AD9125 Analog Devices, AD9125 Datasheet - Page 32

• Manufacturer Part Number: AD9125
• Manufacturer: Analog Devices

Specifications of AD9125

• 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: Par

AD9125
DIGITAL DATAPATH
The block diagram in Figure 50 shows the functionality of the
digital datapath. The digital processing includes a premodulation
block, three half-band interpolation filters, a quadrature modulator
with a fine resolution NCO, a phase and offset adjustment
block, and an inverse sinc filter.
The digital datapath accepts I and Q data streams and processes
them as a quadrature data stream. The signal processing blocks can
be used when the input data stream is represented as complex data.
The datapath can be used to process an input data stream
representing two independent real data streams as well, but
the functionality is somewhat restricted. The premodulation
block can be used, as well as any of the nonshifted interpolation
filter modes (see the Premodulation section for more details).
PREMODULATION
The half-band interpolation filters have selectable pass bands
that allow the center frequencies to be moved in increments of
½ of their input data rate. The premodulation block provides a
digital upconversion of the incoming waveform by ½ of the
incoming data rate, f
baseband input data to the center of the interpolation filters’
pass band.
INTERPOLATION FILTERS
The transmit path contains three interpolation filters. Each of
the three interpolation filters provides a 2× increase in output data
rate. The half-band (HB) filters can be individually bypassed or
cascaded to provide 1×, 2×, 4×, or 8× interpolation ratios. Each
of the half-band filter stages offers a different combination of
bandwidths and operating modes.
The bandwidth of the three half-band filters with respect to the
data rate at the filter input is as follows:
•
•
•
The usable bandwidth is defined as the frequency over which
the filters have a pass-band ripple of less than ±0.001 dB and an
image rejection of greater than +85 dB. As is discussed in the
Half-Band Filter 1 (HB1) section, the image rejection usually sets
the usable bandwidth of the filter, not the pass-band flatness.
The half-band filters operate in several modes, providing
programmable pass-band center frequencies as well as signal
modulation. The HB1 filter has four modes of operation, and
the HB2 and HB3 filters each have eight modes of operation.
PREMOD
Bandwidth of HB1 = 0.8 × f
Bandwidth of HB2 = 0.5 × f
Bandwidth of HB3 = 0.4 × f
Figure 50. Block Diagram of Digital Datapath
HB1
DATA
. This can be used to frequency-shift
HB2
IN1
IN2
IN3
HB3
ADJUST
OFFSET
PHASE
AND
SINC
–1
Rev. 0 | Page 32 of 56
Half-Band Filter 1 (HB1)
HB1 has four modes of operation, as shown in Figure 51. 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 input signal is modulated by the filter.
As shown in Figure 51, the center frequency in each mode is
offset by ½ the input data rate (f
Mode 1 do not modulate the input signal. Mode 2 and Mode 3
modulate the input signal by f
and Mode 2, the I and Q paths operate independently and no
mixing of the data between channels occurs. When HB1 operates
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 16 summarizes the HB1 modes.
Table 16. HB1 Filter Mode Summary
Mode
0
1
2
3
–100
–20
–40
–60
–80
0
0
f
DC
f
f
3f
MODE 0
IN
IN
CENTER
0.2
/2
IN
/2
0.4
NORMALIZED FREQUENCY (×
Figure 51. HB1 Filter Modes
0.6
MODE 1
0.8
f
None
None
f
f
IN1
MOD
IN
IN
. When HB1 operates in Mode 0
IN1
1.0
) of the filter. Mode 0 and
MODE 2
1.2
Input Data
Real or complex
Complex
Real or complex
Complex
1.4
f
IN1
)
1.6
MODE 3
1.8
2
.0