LMX2820: Related to frequency hopping

shivakant dwivedi

Prodigy 10 points

Part Number: LMX2820

Hi team,

Can you know the max & min frequency hopping time LMX2820 can support.

How fast it can do frequency hopping?

Is there any tool/way through which we can calculates no of hopps?

over 2 years ago

0 shivakant dwivedi over 2 years ago

Prodigy 10 points

Hi Team,

0 shivakant dwivedi over 2 years ago

Prodigy 10 points

Hi Team,

0 shivakant dwivedi over 2 years ago in reply to shivakant dwivedi

Prodigy 10 points

Any update?

0 Ajeet Pal over 2 years ago

TI__Genius 12550 points

Hi Shivakant,

LMX2820 supports the instant calibration feature, which reduces the VCO calibration time and overall fast frequency hopping.

Datasheet shows the VCO cal timing 2.5usec and follow the section 8.1.3 for instant calibration procedure.

Regards,

Ajeet Pal

0 shivakant dwivedi over 2 years ago in reply to Ajeet Pal

Prodigy 10 points

Hi Ajeet,

Thanks for your reply.

Actually fast switching(hopping) depends other factor too like Analog loop filter settling time, programming time etc.

So i just want to know if including instant VCO calibration time of 2.5us , what will be the max & min locking time we can expect?

& one thing more: based on loop filter BW, how to calculate loop filter settling time in case of LMX2820?

0 Ajeet Pal over 2 years ago in reply to shivakant dwivedi

TI__Genius 12550 points

Hi Shivakant,

As you mentioned correctly, analog lock time depends on loop filter BW and as a thumb rule analog lock time can be 4times of loop filter BW time period based on settling tolerance frequency say 10kHz.

You can use the PLLatinum Sim tool to calculate the loop BW and see the lock time.

https://www.ti.com/tool/PLLATINUMSIM-SW

Regards,

Ajeet Pal

0 shivakant dwivedi over 2 years ago in reply to Ajeet Pal

Prodigy 10 points

Hi Ajeet,

Thanks for your reply.

Can you suggest what min phase margin i can consider for this loop filter design?
I have seen that for few filter BW, performance interns of jitter & lock in time is better at <45 degree phase margin should i go with this? or i have to consider > 60 degree phase margin?

just for example:

for BW=144KHz

@ 52 degree margin: jitter is 52 fs & lock in time is 14.4 us

where as @ 43 degree margin: jitter is 52.09 fs & analog lock in time 13.2 us

@ 65 degree margin : jitter is 50 fs & analog locking time 24.2 us

@ 40 degree merging: jitter is 53 fs & analog lock in time 13.9 us

@ 30 degree margin: jitter is 62 fs & analog lock in time is 24.1 us

settings configuration is shown below for this LMX2820.

0 Ajeet Pal over 2 years ago in reply to shivakant dwivedi

TI__Genius 12550 points

Hi Shivakant,

Usually you can go for higher loop bandwidth around 350kHz and phase margin 70deg for optimized phase noise performance.

LMX2820EVM using the same loop BW settings and you can validate the settling time with it.

Regards,
Ajeet Pal

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LMX2820: Related to frequency hopping