LMX2594: 500MHz wide ramp generation

Alexey Faynburd

Part Number: LMX2594
Other Parts Discussed in Thread: LMX2492

Tool/software:

Hi,

I need to generate a continuous ramp for 10-10.5 GHz range with 100us period.

As far as I understand from the datasheet and these forums, the LMX2594 is not up to the task as its slew rate is much slower. I've seen a recommendation to use LMX2492 + external VCO.

What I fail to understand is why. What is the advantage of an external VCO that it will work when an internal won't? I cannot see any apparent difference. And maybe without that understanding I can choose the VCO poorly.

Thanks.

8 months ago

0 Noel Fung 8 months ago

TI__Guru** 111340 points

Hi Alexey,

There are 7 VCO cores in the chip, each core covers approx. 1GHz tuning range. This 1GHz range is divided into approx. 190 sub-band. We need calibration to pick the right VCO core and the right sub-band for a particular VCO frequency.

Your required ramp range is 500MHz. Multiple calibrations are required during the ramp period in order to maintain lock. In other words, linear ramp is not possible. LMX2594 can support linear ramp for approx. 100MHz ramp range.

If you need 500MHz linear ramp, you need discrete PLL + VCO solution.

0 Alexey Faynburd 8 months ago in reply to Noel Fung

Prodigy 30 points

Hi Noel, why an external VCO won't have this problem?

Will any VCO do or there is a specific property to look for?

0 Noel Fung 8 months ago in reply to Alexey Faynburd

TI__Guru** 111340 points

Hi Alexey,

If you pick a VCO that cover 10GHz to 10.5GHz, you can use a PLL (such as LMX2492) to implement linear frequency ramp.

Clock & timing

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LMX2594: 500MHz wide ramp generation