• State
  • Locked Locked
  • Replies 1 reply
  • Subscribers 22 subscribers
  • Views 291 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LMX2492: ramp generation for FMCW

Kiyoyuki Ihara
Prodigy 10 points

Part Number: LMX2492

Tool/software:

Is it possible to generate FMCW waveform with LMX2492 as follows ?

- freq range : from 5300MHz to 5900MHz

- phase detector freq : 200MHz (detect cycle should be 5ns)

- sweep time : 3us

Also to achieve the above, what loop bandwidth and other design condition are appropriate ?

Then, I think the loop bandwidth should be like more than 5MHz but it looks a bit too high for usual PLL design. If so, how should the sweep time be modified ?

  • 0
    TI__Guru** 120040 points

    Hi Ihara-san,

    LMX2492 can support this operation, the linearity of the outcome, as you have mentioned, depends on the loop bandwidth. We need to use as wide loop bandwidth as possible. 

    Given the configuration you have, there are 600 ramps, each ramp needs to change the frequency by 1MHz. 

    As an example, loop bandwidth = 4.45MHz, Phase margin = 47.8deg

    Switching time from 5300MHz to 5301MHz is approx. 56ns. 

    Looks to me 3µs ramp duration is too short to be possible.