AD9148BPCZ AD [Analog Devices], AD9148BPCZ Datasheet - Page 54

• Manufacturer Part Number: AD9148BPCZ
• Description: Quad 16-Bit,1 GSPS, TxDAC+ Digital-to-Analog Converter
• Manufacturer: AD [Analog Devices]

AD9148
Figure 68 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 23 shows the pass-band flatness
and stop-band rejection the HB3 filter supports at different
bandwidths.
Table 23. 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 69 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 68. 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. PrA | Page 54 of 73
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 70. 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.
I DATA
Figure 69. Complex Signal Bandwidth as a Function of Output Frequency
0.4
0.3
0.2
0.1
0
–1/2
NCO PHASE OFFSET
–3/8
INTERPOLATION
WORD [15:0]
INTERPOLATION
FTW[31:0]
Figure 70. Fine Modulator Block Diagram
–1/4
INVERSION
SPECTRAL
Preliminary Technical Data
CARRIER FREQUENCY
–1/8
–1
DC
COSINE
NCO
SINE
0
1/8
1
1/4
3/8
–
+
1/2
0.15
0.075
0.0375
×2 MODE
×4 MODE
×8 MODE
f
C
(×
OUT_I
OUT_Q
f
DAC
)