LMX 2572 Ramping

Hi Gerardo,

Automatic ramp will not change the CHDIV value, so the CHDIV must be kept constant during the ramp. In your use case, CHDIV will be changing, you cannot use ramp to implement this sweep.

Gerardo,

For ramping, the first thing we should do be aware of the limitations:
1. If the ramp frequency changes too much, the VCO MUST recalibrate. The part will automatically do this if you allow it, but you need to be aware. This amount of frequency change varies with VCO frequency, but could be on the order of 10 MHz.
2. The channel divider must be manually changed.
3. The minumum VCO frequency is 3200 MHz and the maximum VCO divider is 256, so this is a minimum output frequency of 12.5 MHz, higher than 10 MHz you specify


So now choose the type of ramping. If you choose the automatic ramping, realize that the VCO will have these calibration breaks. You can set how often and how long it takes, but there is a maximum frequency change you can wait and a minimum length you can specify.

If you choose manual pin ramping, you can just use the pins to manually cause the ramp to go up and down. But as the channel divider is changing, then so is the step.

So in this case, you need to define a ramping step. But as this is defined at the VCO frequency, lets start talking about the VCO frequency. So you can ramp from 3200 to 6400 MHz at the VCO. Or if you divide by 32 it looks like 100 to 200 MHz. Whether you do manual pin ramping or automatic ramping, this VCO frequency is the same. In this case, manual pin ramping might make more sense because there is some programming in the middle. Maybe do something like this:

Set outptu divider to 256
Ramp VCO from 3200 to 6400 MHz, Output ranges from 12.5 to 25 MHz

Change outptu divider to 128
Ramp VCO from 3200 to 6400 MHz, output ranges from 25-50 MHz

...


And so on.

Hope this helps.

Regards,
Dean