AD9760ARU Analog Devices Inc, AD9760ARU Datasheet - Page 18

• Manufacturer Part Number: AD9760ARU
• Description: IC DAC 10BIT 125MSPS 28-TSSOP
• Manufacturer: Analog Devices Inc
• Series: TxDAC®r

Specifications of AD9760ARU

• Settling Time: 35ns
• Rohs Status: RoHS non-compliant
• Number Of Bits: 10
• Number Of Converters: 1
• Voltage Supply Source: Analog and Digital
• Power Dissipation (max): 175mW
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-TSSOP
• Number Of Channels: 1
• Resolution: 10b
• Interface Type: Parallel
• Single Supply Voltage (typ): 5V
• Dual Supply Voltage (typ): Not RequiredV
• Power Supply Requirement: Analog and Digital
• Output Type: Current
• Single Supply Voltage (min): 2.7V
• Single Supply Voltage (max): 5.5V
• Dual Supply Voltage (min): Not RequiredV
• Dual Supply Voltage (max): Not RequiredV
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 28
• For Use With: AD9760-EBZ - BOARD EVAL FOR AD9760
• Data Interface: -
• Lead Free Status / RoHS Status: Not Compliant

AD9760
APPLICATIONS
Using the AD9760 for QAM Modulation
QAM is one of the most widely used digital modulation schemes
in digital communication systems. This modulation technique
can be found in both FDM spreadspectrum (i.e., CDMA) based
systems. A QAM signal is a carrier frequency that is both
modulated in amplitude (i.e., AM modulation) and in phase
(i.e., PM modulation). It can be generated by independently
modulating two carriers of identical frequency but with a 90°
phase difference. This results in an in-phase (I) carrier compo-
nent and a quadrature (Q) carrier component at a 90° phase
shift with respect to the I component. The I and Q components
are then summed to provide a QAM signal at the specified car-
rier frequency.
A common and traditional implementation of a QAM modu-
lator is shown in Figure 56. The modulation is performed in the
analog domain in which two DACs are used to generate the
baseband I and Q components, respectively. Each component is
then typically applied to a Nyquist filter before being applied to
a quadrature mixer. The matching Nyquist filters shape and
limit each component’s spectral envelope while minimizing
intersymbol interference. The DAC is typically updated at the
QAM symbol rate or possibly a multiple of it if an interpolating
filter precedes the DAC. The use of an interpolating filter typi-
cally eases the implementation and complexity of the analog
filter, which can be a significant contributor to mismatches in
gain and phase between the two baseband channels. A quadra-
ture mixer modulates the I and Q components with in-phase
and quadrature phase carrier frequency and sums the two out-
puts to provide the QAM signal.
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 57 helps improve
on the matching and temperature stability characteristics be-
tween the I and Q channels. 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 stability. Further enhance-
ments in gain matching and stability are achieved by using sepa-
rate matching resistor networks for both R
Additional trim capability via R
compensate for any initial mismatch in gain between the two
channels. This may be attributed to any mismatch between U1
and U2’s gain setting resistor (R
(R
The differential voltage outputs of U1 and U2 are fed into their
respective differential inputs of a quadrature mixer via matching
50 Ω filter networks.
It is also possible to generate a QAM signal completely in the
digital domain via a DSP or ASIC, in which case only a single
DAC of sufficient resolution and performance is required to
reconstruct the QAM signal. Also available from several vendors
LOAD
ASIC
DSP
OR
), and/or voltage offset of each DAC’s control amplifier.
Figure 56. Typical Analog QAM Architecture
10
10
AD9760
AD9760
FREQUENCY
CARRIER
NYQUIST
FILTERS
CAL1
SET
), effective load resistance,
and R
QUADRATURE
MODULATOR
CAL2
0
SET
90
can be added to
and R
Σ
LOAD
TO
MIXER
.
–18–
are Digital ASICs which implement other digital modulation
schemes such as PSK and FSK. This digital implementation has
the benefit of generating perfectly matched I and Q components
in terms of gain and phase, which is essential in maintaining
optimum performance in a communication system. In this
implementation, the reconstruction DAC must be operating at a
sufficiently high clock rate to accommodate the highest specified
QAM carrier frequency. Figure 58 shows a block diagram of
such an implementation using the AD9760.
AD9760 EVALUATION BOARD
General Description
The AD9760-EB is an evaluation board for the AD9760 10-bit
D/A converter. Careful attention to layout and circuit design,
combined with a prototyping area, allow the user to easily and
effectively evaluate the AD9760 in any application where high
resolution, high speed conversion is required.
This board allows the user the flexibility to operate the AD9760
in various configurations. Possible output configurations include
transformer coupled, resistor terminated, inverting/noninverting
and differential amplifier outputs. The digital inputs are designed
to be driven directly from various word generators with the on-
board option to add a resistor network for proper load termina-
tion. Provisions are also made to operate the AD9760 with
either the internal or external reference or to exercise the power-
down feature.
Refer to the application note AN-420, “Using the AD9760/
AD9760/AD9764-EB Evaluation Board,” for a thorough
description and operating instructions for the AD9760 evalua-
tion board.
FREQUENCY
Figure 57. Baseband QAM Implementation Using Two
AD9760s
R
CARRIER
0.1 F
R
100
2k *
CAL2
R
2k *
R
CAL1
50
Q DATA
SET
I DATA
SET
12
12
12
Figure 58. Digital QAM Architecture
SIN
CLOCK
REFIO
12
STEL-1177
FS ADJ
REFIO
STEL-1130
FS ADJ
** OHMTEK TOMC1603-50F
QAM
NCO
* OHMTEK ORNA1001F
12
REFLO
COS
AVDD
REFLO
Q-CHANNEL
I-CHANNEL
CLOCK
10
U1
U2
CLOCK
CLOCK
AD9760
I
I
I
I
OUTA
OUTB
OUTA
OUTB
50 **
R
50 **
R
LOAD
50
LOAD
50 **
R
50 **
R
LOAD
LOAD
LPF
TO
NYQUIST
FILTER
AND MIXER
TO
NYQUIST
FILTER
AND MIXER
REV. B
50
TO
MIXER