Datasheet

Maxim Integrated │ 19
MAX2022 High-Dynamic-Range, Direct Up/
Downconversion 1500MHz to 3000MHz
Quadrature Modulator/Demodulator
www.maximintegrated.com
Modulator Baseband I/Q Input Drive
The MAX2022 I and Q baseband inputs should be driven
differentially for best performance. The baseband inputs
have a 50Ω differential input impedance. The optimum
sourceimpedancefortheIandQinputsis100Ωdifferen-
tial. This source impedance will achieve the optimal signal
transfer to the I and Q inputs, and the optimum output RF
impedance match. The MAX2022 can accept input power
levels of up to +12dBm on the I and Q inputs. Operation
with complex waveforms, such as CDMA or WCDMA
carriers, utilize input power levels 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 MAX2022. The input common-mode voltage should
be confined to the -2V to +1.5V DC range.
The MAX2022 is designed to interface directly with Maxim
high-speed DACs. This generates an ideal total transmit-
ter lineup, with minimal ancillary circuit elements. Such
DACs include the MAX5875 series of dual DACs, and
the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 modulator 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 50MHz at -0.1dB
response. The direct connection of the DAC to the
MAX2022 insures 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 ben-
efit of moving the DAC image frequencies to a very high,
remote frequency, easing the design of the baseband
filters. The DAC’s output noise floor and interpolation
filter stopband attenuation are sufficiently good to insure
that the 3GPP noise floor requirement is met for large
frequency offsets, 60MHz for example, with no filtering
required on the RF output of the modulator.
Figure 1 illustrates the ease and efficiency of interfac-
ing the MAX2022 with a Maxim DAC, in this case the
MAX5895dual16-bitinterpolating-modulatingDAC.
The MAX5895 DAC has programmable gain and dif-
ferential offset controls built in. These can be used to
optimize the LO leakage and sideband suppression of the
MAX2022 quadrature modulator.
Figure 1. MAX5895 DAC Interfaced with MAX2022
MAX5895
DUAL 16-BIT INTERP DAC
MAX2022
RF MODULATOR
I/Q GAIN AND
OFFSET ADJUST
BBI
LO
BBQ
FREQ
50Ω
50Ω
50Ω
FREQ
50Ω
50Ω
RF
50Ω
0°
90°
∑