking out of one
supply pin sees a relatively high impedance (formed by
the V
CC
trace inductance) to the central V
CC
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 RFOUT matching network is very sensitive to lay-
out-related parasitics. To minimize parasitic induc-
tance, keep all traces short and place components as
close as possible to the chip. To minimize parasitic
capacitance, use cutouts in the ground plane (and any
other plane) below the matching network components.
