LMX2594: tuning speed

Aaron Spaete

Part Number: LMX2594

Team,

My customer has the following question.

The issue I’m having is a long tune time at the VCO band breaks around 12 GHz (around 600 us) and 13.9 GHz (around 300 us). This occurs for tunes from one VCO to another. I am using the recommended settings as follows below from the datasheet.

Between 11.9 and 12.1 GHz

VCO_SEL = 4

VCO_DACISET_STRT = 300

VCO_CAPCTRL_STRT = 1

Everywhere else

VCO_SEL = 7

VCO_DACISET_STRT = 300

VCO_CAPCTRL_STRT = 183

If I set the QUICK_RECAL_EN bit high, then the tune time drops to around 300 us for 12 GHz and around 50 us for 13.9 GHz. I read in the datasheet that QUICK_RECAL_EN shouldn’t be done between 11.9 and 12.1 GHz. Can you provide more information about that? That bit is the only way I have found to speed things up. Maybe you have some other suggestions for me to try to speed up those spots.

Regards,

Aaron

over 5 years ago

0 Noel Fung over 5 years ago

TI__Guru** 106770 points

Hi Aaron,

Could you provide an example?

For example, from xxGHz to yyGHz.

Also, what are the configuration like OSCin freq, fpd freq, etc.

0 Noel Fung over 5 years ago in reply to Noel Fung

TI__Guru** 106770 points

Hi Aaron,

Any feedback from the customer?

0 Aaron Spaete over 5 years ago in reply to Noel Fung

TI__Expert 4527 points

Noel,

I just saw this response come through from another channel:

Between vco4 and 5, there is a region you must force it to choose 5 but the cal chooses 4. If you don’t do this, you could potentially fail lock over temperature

So if you set 4 as in the data sheet, the VCO first tries 4 , but this is in a gap, so it reverts to 5 that has much more tuning range to account for frequency drift

To speed up lock time, you can

1. Choose your method, but in extreme cases, might not hold lock over temperature without recalibration

2. For a single part, read back the settings in this range and force this with full assist. However, this has to be done individually for each part

Regards,

Aaron

0 Noel Fung over 5 years ago in reply to Aaron Spaete

TI__Guru** 106770 points

Hi Aaron,

That's right. So, did it help?

Clock & timing

Clock & timing forum

LMX2594: tuning speed