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(a) Complex Output in X4 and X4L Modes (b) Real Output in X4 and X4L Modes
f
SIG
/f
DAC
−0.5
−0.4
−0.3
−0.2
−0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.0 0.1 0.2 0.3 0.4 0.5
Spurious Frequency/f
DAC
G028
f
SIG
− f
DAC
*3/4
f
SIG
− f
DAC
/2
f
SIG
− f
DAC
/4
f
SIG
+ f
DAC
/4
f
SIG
f
SIG
/f
DAC
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.0 0.1 0.2 0.3 0.4 0.5
Spurious Frequency/f
DAC
G029
f
SIG
+ f
DAC
/4
f
SIG
− f
DAC
*3/4
f
SIG
− f
DAC
/4
f
SIG
f
SIG
− f
DAC
/2
(a) Complex Output in X8 Mode (b) Real Output in X8 Mode
f
SIG
/f
DAC
−0.5
−0.4
−0.3
−0.2
−0.1
−0.0
0.1
0.2
0.3
0.4
0.5
0.0 0.1 0.2 0.3 0.4 0.5
Spurious Frequency/f
DAC
G030
f
SIG
+ f
DAC
/4
f
SIG
− f
DAC
*3/4
f
SIG
− f
DAC
/4
f
SIG
− f
DAC
/2
f
SIG
− f
DAC
*7/8
f
SIG
f
SIG
− f
DAC
/8
f
SIG
+ f
DAC
/8
f
SIG
/f
DAC
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.0 0.1 0.2 0.3 0.4 0.5
Spurious Frequency/f
DAC
G031
f
SIG
− f
DAC
/4
f
SIG
− f
DAC
*7/8
f
SIG
− f
DAC
/2
f
SIG
+ f
DAC
/4
f
SIG
+ f
DAC
/8
f
SIG
f
SIG
− f
DAC
/8
f
SIG
− f
DAC
*3/4
Amplitude of the Spurious Signals
DAC5687
SLWS164E – FEBRUARY 2005 – REVISED SEPTEMBER 2006
Figure 71. Frequency of Clock Mixing Spurious Images in X4 and X4L Modes
Figure 72 shows the location of spurious signals for X8 mode as a function of f
SIG
/f
DAC
. The addition of the f
DAC
/8
clock frequency for the first interpolation filter creates four new spurious signals. For a complex output, the
nearest spurious signals are f
DAC
/8 offset from f
SIG
. For a real output, the optimum real output frequencies f
SIG
=
f
DAC
× N/16 (N = 3 and 5), where the minimum spurious product offset from f
SIG
is f
DAC
/8.
Figure 72. Frequency of Clock Mixing Spurious Images in X8 Mode
The spurious signal amplitude is sensitive to factors such as temperature, voltage, and process. The following
typical worst-case estimates to account for the variation over these factors are provided as design guidelines.
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