Datasheet

AD9957 Data Sheet
Rev. C | Page 16 of 64
MODES OF OPERATION
OVERVIEW
The AD9957 has three basic operating modes.
• Quadrature modulation (QDUC) mode (default)
• Interpolating DAC mode
• Single tone mode
The active mode is selected via the operating mode bits in
Control Function Register 1 (CFR1). Single tone mode allows
the device to operate as a sinusoidal generator with the DDS
driving the DAC directly.
Interpolating DAC mode bypasses the DDS, allowing the user
to deliver baseband data to the device at a sample rate lower
than that of the DAC. An internal chain of rate interpolation
filters the user data and upsamples to the DAC sample rate.
Combined, the filters provide for programmable rate interpola-
tion while suppressing spectral images and retaining the original
baseband spectrum.
QDUC mode employs both the DDS and the rate interpolation
filters. In this case, two parallel banks of rate interpolation
filters allow baseband processing of in-phase and quadrature
(I/Q) signals with the DDS providing the carrier signal to be
modulated by the baseband signals. A detailed block diagram of
the AD9957 is shown in Figure 25.
The inverse sinc filter is available in all three modes.
06384-005
PDCLK
I/Q IN
EXT_PWR_DWN
DAC_RSET
IOUT
IOUT
TxENABLE
FTW
PW
DAC GAIN
θ
INVERSE
SINC
FILTER
CLOCK
FTW
PW
8
SYSCLK
PLL
÷2
CLOCK MODE
REF_CLK
REF_CLK
REFCLK_OUT
XTAL_SEL
PARALLEL DATA
TIMING AND CONTROL
AD9957
ω
cos (ωt+θ)
sin (ωt+θ)
SYNC_OUT
SYNC_IN
PLL_LOCK
PLL_LOOP_FILTER
MASTER_RESET
2
2
CCI_OVFL
OSK
DDS
AUX
DAC
8-BIT
POWER
DOWN
CONTROL
RT
RAM
PROFILE
SERIAL I/O
PORT
I/O_UPDATE
PROGRAMMING
REGISTERS
3
I Q IS QS
18
DATA ASSEMBLER AND FORMATTER
I
Q
IS
QS
BLACKFIN INTERFACE
18
18
16
16
HALF-BAND
FILTERS (4×)
INVERSE
CCI
CCI
(1× TO 63×)
HALF-BAND
FILTERS (4×)
INVERSE
CCI
CCI
(1× TO 63×)
OSK
INTERNAL CLOCK TIMING AND CONTROL
DAC
14-BIT
OUTPUT
SCALE
FACTOR
SDIO
CS
I/O_RESET
SCLK
SDO
Figure 25. Detailed Block Diagram