Datasheet

AD9957 Data Sheet
Rev. C | Page 18 of 64
BLACKFIN INTERFACE (BFI) MODE
A subset of the QDUC mode is the Blackfin interface (BFI)
mode, shown in Figure 27; grayed items are inactive. In this
mode, a separate I and Q serial bit stream is applied to the
baseband data port instead of parallel data-words. The two
serial inputs provide for 16-bit I- and Q-words (unlike the
18-bit words in normal QDUC mode). The serial bit streams
are delivered to the Blackfin interface. The Blackfin interface
converts the 16-bit serial data into 16-bit parallel data to
propagate down the signal processing chain.
The Blackfin interface includes an additional pair of half-band
filters in both I and Q signal paths (not shown explicitly in the
diagram). The two half-band filters increase the interpolation
of the baseband data by a factor of four, relative to the normal
QDUC mode.
The synchronization of the serial data occurs through the
PDCLK signal. In BFI mode, the PDCLK signal is effectively
the bit clock for the serial data.
Note that the system clock is limited to 750 MHz in BFI mode.
06384-007
PDCLK
I/Q IN
EXT_PWR_DWN
DAC_RSET
IOUT
IOUT
TxENABLE
DAC GAIN
θ
INVERSE
SINC
FILTER
CLOCK
FTW
PW
8
SYSCLK
PLL
÷2
CLOCK MODE
REF_CLK
REF_CLK
REFCLK_OUT
XTAL_SEL
AD9957
ω
cos (ωt+θ)
sin (ωt+θ)
SYNC_OUT
SYNC_IN
PLL_LOCK
PLL_LOOP_FILTER
MASTER_RESET
2
2
OSK
DDS
AUX
DAC
8-BIT
POWER
DOWN
CONTROL
2
DATA ASSEMBLER AND FORMATTER
I
Q
IS
QS
BLACKFIN INTERFACE
18
18
16
16
INVERSE
CCI
INVERSE
CCI
OSK
INTERNAL CLOCK TIMING AND CONTROL
DAC
14-BIT
CCI_OVFL
OSK
FTW
PW
PARALLEL DATA
TIMING AND CONTROL
RT
RAM
PROFILE
SERIAL I/O
PORT
I/O_UPDATE
PROGRAMMING
REGISTERS
3
I Q IS QS
HALF-BAND
FILTERS (4×)
CCI
(1× TO 63×)
HALF-BAND
FILTERS (4×)
CCI
(1× TO 63×)
OUTPUT
SCALE
FACTOR
SDIO
CS
I/O_RESET
SCLK
SDO
Figure 27. Quadrature Modulation Mode, Blackfin Interface