AD9243AS View Datasheet(PDF) - Analog Devices
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Description
Manufacturer
AD9243AS Datasheet PDF : 24 Pages
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AD9243
APPLICATIONS
DIRECT IF DOWN CONVERSION USING THE AD9243
As previously noted, the AD9243’s performance in the differen-
tial mode of operation extends well beyond its baseband region
and into several Nyquist zone regions. Hence, the AD9243 may
be well suited as a mix down converter in both narrow and
wideband applications. Various IF frequencies exist over the
frequency range in which the AD9243 maintains excellent dy-
namic performance (e.g., refer to Figure 5 and 6). The IF sig-
nal will be aliased to the ADC’s baseband region due to the
sampling process in a similar manner that a mixer will down
convert an IF signal. For signals in various Nyquist zones, the
following equation may be used to determine the final frequency
after aliasing.
f1 NYQUIST = fSIGNAL
f2 NYQUIST = fSAMPLE – fSIGNAL
f3 NYQUIST = abs (fSAMPLE – fSIGNAL)
f4 NYQUIST = 2 × fSAMPLE – fSIGNAL
f5 NYQUIST = abs (2 × fSAMPLE – fSIGNAL)
There are several potential benefits in using the ADC to alias
(i.e., mix) down a narrowband or wideband IF signal. First and
foremost is the elimination of a complete mixer stage with its
associated amplifiers and filters, reducing cost and power dissi-
pation. Second is the ability to apply various DSP techniques to
perform such functions as filtering, channel selection, quadra-
ture demodulation, data reduction, and detection.
One common example is the digitization of a 10.7 MHz IF using a
low jitter 2.5 MHz sample clock. Using the equation above for
the fifth Nyquist zone, the resultant frequency after sampling is
700 kHz. Figure 49 shows the typical performance of the
AD9243 operating under these conditions. Figure 50 demon-
strates how the AD9243 is still able to maintain a high degree of
linearity and SFDR over a wide amplitude.
0
1
–15
–30
–45
–60
–75
–90
7
4
–105
2
9
–120
–135
–150
0
1.25
FREQUENCY – MHz
Figure 49. IF Sampling a 10.7 MHz Input Using the
AD9243 (VCM = 2.5 V, Input Span = 2 V p-p)
110
100
SFDR – dBFS
90
80
70
SFDR – dBc
60
50
40
–60
–50
–40
–30
–20
–10
0
AIN – dBFS
Figure 50. AD9243 Differential Input SNR/SFDR vs.
Input Amplitude (AIN) @ 10.7 MHz
–20–
REV. A
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