MAX2022
High-Dynamic-Range, Direct Up/
Downconversion 1500MHz to 3000MHz
Quadrature Modulator/Demodulator
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.
I
L = 11nH
C = 2.2pF
50?
50?
MAX2022
RF MODULATOR
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.
Q
L = 11nH
C = 2.2pF LO
50?
50?
C = 2.2pF
90°
RF
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.
www.maximintegrated.com
Figure 3. Diplexer Network Recommended for UMTS
Transmitter Applications
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 50? 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 25? (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.
Maxim Integrated │ 21
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相关代理商/技术参数
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MAX2022ETX-T 功能描述:调节器/解调器 1.5GHz-2.5GHz Quad Mod/Demod RoHS:否 制造商:Texas Instruments 封装 / 箱体:PVQFN-N24 封装:Reel
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