max2023etxt Maxim Integrated Products, Inc., max2023etxt Datasheet - Page 9

• Manufacturer Part Number: max2023etxt
• Description: Max2023 High-dynamic-range, Direct Up-/downconversion 1500mhz To 2300mhz Quadrature Mod/demod
• Manufacturer: Maxim Integrated Products, Inc.

The MAX2023 modulator is composed of a pair of
matched double-balanced passive mixers and a balun.
The I and Q differential baseband inputs accept signals
from DC to 450MHz with differential amplitudes up to
4V
MAX2023 as either a direct RF modulator or as an
image-reject mixer. The wide common-mode compli-
ance range allows for direct interface with the base-
band DACs. No active buffer circuitry is required
between the baseband DACs and the MAX2023 for
wideband applications.
The I and Q signals directly modulate the 0° and 90° LO
signals and are upconverted to the RF frequency. The out-
puts of the I and Q mixers are combined through a balun
to produce a singled-ended RF output.
The LO input of the MAX2023 is internally matched to
50Ω, and requires a single-ended drive at a 1500MHz
to 2300MHz frequency range. An integrated balun con-
verts the singled-ended input signal to a differential sig-
nal at the LO buffer differential input. An external
DC-blocking capacitor is the only external part required
at this interface. The LO input power should be within
the -3dBm to +3dBm range. An LO input power of
0dBm is recommended for best overall peformance.
Drive the MAX2023 I and Q baseband inputs differen-
tially for best performance. The baseband inputs have
a 50Ω differential input impedance. The optimum
source impedance for the I and Q inputs is 100Ω differ-
ential. This source impedance achieves the optimal sig-
nal transfer to the I and Q inputs, and the optimum
output RF impedance match. The MAX2023 can accept
input power levels of up to +20dBm on the I and Q
inputs. Operation with complex waveforms, such as
CDMA carriers or GSM signals, utilize input power lev-
els that are far lower. This lower power operation is
made necessary by the high peak-to-average ratios of
these complex waveforms. The peak signals must be
kept below the compression level of the MAX2023. The
input common-mode voltage should be confined to the
-3.5V to +3.5V DC range.
The MAX2023 is designed to interface directly with
Maxim high-speed DACs. This generates an ideal total
transmitter lineup, with minimal ancillary circuit elements
required for widespread applications. Such DACs
include the MAX5875 series of dual DACs, and the
High-Dynamic-Range, Direct Up-/Downconversion
P-P
. The wide input bandwidths allow operation of the
1500MHz to 2300MHz Quadrature Mod/Demod
WCDMA Transmitter Applications
Applications Information
_________________________________________________________________________________________________
Baseband I/Q Input Drive
LO Input Drive
I/Q Modulator
MAX5895 dual interpolating DAC. These DACs have
ground-referenced differential current outputs. Typical
termination of each DAC output into a 50Ω load resistor
to ground, and a 10mA nominal DC output current
results in a 0.5V common-mode DC level into the modu-
lator I/Q inputs. The nominal signal level provided by
the DACs will be in the -12dBm range for a single
CDMA or WCDMA carrier, reducing to -18dBm per
carrier for a four-carrier application.
The I/Q input bandwidth is greater than 450MHz at
-0.5dB response. The direct connection of the DAC to
the MAX2023 ensures the maximum signal fidelity, with
no performance-limiting baseband amplifiers required.
The DAC output can be passed through a lowpass filter
to remove the image frequencies from the DAC’s output
response. The MAX5895 dual interpolating DAC can be
operated at interpolation rates up to x8. This has the
benefit of moving the DAC image frequencies to a very
high, remote frequency, easing the design of the base-
band filters. The DAC’s output noise floor and interpola-
tion filter stopband attenuation are sufficiently good to
ensure that the 3GPP noise floor requirement is met for
large frequency offsets, 60MHz for example, with no fil-
tering required on the RF output of the modulator.
Figure 1 illustrates the ease and efficiency of interfacing
the MAX2023 with a Maxim DAC, in this case the
MAX5895 dual 16-bit interpolating-modulating DAC.
Figure 1. MAX5895 DAC Interfaced with MAX2023 for
cdma2000 and WCDMA Base Stations
BBQ
BBI
DUAL 16-BIT INTERP DAC
OFFSET ADJUST
I/Q GAIN AND
MAX5895
FREQ
FREQ
50Ω
50Ω
50Ω
50Ω
LO
0°
RF MODULATOR
MAX2023
90°
∑
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