AD9879BS Analog Devices Inc, AD9879BS Datasheet - Page 22

• Manufacturer Part Number: AD9879BS
• Description: IC FRONT-END MIXED-SGNL 100-MQFP
• Manufacturer: Analog Devices Inc

Specifications of AD9879BS

• Rohs Status: RoHS non-compliant
• Number Of Bits: 12
• Number Of Channels: 5
• Power (watts): 587mW
• Voltage - Supply, Analog: 3.3V
• Voltage - Supply, Digital: 3.3V
• Package / Case: 100-MQFP, 100-PQFP

AD9879
TRANSMIT PATH (TX)
TRANSMIT TIMING
The AD9879 provides a master clock, MCLK, and expects 6-bit
multiplexed TxIQ data upon each rising edge. Transmit
symbols are framed with the TxSYNC input. TxSYNC high
indicates the start of a transmit symbol. Four consecutive 6-bit
data packages form a symbol (I MSB, I LSB, Q MSB, and Q LSB).
DATA ASSEMBLER
The input data stream is representative complex data. Two 6-bit
words form a 12-bit symbol component (in twos complement
format). Four input samples are required to produce one I/Q
data pair. The I/Q sample rate, f
half-band filter is a quarter of the input data rate, f
The I/Q sample rate, f
maximum transmit spectrum. This is the familiar Nyquist limit
and is equal to one-half f
HALF-BAND FILTERS (HBFs)
HBF 1 and HBF 2 are both interpolating filters, each of which
doubles the sampling rate. Together, HBF 1 and HBF 2 have
26 taps and provide a factor-of-four increase in the sampling
rate (4 × f
In relation to phase response, both HBFs are linear phase filters.
As such, virtually no phase distortion is introduced within the
pass band of the filters. This is an important feature, because
phase distortion is generally intolerable in a data transmission
system.
IQCLK
TXSYNC
or 8 × f
MCLK
TXIQ
IQCLK
NYQ
IQCLK
).
, puts a bandwidth limit on the
TXI[11:6]
, hereafter referred to as f
IQCLK
, at the input to the first
TXI[5:0]
TXQ[11:6]
MCLK
.
NYQ
TXQ[5:0]
Figure 14. Transmit Path Timing
.
Rev. A | Page 22 of 32
TXI[11:6]
t
SU
TXI[5:0]
CASCADED INTEGRATOR-COMB (CIC) FILTER
The CIC filter is configured as a programmable interpolator
and provides a sample rate increase by a factor of 4. The
frequency response of the CIC filter is given by
The frequency response in this form has f scaled to the output
sample rate of the CIC filter. That is, f = 1 corresponds to the
frequency of the output sample rate of the CIC filter. H(f/R)
yields the frequency response with respect to the input sample
of the CIC filter.
COMBINED FILTER RESPONSE
The combined frequency response of HBF 1, HBF 2, and
CIC puts a limit on the input signal bandwidth that can be
propagated through the AD9879.
The usable bandwidth of the filter chain puts a limit on the
maximum data rate that can be propagated through the
AD9879. A look at the pass-band detail of the combined filter
response (Figure 15 and Figure 16) indicates that to maintain an
amplitude error of no more than 1 dB, signals are restricted to a
bandwidth of no more than approximately 60% of f
t
HD
H(f)
TXQ[11:6]
=
⎡
⎢
⎣
⎛
⎜
⎝
1
4
⎞
⎟
⎠
TXQ[5:0]
1
−
1
e
−
−
e
j
(
j(
2π
2π
f
TXI[11:6]
( )
f)
4
)
⎤
⎥
⎦
3
=
⎡
⎢
⎣
⎛
⎜
⎝
TXI[5:0]
1
4
⎞
⎟
⎠
sin
sin
(
( )
4π
π
f
f
)
⎤
⎥
⎦
3
NYQ
.
(15)