AD9958SLASHPCB datasheet(25/40 Pages) AD

25 / 40 page

AD9958

Rev. 0 | Page 25 of 40

FTW0

SINGLE–TONE

MODE

LINEAR SWEEP MODE ENABLE, NO-DWELL BIT SET

FTW1

FOUT

TIME

PS<2> = 1 PS<2> = 0

PS<2> = 0

PS<2> = 1

PS<2> = 0

Figure 37.

FTW0

SINGLE–TONE

MODE

LINEAR SWEEP MODE

AT POINT A: LOAD RISING RAMP RATE REGISTER, APPLY RISING DFTW.

AT POINT B: LOAD FALLING RAMP RATE REGISTER, APPLY FALLING DFTW.

PS<2> = 1

PS<2> = 0

TIME

FTW1

FOUT

Figure 38. Linear Sweep with the No-Dwell Feature Disabled

SWEEP AND PHASE ACCUMULATOR CLEARING

FUNCTIONS

The AD9958 allows two different clearing functions. The first

is a continuous zeroing of the sweep logic and phase accumu-

lator (clear and hold). The second is a clear and release or

automatic zeroing function. CFR <4> is the automatic clear

sweep accumulator bit and CFR <2> is the automatic clear

phase accumulator bit. The continuous clear bits are located in

CFR, where CFR <3> clears the sweep accumulator and

CFR <1> clears the phase accumulator.

Continuous Clear Bits

The continuous clear bits are static control signals that, when

active high, hold the respective accumulator at 0 while the bit is

active. When the bit goes low, the respective accumulator is

allowed to operate.

Clear and Release Bits

The auto clear sweep accumulator bit, when set, clears and

releases the sweep accumulator upon an I/O update or a change

in the profile input pins. The auto clear phase accumulator,

when set, clears and releases the phase accumulator upon an

I/O update or a change in the profile pins. The automatic clear-

ing function is repeated for every subsequent I/O update or

change in profile pins until the clear and release bits are reset

via the serial port.

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