AD9148 Analog Devices, AD9148 Datasheet - Page 54

• Manufacturer Part Number: AD9148
• Manufacturer: Analog Devices

Specifications of AD9148

• Resolution (bits): 16bit
• Dac Update Rate: 1GSPS
• Dac Settling Time: n/a
• Max Pos Supply (v): +3.47V
• Single-supply: No
• Dac Type: Current Out
• Dac Input Format: LVDS,Par

AD9148
Figure 69 shows the pass-band filter response for HB3. In most
applications, the usable bandwidth of the filter is limited by the
image suppression provided by the stop-band rejection and not
by the pass-band flatness. Table 24 shows the pass-band flatness
and stop-band rejection the HB3 filter supports at different
bandwidths.
Table 24. HB3 Pass-Band and Stop-Band Performance by
Bandwidth
Bandwidth (% of f
40
40.8
42.4
45.6
49.8
55.6
The maximum bandwidth can be achieved if the signal carrier
frequency is placed directly at the center of one of the filter
pass bands. In this case, the entire quadrature bandwidth of the
interpolation filter (0.8 × f
bandwidth decreases as the carrier frequency of the signal moves
away from the center frequency of the filter. The worst-case
carrier frequency is one that falls directly between the center
frequency of two adjacent filters. Figure 70 shows how the
signal bandwidth changes as a function of placement in the
spectrum and interpolation rate.
–0.02
–0.04
–0.06
–0.08
–0.10
0.02
0
0
0.04
Figure 69. Pass-Band Detail of HB3
IN3
)
0.08
DATA
Pass-Band
Flatness (dB)
0.001
0.0014
0.002
0.0093
0.03
0.1
0.12
) is available. The available signal
(×
f
IN3
0.16
)
0.20
Stop-Band
Rejection (dB)
85
80
70
60
50
40
0.24
0.28
Rev. B | Page 54 of 72
FINE MODULATION
The fine modulation makes use of a numerically controlled oscillator,
a phase shifter, and a complex modulator to provide a means for
modulating the signal by a programmable carrier signal. A block
diagram of the fine modulator is shown in Figure 71. The fine
modulator allows the signal to be placed anywhere in the output
spectrum with very fine frequency resolution.
Q DATA
The quadrature modulator is used to mix the carrier signal
generated by the NCO with the I and Q signal. The NCO produces
a quadrature carrier signal to translate the input signal to a new
center frequency. A complex carrier signal is a pair of sinusoidal
waveforms of the same frequency, offset 90° from each other. The
frequency of the complex carrier signal is set via the FTW[31:0]
value in Register 0x54 through Register 0x57.
The NCO operating frequency, f
frequency of the complex carrier signal can be set from dc up
to f
The generated quadrature carrier signal is mixed with the I and Q
data. The quadrature products are then summed into the I and
Q data paths, as shown in Figure 71.
I DATA
Figure 70. Complex Signal Bandwidth as a Function of Output Frequency
0.4
0.3
0.2
0.1
DAC
0
–1/2
NCO PHASE OFFSET
FTW
/2. The frequency tuning word (FTW) is calculated as
–3/8
INTERPOLATION
WORD [15:0]
INTERPOLATION

FTW[31:0]
f
CENTER
Figure 71. Fine Modulator Block Diagram
f
–1/4
DAC
INVERSION
SPECTRAL
CARRIER FREQUENCY

–1/8
2
32
–1
DC
COSINE
NCO
SINE
NCO
0
1/8
, is at the DAC rate. The
1
1/4
3/8
–
Data Sheet
+
1/2
0.15
0.075
0.0375
×2 MODE
×4 MODE
×8 MODE
f
C
(×
OUT_I
OUT_Q
f
DAC
)