Datasheet

Maxim Integrated │ 21
MAX2022 High-Dynamic-Range, Direct Up/
Downconversion 1500MHz to 3000MHz
Quadrature Modulator/Demodulator
www.maximintegrated.com
The DAC outputs must be filtered by baseband filters to
remove the image frequency signal components. The
baseband signals for four-carrier operation cover DC
to 10MHz. The image frequency appears at 481MHz to
491MHz. This very large frequency spread allows the
use of very low-complexity lowpass filters, with excellent
in-band gain and phase performance. The low DAC noise
floor allows for the use of a very wideband filter, since
thefilterisnotnecessarytomeetthe3GPPnoisefloor
specification.
The MAX2022 quadrature modulator then upconverts the
baseband signals to the RF output frequency. The output
power of the MAX2022 will be approximately -28dBm
percarrier.Thenoisefloorwillbelessthan-169dBm/Hz,
with an ACLR typically greater than 65dBc. This perfor-
mancemeetsthe 3GPPspecification requirements with
substantial margins. The noise floor performance will be
maintained for large offset frequencies, eliminating the
need for subsequent RF filtering in the transmitter lineup.
The RF output from the MAX2022 is then amplified by
a combination of a low-noise amplifier followed by a
MAX2057 RF-VGA. This VGA can be used for lineup
compensation for gain variance of transmitter and power
amplifier elements. No significant degradation of the
signal or noise levels will be incurred by this additional
amplification.TheMAX2057willdeliveranoutputpower
of -6dBm per carrier, 0dBm total at an ACLR of 65dB and
noise floor of -142dBc/Hz.
External Diplexer
LO leakage at the RF port can be nulled to a level less
than -80dBm by introducing DC offsets at the I and Q
ports. However, this null at the RF port can be compro-
mised by an improperly terminated I/Q interface. Care
must be taken to match the I/Q ports to the external
circuitry. Without matching, the LO’s second-order term
(2f
LO
) it may reflect back into the modulator’s I/Q ports
where it can remix with the internal LO signal to produce
additional LO leakage at the RF output. This reflection
effectively counteracts against the LO nulling. In addi-
tion, the LO signal reflected at the I/Q IF port produces
a residual DC term that can disturb the nulling condition.
As demonstrated in Figure 3, providing an RC termination
on each of the I+, I-, Q+, Q- ports reduces the amount of
LO leakage present at the RF port under varying tempera-
ture, LO frequency, and baseband termination conditions.
See the Typical Operating Characteristics for details. Note
thattheresistorvalueischosentobe50Ωwithacorner
frequency1/(2�RC)selectedtoadequatelyfilterthef
LO
and 2f
LO
leakage, yet not affecting the flatness of the
baseband response at the highest baseband frequency.
The common-mode f
LO
and 2f
LO
signals at I+/I- and
Q+/Q- effectively see the RC networks and thus become
terminatedin25Ω(R/2).TheRCnetworkprovidesapath
for absorbing the 2f
LO
and f
LO
leakage, while the induc-
tor provides high impedance at f
LO
and 2f
LO
to help the
diplexing process.
Figure 3. Diplexer Network Recommended for UMTS
Transmitter Applications
MAX2022
RF MODULATOR
LO
RF
50Ω
50Ω
L = 11nH
C = 2.2pF
∑
L = 11nH
I
Q
50Ω
50Ω
C = 2.2pF
C = 2.2pF
0°
90°