LMX2595: Set of Frequencies Programming and Lock Time Measurement with synthesizer

Anand P

Prodigy 150 points

Part Number: LMX2595
Other Parts Discussed in Thread: LMX2594, LMX2820

Tool/software:

Hello,

I am currently working with the LMX2595 synthesizer and had a couple of technical queries regarding its operation:

Frequency Programming with Trigger Control:
Is it possible to program the LMX2595 with a predefined set of frequencies, such that on receiving a trigger signal (either through a GPIO or SPI command), the synthesizer switches to the next frequency in the set? if not with the trigger, how to do this? If this functionality is supported, could you please guide me on how to implement it—specifically, the required configuration settings or register controls involved?
Lock Time Measurement:
Is there a method to measure the time taken by the synthesizer to lock onto a particular frequency after a frequency change command is issued? If so, I would appreciate your suggestion on how to accurately calculate or monitor this lock time—either through internal status flags, GPIO monitoring, or any available diagnostic outputs.

Your guidance on the above points will be greatly helpful for optimising the frequency hopping and measurement sequence in our application.

Looking forward to your response.

4 months ago

0 Noel Fung 4 months ago

TI__Guru** 109950 points

Hi Anand,

how many frequency sets do you need.

To measure lock time, set MUXOUT_LD_SEL to 0x1, measure the MUXout pin with a scope. MUXout will go LOW during programming and return to HIGH when it is locked to the new frequency.

0 Anand P 4 months ago in reply to Noel Fung

Prodigy 150 points

Hello Noel,

Thank you for this suggestion.

what is the maximum no.of frequencies it can able to program? we need around 200 frequencies.

0 Noel Fung 4 months ago in reply to Anand P

TI__Guru** 109950 points

HI Anand,

We don't have any synthesizer able to support 200 frequencies change with a trigger signal.

You need to program each frequency one by one.

0 Anand P 4 months ago in reply to Noel Fung

Prodigy 150 points

Hello Noel,

What is the maximum no.of frequencies it can support?

0 Anand P 4 months ago in reply to Anand P

Prodigy 150 points

can you please tell me, how to do that with number of frequency set?

0 Noel Fung 4 months ago in reply to Anand P

TI__Guru** 109950 points

Hi Anand,

LMX2594 can support two frequency set with the ramp function, definitely not enough to support your application.

Likely you need to operation LMX2594 in full-assist mode. This way you can change the frequency without doing any calibration, PLL lock time is shorter.

you can also consider LMX2820 in InstCal mode. The lock time can be further reduced to less than 20µs.

Please read below collaterals for details.

https://www.ti.com/lit/pdf/snaa336

https://www.ti.com/lit/pdf/snaa342

0 Anand P 4 months ago in reply to Noel Fung

Prodigy 150 points

Hello Noel,

Thank you for your suggestion regarding the use of full-assist mode for programming the LMX2595 synthesizer. We will proceed with this approach.

Our requirement is to configure the synthesizer to operate at a fixed set of frequencies ranging from 12.3 GHz to 14.3 GHz. To achieve this, I would appreciate your guidance on the following:

what are all the registers need to be modified to support this requirement?
Is there a specific order in which these registers must be programmed for proper functionality?

Your assistance in outlining the necessary register settings and the recommended programming sequence will be highly valuable.

0 Noel Fung 4 months ago in reply to Anand P

TI__Guru** 109950 points

Hi Anand,

The appnote, SNAA336, has outlined the programming procedure.

12.3G to 14.3GHz are within the VCO frequency, you don't need the VCO doubler, so you only need to change PLL_N, PLL_NUM, VCO_SEL, DACISET and CAPCTRL. For example:

0 Anand P 4 months ago in reply to Noel Fung

Prodigy 150 points

Hello Noel,

Thanks for the reply. can I apply these changes to the default configuration in TICS pro software? or else do I need to do some other changes also there?

0 Noel Fung 4 months ago in reply to Anand P

TI__Guru** 109950 points

Hi Anand,

You can setup TICS Pro to program and calibrate the device for the frequency you need, then do a register read back to get VCO parameters. Repeat this process to build the LUT for all the frequencies you need.

0 Anand P 4 months ago in reply to Noel Fung

Prodigy 150 points

Hello Noel,

I'm following this steps to setup synthesizer in full assist mode. and I read-back R110,R111,R112 registers for all my required frequencies. rb_VCO_CAPCTRL , rb_VCO_DACISET values are varying if I program it again. will it be like that? In such case what value can I consider?

0 Noel Fung 4 months ago in reply to Anand P

TI__Guru** 109950 points

Hi Anand,

each frequency has it own CAPCTRL, DACISET and VCO_SEL, you should apply the corresponding values for each frequency.

Clock & timing

Clock & timing forum

LMX2595: Set of Frequencies Programming and Lock Time Measurement with synthesizer