AD9852
Rev. E | Page 19 of 52
Table 7. Function Availability vs. Mode of Operation
Function
Single-Tone Mode
FSK Mode
Ramped FSK Mode
Chirp Mode
BPSK Mode
Phase Adjust 1
●
Phase Adjust 2
●
Single-Pin FSK/BPSK or HOLD
●
Single-Pin Output Shaped Keying
●
Phase Offset or Modulation
●
Amplitude Control or Modulation
●
Inverse Sinc Filter
●
Frequency Tuning Word 1
●
Frequency Tuning Word 2
●
Automatic Frequency Sweep
●
UNRAMPED FSK (MODE 001)
When this mode is selected, the output frequency of the DDS is
a function of the values loaded into Frequency Tuning Word
Register 1 and Frequency Tuning Word Register 2 and the logic
level of Pin 29 (FSK/BPSK/HOLD). A logic low on Pin 29
chooses F1 (Frequency Tuning Word 1, Parallel Address 4 hex
to Parallel Address 9 hex), and a logic high chooses F2
(Frequency Tuning Word 2, Parallel Register Address A hex to
Parallel Register Address F hex). Changes in frequency are
phase continuous and are internally coincident with the FSK
data pin (Pin 29); however, there is deterministic pipeline delay
between the FSK data signal and the DAC output (see
Table 1).
The unramped FSK mode (see
Figure 33) is representative
of traditional FSK, radio teletype (RTTY), or teletype (TTY)
transmission of digital data. FSK is a very reliable means of
digital communication; however, it makes inefficient use of
the bandwidth in the RF spectrum. Ramped FSK, shown in
Figure 34, is a method of conserving the bandwidth.
RAMPED FSK (MODE 010)
In this method of FSK, changes from F1 to F2 are not
instantaneous, but are accomplished in a frequency sweep or
ramped fashion. The ramped notation implies the sweep is
linear. Although linear sweeping, or frequency ramping, is
easily and automatically accomplished, it is only one of many
possibilities. Other frequency transition schemes can be
implemented by changing the ramp rate and ramp step size at
any time during operation.
Frequency ramping, whether linear or nonlinear, necessitates
that many intermediate frequencies between F1 and F2 are
output in addition to the primary F1 and F2 frequencies.
time characteristics of a linear ramped FSK signal.
In ramped FSK mode, the delta frequency word (DFW) is
required to be programmed as a positive twos complement
value. Another requirement is that the lowest frequency (F1) be
programmed in the Frequency Tuning Word 1 registers.
F1
F2
0
FREQUENCY
MODE
TW1
TW2
FSK DATA (PIN 29)
001 (FSK NO RAMP)
F1
F2
000 (DEFAULT)
0
I/O UD CLK
00634-033
Figure 33. Unramped (Traditional) FSK Mode