AD9852ASQZ datasheet(19/52 Pages) AD

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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

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.

Figure 34 and Figure 35 graphically depict the frequency vs.

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.

FREQUENCY

MODE

TW1

TW2

FSK DATA (PIN 29)

001 (FSK NO RAMP)

000 (DEFAULT)

I/O UD CLK

Figure 33. Unramped (Traditional) FSK Mode

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