AD9954SLASHPCB datasheet(26/36 Pages) AD

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AD9954

Rev. 0 | Page 26 of 36

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<0> = 1

PS<0> = 0

TIME

FTW1

FOUT

Figure 20. Linear Sweep Frequency Plan

FTW0

SINGLE–TONE

MODE

LINEAR SWEEP MODE ENABLE–NO DWELL BIT SET

FTW1

FOUT

TIME

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

PS<0> = 0

PS<0> = 1

PS<0> = 0

Figure 21. Linear Sweep Using No Dwell Frequency Plan

Linear Sweep No Dwell Feature

The linear sweep function can be operated with a no dwell fea-

ture. If the linear sweep no dwell bit is set, CFR1<2> = 1, the

rising sweep is started in an identical manner to the non-no

dwell linear sweep mode. Upon detecting a rising edge on the

PS<0> input pin, the rising sweep action is initiated. The fre-

quency continues to sweep up at the rate set by the rising sweep

ramp rate at the resolution set by the rising delta frequency

tuning word until it reaches the terminal frequency. Upon

reaching the terminal frequency, the output frequency immedi-

ately returns to the starting frequency and remains at the start-

ing frequency until the device detects a subsequent rising edge

on the PS<0> pin. Figure 21 is an example of the linear sweep

mode operation when the linear sweep no dwell bit is set. The

points labeled A indicate where a rising edge on PS0 is detected;

the points labeled B indicate where the AD9954 has determined

FOUT has reached the terminal frequency and automatically

returns to the starting frequency. Note that in this mode, each

sweep will require a separate rising edge on the Profile <0> pin.

Linear sweeps using the no-dwell bit can only be swept from

FTW0 to FTW1 using the positive linear sweep control word.

Toggling the PS<0> from 1 to 0 will not initiate a falling sweep

when the no dwell bit is set, nor will it interrupt a positive

sweep already underway.

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