AD9958SLASHPCBZ datasheet(27/44 Pages) AD

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AD9958

Rev. A | Page 27 of 44

FTW0

SINGLE-TONE

MODE

LINEAR SWEEP MODE ENABLE—NO-DWELL BIT SET

FTW1

fOUT

TIME

P2 = 1

P2 = 0

P2 = 1

P2 = 0

Figure 38. Linear Sweep Mode (No-Dwell Enabled)

FTW0

SINGLE-TONE

MODE

LINEAR SWEEP MODE

AT POINT A: LOAD RISING RAMP RATE REGISTER, APPLY RDW<31:0>

AT POINT B: LOAD FALLING RAMP RATE REGISTER, APPLY FDW<31:0>

P2 = 1

P2 = 0

TIME

FTW1

fOUT

Figure 39. Linear Sweep Mode (No-Dwell 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 accumula-

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

zeroing function. CFR[4] is the autoclear sweep accumulator bit

and CFR[2] is the autoclear 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 autoclear 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 autoclear phase accumulator bit,

when set, clears and releases the phase accumulator upon an

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

clearing 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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