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AD9852

–17–

REV. 0

Single-Tone (Mode 000)

This is the default mode when master reset is asserted or when

it is user-programmed into the control register. The Phase

Accumulator, responsible for generating an output frequency, is

presented with a 48-bit value from Frequency Tuning Word 1

registers whose default values are zero. Default values from the

remaining applicable registers will further deﬁne the single-tone

output signal qualities.

The default values after a master reset, deﬁne a safe, “no output”

value resulting in an output signal of 0 Hertz, 0 phase. Upon

power-up and reset the output from both I and Q DACs will be

a dc value equal to the midscale output current. This is the

default mode amplitude setting of zero. Refer to the digital multi-

plier section for further explanation of the output amplitude

control. It will be necessary to program all or some of the 28

program registers to realize a user-deﬁned output signal.

Figure 35 graphically shows the transition from the default con-

dition (0 Hz) to a user-deﬁned output frequency (F1).

As with all Analog Devices DDSs, the value of the frequency

tuning word is determined using the following equation:

FTW = (Desired Output Frequency

× 2N)/SYSCLK.

000 (SINGLE TONE)

MODE

TW1

000 (DEFAULT)

Figure 35. Default State to User-Deﬁned Output Transition

Where N is the phase accumulator resolution (48 bits in this

instance), frequency is expressed in Hertz, and the FTW,

Frequency Tuning Word, is a decimal number. Once a decimal

number has been calculated, it must be rounded to an integer

and then converted to binary format—a series of 48 binary-

weighted 1s or 0s. The fundamental sine wave DAC output

frequency range is from dc to 1/2 SYSCLK.

Changes in frequency are phase continuous—that is, the new

frequency uses the last phase of the old frequency as the reference

point to compute the ﬁrst new frequency phase.

The single-tone mode allows the user to control the following

signal qualities:

• Output Frequency to 48-Bit Accuracy

• Output Amplitude to 12-Bit Accuracy

– Fixed, User-Deﬁned, Amplitude Control

– Variable, Programmable Amplitude Control

– Automatic, Programmable, Single-Pin-Controlled, “Shaped

On/Off Keying”

• Output Phase to 14-Bit Accuracy

Furthermore, all of these qualities can be changed or modulated

via the 8-bit parallel programming port at a 100 MHz parallel-byte

rate, or at a 10 MHz serial rate. Incorporating this attribute will

permit FM, AM, PM, FSK, PSK, ASK operation in the single-

tone mode.

Table III. Function Availability vs. Mode of Operation

Single-Pin

Phase

Amplitude

Inverse

Frequency Frequency Automatic

Phase

FSK/BPSK

Shaped-

Offset or

Control or

SINC

Tuning

Frequency

Mode

Adjust 1

Adjust 2

or HOLD

Keying

Modulation

Filter

Word 1

Word 2

Sweep

Single-Tone

FSK

Ramped FSK

CHIRP

BPSK

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