AD9764 Analog Devices, AD9764 Datasheet - Page 13

• Manufacturer Part Number: AD9764
• Manufacturer: Analog Devices

Specifications of AD9764

• Resolution (bits): 14bit
• Dac Update Rate: 125MSPS
• Dac Settling Time: 35ns
• Max Pos Supply (v): +5.5V
• Single-supply: Yes
• Dac Type: Current Out
• Dac Input Format: Par

Since the AD9764 is capable of being updated up to 125 MSPS,
the quality of the clock and data input signals are important in
achieving the optimum performance. Operating the AD9764
with reduced logic swings and a corresponding digital supply
(DVDD) will result in the lowest data feedthrough and on-chip
digital noise. The drivers of the digital data interface circuitry
should be specified to meet the minimum setup and hold times
of the AD9764 as well as its required min/max input logic level
thresholds.
Digital signal paths should be kept short and run lengths
matched to avoid propagation delay mismatch. The insertion
of a low value resistor network (i.e., 20
the AD9764 digital inputs and driver outputs may be helpful in
reducing any overshooting and ringing at the digital inputs that
contribute to data feedthrough. For longer run lengths and high
data update rates, strip line techniques with proper termination
resistors should be considered to maintain “clean” digital inputs.
The external clock driver circuitry should provide the AD9764
with a low jitter clock input meeting the min/max logic levels
while providing fast edges. Fast clock edges will help minimize
any jitter that will manifest itself as phase noise on a recon-
structed waveform. Thus, the clock input should be driven by
the fastest logic family suitable for the application.
Note, that the clock input could also be driven via a sine wave,
which is centered around the digital threshold (i.e., DVDD/2)
and meets the min/max logic threshold. This will typically result
in a slight degradation in the phase noise, which becomes more
noticeable at higher sampling rates and output frequencies.
Also, at higher sampling rates, the 20% tolerance of the digital
logic threshold should be considered since it will affect the effec-
tive clock duty cycle and, subsequently, cut into the required
data setup and hold times.
SLEEP MODE OPERATION
The AD9764 has a power-down function that turns off the
output current and reduces the supply current to less than
8.5 mA over the specified supply range of 2.7 V to 5.5 V and
temperature range. This mode can be activated by applying a
logic level “1” to the SLEEP pin. This digital input also con-
tains an active pull-down circuit that ensures the AD9764 re-
mains enabled if this input is left disconnected. The SLEEP
input with active pull-down requires <40 A of drive current.
The power-up and power-down characteristics of the AD9764
are dependent upon the value of the compensation capacitor
connected to COMP1. With a nominal value of 0.1 F, the
AD9764 takes less than 5 s to power down and approximately
3.25 ms to power back up. Note, the SLEEP MODE should not
be used when the external control amplifier is used as shown in
Figure 27.
POWER DISSIPATION
The power dissipation, P
several factors, including: (1) AVDD and DVDD, the power
supply voltages; (2) I
f
waveform. The power dissipation is directly proportional to the
analog supply current, I
I
Figure 30, and is insensitive to f
REV. B
CLOCK
DVDD
. I
, the update rate; and (4) the reconstructed digital input
AVDD
is directly proportional to I
OUTFS
AVDD
D
, of the AD9764 is dependent on
, the full-scale current output; (3)
, and the digital supply current,
CLOCK
.
OUTFS,
to 100 ) between
as shown in
–13–
Conversely, I
form, f
show I
(f
DVDD = 3 V, respectively. Note, how I
than a factor of 2 when DVDD is reduced from 5 V to 3 V.
OUT
/f
DVDD
CLOCK
CLOCK
30
25
20
15
10
18
16
14
12
10
5
0
8
6
4
2
0
0.01
Figure 31. I
Figure 32. I
8
6
4
2
0
0.01
2
as a function of full-scale sine wave output ratios
) for various update rates with DVDD = 5 V and
, and digital supply DVDD. Figures 31 and 32
DVDD
4
Figure 30. I
is dependent on both the digital input wave-
6
DVDD
DVDD
8
RATIO – f
RATIO – f
vs. Ratio @ DVDD = 5 V
vs. Ratio @ DVDD = 3 V
I
OUTFS
10
AVDD
0.1
0.1
OUT
– mA
OUT
12
vs. I
/f
/f
CLK
DVDD
CLK
14
OUTFS
is reduced by more
16
125MSPS
100MSPS
50MSPS
25MSPS
5MSPS
AD9764
125MSPS
100MSPS
50MSPS
25MSPS
5MSPS
18
20
1
1