AD9712BAN Analog Devices, AD9712BAN Datasheet - Page 7

• Manufacturer Part Number: AD9712BAN
• Description: 12-Bit/ 100 MSPS D/A Converters
• Manufacturer: Analog Devices

REV. B
An operational amplifier can also be used to perform the I to V
conversion of the DAC output. Figure 5 shows an example of a
circuit which uses the AD9617, a high speed, current feedback
amplifier.
GROUND
SYSTEM
–5.2V
+
1/2 AD708
–
Figure 5. I/VConversion Using Current Feedback
LOGIC
Figure 4. Typical Resistive Load Connection
DRIVE
ECL
0.1µF
REF
OUT
20
AD9712B
AD9713B
CONTROL
AMP IN
10k
28
10
11
26
1
2
5
6
3
4
7
8
9
ANALOG
19
RETURN
I
I
OUT
OUT
0.1µF
LATCH ENABLE
D
D
D
D
D
D
D
D
D
D
13
D
0.01µF
DIGITAL –V
11
12
10
2
6
7
9
4
5
8
1
1/2 AD708
14
16
(MSB)
(LSB)
–
+
12,21
I
FS
REFERENCE
10k
0.01µF
GROUND
12.5
S
22
25
R
REFERENCE
REFERENCE
ANALOG –V
AD9712B
AD9713B
L
CONTROL
CONTROL
AMP OUT
R
25
15,25
FF
AMP IN
GROUND
DIGITAL
R
R
I
I
OUT
100
OUT
OUT
1
R
SET
27
200
IN
2
S
17
24
16
14
18
19
20
I
+
–
AD9617
OS
R
400
FB
R
R
20
0.1µF
L
L
I
V
FS
V
±2.048V
OUT
OUT
x R
=
L
–7–
DAC current across feedback resistor R
AD9617 output swing. A current divider formed by R
limits the current used in the I-to-V conversion, and provides an
output voltage swing within the specifications of the AD9617.
Current through R
AD9617. Adjusting the value of R
current. This offset current is based on the reference of the
AD9712B/AD9713B, to avoid coupling noise into the output
signal.
The resistor values in Figure 5 provide a 4.096 V swing, cen-
tered at ground, at the output of the AD9617 amplifier.
Power and Grounding
Maintaining low noise on power supplies and ground is critical
for obtaining optimum results with the AD9712B or AD9713B.
DACs are most often used in circuits which are predominantly
digital. To preserve 12-bit performance, especially at conversion
speeds up to 100 MSPS, special precautions are necessary for
power supplies and grounding.
Ideally, the DAC should have a separate analog ground plane.
All ground pins of the DAC, as well as reference and analog
output components, should be tied directly to this analog
ground plane. The DAC’s ground plane should be connected to
the system ground plane at a single point.
Ferrite beads such as the Stackpole 57-1392 or Amidon
FB-43B-101, along with high frequency, low-inductance decou-
pling capacitors, should be used for the supply connections to
isolate digital switching currents from the DAC supply pins.
Separate isolation networks for the digital and analog supply
connections will further reduce supply noise coupling to the
output.
Molded socket assemblies should be avoided even when
prototyping circuits with the AD9712B or AD9713B. When
the DAC cannot be directly soldered into the board, individual
pin sockets such as AMP #6-330808-0 (knock-out end), or
#60330808-3 (open end) should be used. These have much
less effect on inter-lead capacitance than do molded assemblies.
DDS Applications
Numerically controlled oscillators (NCOs) are digital devices
which generate samples of a sine wave. When the NCO is com-
bined with a high performance D/A converter (DAC), the com-
bination system is referred to as a Direct Digital Synthesizer
(DDS).
The digital samples generated by the NCO are reconstructed by
the DAC and the resulting sine wave is usable in any system
which requires a stable, spectrally pure, frequency-agile refer-
ence. The DAC is often the limiting factor in DDS applications,
since it is the only analog function in the circuit. The AD9712B/
AD9713B D/A converters offer the highest level of performance
available for DDS applications.
DC linearity errors of a DAC are the dominant effect in low-
frequency applications and can affect both noise and harmonic
content in the output waveform. Differential Nonlinearity
(DNL) errors determine the quantization error between adja-
cent codes, while Integral Nonlinearity (INL) is a measure of
how closely the overall transfer function of the DAC compares
with an ideal device. Together, these errors establish the limits
of phase and amplitude accuracy in the output waveform.
2
provides dc offset at the output of the
AD9712B/AD9713B
1
adjusts the value of offset
FB
determines the
L
and R
FF