Datasheet
AD9122
Rev. B | Page 40 of 60
The available signal bandwidth for 8× interpolation vs. output
frequency varies between 50% and 80% of the input data rate,
as shown in Figure 59. Note that in 8× interpolation mode,
f
DAC
= 8 × f
DATA
; therefore, the data shown in Figure 59 repeats
eight times from dc to f
DAC
.
HB1, HB2, AND HB3
f
OUT
/f
DATA
BANDWIDTH/f
DATA
0.25
0.8
0.6
0.5
1.000.750.50
0.1 0.90.60.4
08281-029
Figure 59. Signal Bandwidth vs. Center Frequency of the Output Signal,
8× Interpolation
DETERMINING INTERPOLATION FILTER MODES
Table 20 shows the recommended interpolation filter settings
for a variety of filter interpolation factors, filter center frequencies,
and signal modulation. The interpolation modes were chosen
based on the final center frequency of the signal and by deter-
mining the frequency shift of the signal required. When these
parameters are known and put in terms of the input data rate
(f
DATA
), the filter configuration that comes closest to matching
is selected from Table 20.
Table 20. Recommended Interpolation Filter Modes (Register 0x1C Through Register 0x1E)
Filter Modes
Interpolation Factor HB1[1:0] HB2[5:0] HB3[5:0] f
SIGNAL
Modulation f
CENTER
Shift
8 00 (Mode 0) 000000 000000 DC 0
8 01 (Mode 1) 001001 000000 DC
1
f
DATA
/2
8
2
10 (Mode 2) 010010 001001 f
DATA
f
DATA
8 11 (Mode 3) 011011 001001 f
DATA
1
3f
DATA
/2
8 00 (Mode 0) 100100 010010 2f
DATA
2f
DATA
8 01 (Mode 1) 101101 010010 2f
DATA
1
5f
DATA
/2
8 10 (Mode 2) 110110 011011 3f
DATA
3f
DATA
8 11 (Mode 3) 111111 011011 3f
DATA
1
7f
DATA
/2
8 00 (Mode 0) 000000 100100 4f
DATA
4f
DATA
8 01 (Mode 1) 001001 100100 4f
DATA
1
9f
DATA
/2
8 10 (Mode 2) 010010 101101 5f
DATA
5f
DATA
8 11 (Mode 3) 011011 101101 5f
DATA
1
11f
DATA
/2
8 00 (Mode 0) 100100 110110 6f
DATA
6f
DATA
8 01 (Mode 1) 101101 110110 6f
DATA
1
13f
DATA
/2
8 10 (Mode 2) 110110 111111 7f
DATA
7f
DATA
8 11 (Mode 3) 111111 111111 7f
DATA
1
15f
DATA
/2
4 00 (Mode 0) 000000 Bypass DC 0
4
3
01 (Mode 1) 001001 Bypass DC
1
f
DATA
/2
4 10 (Mode 2) 010010 Bypass f
DATA
f
DATA
4 11 (Mode 3) 011011 Bypass f
DATA
1
3f
DATA
/2
4 00 (Mode 0) 100100 Bypass 2f
DATA
2f
DATA
4 01 (Mode 1) 101101 Bypass 2f
DATA
1
5f
DATA
/2
4 10 (Mode 2) 110110 Bypass 3f
DATA
3f
DATA
4 11 (Mode 3) 111111 Bypass 3f
DATA
1
7f
DATA
/2
2 00 (Mode 0) Bypass Bypass DC 0
2 01 (Mode 1) Bypass Bypass DC
1
f
DATA
/2
2 10 (Mode 2) Bypass Bypass f
DATA
f
DATA
2 11 (Mode 3) Bypass Bypass f
DATA
1
3f
DATA
/2
1
When HB1 Mode 1 or Mode 3 is used, enabling premodulation provides an additional frequency translation of the input signal by f
DATA
/2, which centers a baseband
input signal in the filter pass band.
2
This configuration was used in the 8× interpolation without NCO example (see the 8× Interpolation Without NCO section).
3
This configuration was used in the 4× interpolation with NCO example (see the 4× Interpolation with NCO section).