Hi Keysight,
I have a question on the ALC/Power search feature. We've been having some trouble with narrow, pulsed signals after installing a f/w update on our sig gen's. This datasheet sets the min p/w with ALC at 1 microsecond. My question is, do the power search and ALC features require some sort of settling time? Are there any preconditions we have to take into account before providing our UUT the pulse? Another question is, if we set the power accurately in CW and then switch to pulse, how critical is ALC or power search?
D's F/W: C.06.21
C's F/W: C.03.23
Hi,
The ALC can work with pulses as narrow as 1 us. Power search disables the pulse modulation and enables the ALC. Both cases require a certain amount of time to reach the desired level. If this time is 1 ms, then it would take one thousand 1 us pulses to reach the desired level.The settling time is dependent on two things:
1.) The difference between the current level and the desired level
2.) The ALC bandwidth. (100 Hz, 1 kHz, 10 kHz, 100 kHz)
Setting the ALC bandwidth to the largest value, 100 kHz, will reduce the time required to reach the desired level.
I'm not exactly sure why a firmware upgrade would change this behavior but it is definitely possible. It may have to do with improved calibration routines or leveling algorithms. It might be possible that the firmware upgrade reset the ALC bandwidth to a value narrower than what you were using.
If you set the power in CW mode you have probably already provided the ALC enough time to level.
NOTE: I don't remember if the RF output must be on for the ALC to level.
Enabling pulse modulation without changing the RF Amplitude should have the instrument at the correct level and the pulses will be at the desired level with no waiting.
Keeping the ALC enabled, even with pulsed signals, means you are less susceptible to long term amplitude drift.
Changing the RF Amplitude while generating pulsed signals will require a certain amount of time (number of pulses) to reach each new level assuming the ALC is on.
Hope this helps
Pete