ADF4158 datasheet(28/36 Pages) AD

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ADF4158

Rev. 0 | Page 28 of 36

Delayed Start

A delayed start can be used with two different parts to control

the start time. The idea of delayed start is shown in Figure 37.

TIME

RAMP WITH

DELAYED START

RAMP WITHOUT

DELAYED START

Figure 37. Delayed Start of Sawtooth Ramp

Example

For example, to program a delayed start with two different parts

to control the start time,

Set DB15 in Register R7 to 1 to enable the delayed start of

ramp option.

Set Bit DB16 in Register R7 to 0 and the 12-bit delay start

word (DB[14:3] in Register R7) to 125 to delay the ramp on

the first part is delayed by 5 μs. The delay is calculated as

follows:

Delay = TPFD × Delay Start Word

= 40 ns × 125 = 5 μs

Set Bit DB16 in Register R7 to 1 and the 12-bit delay start

word (DB[14:3] in Register R7) to 125 to delay the ramp

on the second part is delayed by 125 μs. Use the following

formula for calculating the delay:

Delay = tPFD × MOD × Delay Start Word

= 40 ns × 25 × 125 = 125 μs

Eventually, the ramp must be activated as described in

Activating the Ramp section.

Delay Between Ramps

This feature adds a delay between bursts in ramp. Figure 38

shows a delay between ramps in sawtooth mode.

TIME

DELAY

Figure 38. Delay Between Ramps for Sawtooth Mode

Example

For example, to add a delay between bursts in a ramp,

Set DB17 in Register R7 to 1 to enable delay between

ramps option.

Set Bit DB16 in Register R7 to 0 and the 12-bit delay start

word (DB[14:3] in Register R7) to 125 to delay the ramp

by 5 μs. The delay is calculated as follows:

Delay = tPFD × Delay Start Word

= 40 ns × 125 = 5 μs

If a longer delay is needed, for example, 125 μs, Bit DB16

in Register R7 should be set to 1 and the 12-bit delay start

word (DB[14:3] in Register R7) should be set to 125. The

delay is calculated as follows

Delay = tPFD × MOD × Delay Start Word

= 40 ns × 25 × 125 = 125 μs

There is also a possibility to activate fast-lock operation for

the first period of delay. This is done by setting Bit DB18 in

mitigate the frequency overshoot on the transition from one

sawtooth to the next. Eventually, the ramp must be activated

as described in Activating the Ramp section.

Nonlinear Ramp Mode

The ADF4158 is capable of generating a parabolic ramp. The

output frequency is generated according to the following

equation:

fOUT(n + 1) = fOUT(n) + n × fDEV

(16)

where:

fOUT is output frequency.

fDEV is frequency deviation.

n is step number.

TIME

Figure 39. Parabolic Ramp

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