Datasheet

ADF4159 Data Sheet
Rev. D | Page 30 of 36
Delay Between Ramps
The ADF4159 can be configured to add a delay between bursts in
ramps. Figure 42, Figure 43, and Figure 44 show a delay between
ramps in sawtooth, triangular, and clipped triangular mode,
respectively.
FREQUENCY
DELAY
TIME
10849-035
Figure 42. Delay Between Ramps for Sawtooth Mode
FREQUENCY
TIME
10849-036
Figure 43. Delay Between Ramps for Triangular Mode
FREQUENCY
TIME
DELAY
10849-037
Figure 44. Delay Between Ramps for Clipped Triangular Mode
Example
For example, to add a delay between bursts in a ramp, follow
these steps:
1. Enable the delay between ramps option by setting Bit DB17
in Register R7 to 1.
2. Delay the ramp by 5 µs by setting Bit DB16 in Register R7
to 0 and setting the 12-bit delay start word (Bits DB[14:3] in
Register R7) to 125 (f
PFD
= 25 MHz). The delay is calculated
as follows:
Delay = t
PFD
× Delay Start Word
Delay = 40 ns × 125 = 5 µs
If a longer delay is needed, for example, 125 µs, set Bit DB16 in
Register R7 to 1, and set the 12-bit delay start word (Bits DB[14:3]
in Register R7) to 125. The delay is calculated as follows:
Delay = t
PFD
× CLK
1
× Delay Start Word
Delay = 40 ns × 25 × 125 = 125 µs
It is also possible to activate fast lock operation for the first
period of delay by setting Bit DB18 in Register R7 to 1. This
feature is useful for sawtooth ramps to mitigate the frequency
overshoot on the transition from one sawtooth to the next.
To activate the ramp, see the Activating the Ramp section.
Dual Ramp Rates Mode with Delay
This mode combines the modes described in the Dual Ramps
with Different Ramp Rates section and the Delay Between
Ramps section (see Figure 45).
10849-140
TIME
FREQUENCY
Figure 45. Dual Ramp Rates Mode with Delay
To enable this configuration,
1. Program the two ramp rates mode as described in the
Dual Ramps with Different Ramp Rates section.
2. Program the delay as described in the Delay Between
Ramps section.
Parabolic (Nonlinear) Ramp Mode
The ADF4159 is capable of generating a parabolic ramp (see
Figure 46).
FREQUENCY
TI
ME
10849-141
Figure 46. Parabolic Ramp
The output frequency is generated according to the following
equation:
f
OUT
(n + 1) = f
OUT
(n) + n × f
DEV
(14)
where:
f
OUT
is the output frequency.
n is the step number.
f
DEV
is the frequency deviation.
Example
This example describes how to set up and use the parabolic ramp
mode with the following parameters:
• f
OUT
= 5790 MHz
• f
DEV
= 100 kHz
• Number of steps = 50
• Duration of a single step = 10 µs