# How to make DDS AD9854 output Phase-Coherent ?

M

#### [email protected]

Jan 1, 1970
0
Dear all,

I am new to DDS AD9854 and was wondering if you can help me with a
specific problem not
directly solvable.

My main aim is to generate a simple chirp signal which should be Phase-
Coherent. The standard output is Phase-Continuous. Does anyone have
any suggestions how to do it ?

Many Thanks.

J

#### John O'Flaherty

Jan 1, 1970
0
Dear all,

I am new to DDS AD9854 and was wondering if you can help me with a
specific problem not
directly solvable.

My main aim is to generate a simple chirp signal which should be Phase-
Coherent. The standard output is Phase-Continuous. Does anyone have
any suggestions how to do it ?

Phase coherent with what?

M

#### [email protected]

Jan 1, 1970
0
Phase coherent with what?

Dear John,

In a chrip signal, the output goes from F1 to F2 and then back to F1
at each I/O UD pulse. I want the phase to remain the same (or zero) at
every transition from F2 to F1. This is what I mean by phase-
coherent.

Many Thanks.

J

#### John O'Flaherty

Jan 1, 1970
0
Dear John,

In a chrip signal, the output goes from F1 to F2 and then back to F1
at each I/O UD pulse. I want the phase to remain the same (or zero) at
every transition from F2 to F1. This is what I mean by phase-
coherent.

So, the phase behavior should be the same on successive chirps? It
sounds as if you would have to synchronize the pulse that starts the
transition from F1 to F2 with the state of the device, or reset the
device, and it would have to behave stably enough during the chirp to
keep the phase from deviating at F2. If you also mean that the return
from F2 to F1 must begin at zero absolute phase, then the length and
rate of change of the chirp would have to be controlled as well. I'm
not familiar with the device you mention, but logic would seem to
require synchronization.

M

#### [email protected]

Jan 1, 1970
0
So, the phase behavior should be the same on successive chirps? It
sounds as if you would have to synchronize the pulse that starts the
transition from F1 to F2 with the state of the device, or reset the
device, and it would have to behave stably enough during the chirp to
keep the phase from deviating at F2. If you also mean that the return
from F2 to F1 must begin at zero absolute phase, then the length and
rate of change of the chirp would have to be controlled as well. I'm
not familiar with the device you mention, but logic would seem to
require synchronization.

Thanks John for your help. Yes I think synchronization would be the

But instead of reseting the device everytime wouldn't clearing the
Phase Accumulator be a better option?

regards,
Farrukh

J

#### John O'Flaherty

Jan 1, 1970
0
Thanks John for your help. Yes I think synchronization would be the

But instead of reseting the device everytime wouldn't clearing the
Phase Accumulator be a better option?

As I mentioned, I'm not familiar with it. Would resetting the phase
accumulator make an instantaneous discontinuity? Does it have to run
all the time, even when it's not chirping? Maybe detecting a certain
state of the device and synchronizing the external request to that
would be better than resetting or changing it. Good luck.

J
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