Evaluation Board
User Guide
UG-XXX
Rev. A | Page 11 of 14
DIGITAL RAMP GENERATOR (DRG)
Figure 12. Digital Ramp Generator Window
Digital Ramp Generator is synonymous to linear sweep. The
ramp generation parameters allow the user to control both the
rising and falling slopes of the ramp, the upper and lower
boundaries of the ramp, the step size and step rate of the rising
portion of the ramp, and the step size and step rate of the falling
portion of the ramp. This is digitally generated with a 32-bit
output resolution that can be programmed to represent
frequency, phase, or amplitude. Refer to AD9915 datasheet for
more information on DRG.
There are three general parameters that a DRG requires: region
for the linear sweep, step size, and step rate. In order to specify
the region, two values must be chosen (Sweep 0 and Sweep 1
wherein each contains a different representation, depending on
the mode; MHz for frequency, degree for phase, and a scalar
value for amplitude) and it must be within the allowable range.
Step size indicates the value that would be incremented while
step rate determines the time interval/period for that increment
(in µs).
To use the digital ramp generator (DRG) function of the
AD9915, select the
Enable Digital Ramp Generator
checkbox. Under
Mode
section, select the parameter to be
generated –frequency, phase, or amplitude. In the
Settings
section, The
Auto Clear Digital Ramp Accumulator
checkbox allows you to set the clear digital ramp accumulator
bit when the I/O update signal is applied or when there is a
profile change. The clear bit is then released.
The
Clear Digital Ramp Accumulator
checkbox allows you
to set and keep the digital ramp accumulator cleared until that
bit is cleared. The
Load DRR @I/O Update
checkbox allows
you to reload the digital ramp rate when an I/O update is issued
or when there is a profile change.
Sweep Frequency 0
and
Sweep Frequency 1
are the starting
and stopping frequencies of the ramp, respectively. Note that
this is frequency, phase, or amplitude depending on which ramp
generator is selected. It is important that the value in the Sweep
0 register is always less than the value in the Sweep 1 register.
