AD9772A Analog Devices, AD9772A Datasheet - Page 18

• Manufacturer Part Number: AD9772A
• Manufacturer: Analog Devices

Specifications of AD9772A

• Resolution (bits): 14bit
• Dac Update Rate: 160MSPS
• Dac Settling Time: 11ns
• Max Pos Supply (v): +3.6V
• Single-supply: Yes
• Dac Type: Current Out
• Dac Input Format: Par

AD9772A
In many band-limited applications, the images from the
reconstruction process must be suppressed by an analog filter
following the DAC. The complexity of this analog filter is typically
determined by the proximity of the desired fundamental to the
first image and the required amount of image suppression.
Adding to the complexity of this analog filter is the requirement
of compensating for the sin(x)/x response of the DAC.
Referring to Figure 27, the new first image associated with the
higher data rate of the DAC after interpolation is pushed out
further relative to the input signal, because it now occurs at 2×
f
lower DAC data rate before interpolation is suppressed by the
digital filter. As a result, the transition band for the analog
reconstruction filter is increased, thus reducing the complexity
of the analog filter. Furthermore, the value of the sin(x)/x roll-
off divided by the original input data pass band (that is, dc to
f
As previously mentioned, the 2× interpolation filter can be
converted into a high-pass response, thus suppressing the fun-
damental while passing the original first image occurring at
f
DATA
DATA
DATA
/2) is significantly reduced.
− f
− f
FUNDAMENTAL
FUNDAMENTAL
. The old first image associated with the
. Figure 28 shows the time and frequency
FREQUENCY
FREQUENCY
f
f
DOMAIN
DOMAIN
FUNDAMENTAL
DOMAIN
DOMAIN
FUNDAMENTAL
Figure 28. Time and Frequency Domain Example of High-Pass 2× Digital Interpolation Filter
Figure 27. Time and Frequency Domain Example of Low-Pass 2× Digital Interpolation Filter
TIME
TIME
1/
1/
INPUT DATA
f
INPUT DATA
f
DATA
DATA
LATCH
LATCH
f
f
DATA
DATA
FIRST IMAGE
f
f
DATA
DATA
FIRST IMAGE
2 ×
2 ×
f
f
DATA
DATA
f
SUPPRESSED
f
FUNDAMENTAL
FUNDAMENTAL
Rev. C | Page 18 of 40
SUPPRESSED
FIRST IMAGE
LOWER IMAGE
2× INTERPOLATION
2× INTERPOLATION
UPPER AND
RESPONSE
f
DIGITAL
f
FILTER
DATA
2 ×
DATA
2 ×
FILTER
FILTER
1/ 2 ×
2×
1/2 ×
2×
f
f
representation for a high-pass response of a discrete time sine
wave. This action can also be modeled as a half-wave digital
mixing process in which the impulse response of the low-pass
filter is digitally mixed with a square wave having a frequency of
exactly f
value of 0 (see Table 5), this process simplifies into inverting the
center coefficient of the low-pass filter (that is, inverting H(18)).
Note that this also corresponds to inverting the peak of the
impulse response shown in Figure 4. The resulting high-pass
frequency response becomes the frequency inverted mirror
image of the low-pass filter response shown in Figure 5.
Note that the new first image occurs at f
reduced transition region of 2 × f
selection, thus mandating that the f
sufficiently high for practical filtering purposes in direct IF
applications. In addition, the lower sideband images occurring
at f
f
sideband images occurring at f
(that is, N × f
DATA
DATA
FUNDAMENTAL
f
f
DATA
DATA
DATA
FIRST IMAGE
2 ×
2 ×
RESPONSE
DIGITAL
FILTER
f
NEW
f
DATA
− f
DATA
DATA
FUNDAMENTAL
) experience a frequency inversion while the upper
/2. Because the even coefficients have an integer
DATA
+ f
FUNDAMENTAL
f
DAC SIN(x)/x
f
DATA
RESPONSE
DAC SIN(x)/x
and its multiples (that is, N × f
DATA
RESPONSE
DAC
DAC
2 ×
2 ×
DATA
f
f
DATA
DATA
) do not.
FUNDAMENTAL
+ f
FUNDAMENTAL
FUNDAMENTAL
DATA
+ f
exists for image
and its multiples
be placed
FUNDAMENTAL
DATA
−
. A