AD9752ARURL7 Analog Devices Inc, AD9752ARURL7 Datasheet - Page 17

• Manufacturer Part Number: AD9752ARURL7
• Description: IC DAC 12BIT 125MSPS 28-TSSOP
• Manufacturer: Analog Devices Inc
• Series: TxDAC®r

Specifications of AD9752ARURL7

• Rohs Status: RoHS non-compliant
• Settling Time: 35ns
• Number Of Bits: 12
• Data Interface: Parallel
• Number Of Converters: 1
• Voltage Supply Source: Analog and Digital
• Power Dissipation (max): 220mW
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-TSSOP

In this implementation, it is much more difficult to maintain
proper gain and phase matching between the I and Q channels.
The circuit implementation shown in Figure 37 helps improve
upon the matching and temperature stability characteristics
between the I and Q channels, as well as showing a path for up-
conversion using the AD8346 quadrature modulator. Using a
single voltage reference derived from U1 to set the gain for both
the I and Q channels will improve the gain matching and stabil-
ity. R
between the two channels. This mismatch may be attributed to
the mismatch between R
of each channel, and/or the voltage offset of the control ampli-
fier in each DAC. The differential voltage outputs of U1 and U2
are fed into the respective differential inputs of the AD8346 via
matching networks.
Using the same matching techniques described above, Figure 38
shows an example of the AD9752 used in a W-CDMA transmit-
ter application using the AD6122 CDMA 3 V transmitter IF
REV. 0
ASIC
DSP
OR
CAL
Figure 36. Typical Analog QAM Architecture
can be used to compensate for any mismatch in gain
12
12
AD9752
AD9752
Q DATA
R
2k
I DATA
INPUT
INPUT
FSADJ
SET1
REFIO
SET1
CLK
FREQUENCY
0.1 F
CARRIER
and R
NYQUIST
FILTERS
REFIO
Figure 37. Baseband QAM Implementation Using Two AD9752s
REFLO
(“Q DAC”)
(“I DAC”)
AD9752
LATCHES
AD9752
LATCHES
SET2
R
1.9k
SET2
, effective load resistance
FSADJ
DVDD
AVDD
QUADRATURE
MODULATOR
0
ACOM
R
220
90
CAL
DAC
DAC
U1
U2
REFLO
SLEEP
AVDD
QOUTA
QOUTB
IOUTB
IOUTA
DCOM
AVDD
TO
MIXER
100W
100
100
100
C
NOTE: 500
100
FILTER
500
–17–
500
C
500
FILTER
RESISTOR NETWORK - TOMC1603-100D
500
500
subsystem. The AD6122 has functions, such as external gain
control and low distortion characteristics, needed for the supe-
rior Adjacent Channel Power (ACP) requirements of W-CDMA.
CDMA
Carrier Division Multiple Access, or CDMA, is an air transmit/
receive scheme where the signal in the transmit path is modu-
lated with a pseudorandom digital code (sometimes referred to
as the spreading code). The effect of this is to spread the trans-
mitted signal across a wide spectrum. Similar to a DMT wave-
form, a CDMA waveform containing multiple subscribers can
be characterized as having a high peak to average ratio (i.e.,
crest factor), thus demanding highly linear components in the
transmit signal path. The bandwidth of the spectrum is defined
by the CDMA standard being used, and in operation is imple-
mented by using a spreading code with particular characteristics.
Distortion in the transmit path can lead to power being trans-
mitted out of the defined band. The ratio of power transmitted
in-band to out-of-band is often referred to as Adjacent Channel
Power (ACP). This is a regulatory issue due to the possibility of
interference with other signals being transmitted by air. Regula-
tory bodies define a spectral mask outside of the transmit band,
and the ACP must fall under this mask. If distortion in the
transmit path cause the ACP to be above the spectral mask,
then filtering, or different component selection is needed to
meet the mask requirements.
500
500mV p-p WITH
+5V
RESISTOR NETWORK - OHMTEK ORN5000D
500
V
634
CM
=1.2V
500
0.1 F
BBIP
BBIN
BBQP
BBQN
VPBF
1.82V
SPLITTER
PHASE
AD8346
+
LOIP
LOIN
VOUT
AD9752