Datasheet
AD9148 Data Sheet
Rev. B | Page 52 of 72
Half-Band Filter 1 (HB1)
HB1 has four modes of operation, as shown in Figure 64. The
shape of the filter response is identical in each of the four modes.
The four modes are distinguished by two factors: the filter center
frequency and whether the filter modulates the input signal.
0
–20
–40
–60
–80
–100
0 2.01.81.61.41.2
1.00.80.60.40.2
MAGNITUDE (dB)
(×
f
IN1
)
MODE 0
MODE 1 MODE 3
MODE 2
08910-063
Figure 64. HB1 Filter Modes
As is shown in Figure 64, the center frequency in each mode is
offset by ½ of the input data rate (f
IN1
) of the filter. Mode 0 and
Mode 1 do not modulate the input signal. Mode 2 and Mode 3
modulate the input signal by f
IN1
. When operating in Mode 0
and Mode 2, the I and Q paths operate independently and no
mixing of the data between channels occurs. When operating
in Mode 1 and Mode 3, mixing of the data between the I and Q
paths occurs; therefore, the data input into the filter is assumed
complex. Table 19 summarizes the HB1 modes.
Table 19. 2× Interpolation Filter Modes (Register 0x1C to
Register 0x1E)
Interpolation
Factor
Filter Modes
f
CENTER
(f
DAC
)
Pre-Mod HB1 HB2 HB3
2
0
0
Off
Off
0
2 1 1 Off Off f
DAC
/4
2 0 2 Off Off f
DAC
/2
2 1 3 Off Off −f
DAC
/4
Figure 65 shows the pass-band filter response for HB1. 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 20 shows the pass-band flatness
and stop-band rejection the HB1 filter supports at different
bandwidths.
0.02
–0.10
–0.08
–0.06
–0.04
–0.02
0
0 0.400.360.320.280.240.200.160.120.080.04
MAGNITUDE (dB)
(×
f
IN1
)
08910-064
Figure 65. Pass-Band Detail of HB1
Table 20. HB1 Pass-Band and Stop-Band Performance by
Bandwidth
Bandwidth (% of f
IN1
)
Pass-Band
Flatness (dB)
Stop-Band
Rejection (dB)
80 0.001 85
80.4 0.0012 80
81.2 0.0033 70
82.0 0.0076 60
83.6
0.0271
50
85.6 0.1096 40
Half-Band Filter 2 (HB2)
HB2 has eight modes of operation, as shown in Figure 66 and
Figure 67. The shape of the filter response is identical in each of
the eight modes. The eight modes are distinguished by two factors,
the filter center frequency and whether the input signal is
modulated by the filter.
0
–20
–40
–60
–80
–100
0 2.01.81.61.41.21.00.80.60.40.2
MAGNITUDE (dB)
(× f
IN2
)
MODE 0
MODE 2 MODE 6
MODE 4
08910-065
Figure 66. HB2, Even Filter Modes