LMX2694EPEVM: Loop Filter Calculation

user4619635

Prodigy 160 points

Part Number: LMX2694EPEVM

Hi,

LMX2694-evaluation module has following loop filter configuration:

However, I could not reach these values by using PLLatinum Sim. The configuration is below:

Could you please explain your method to obtain loop filter configuration given in Table1?

Regards,

over 3 years ago

0 Noel Fung over 3 years ago

TI__Guru* 81580 points

Hi There,

Your pictures did not get through.

Anyway, to get the EVM loop filter values, in addition to loop bandwidth, there are additional PLL parameters that we can set to make the tool return the EVM values.

0 user4619635 over 3 years ago in reply to Noel Fung

Prodigy 160 points

Hi,

Thank you for your quick reply.

C1 value is given as 470pF in 2694EVM Evaluation Instructions (in Table 1). However, C1 is calculated as 390pF in your calculation.

Using 470pF in the loop provides an advantage or not?

Regards,

0 Noel Fung over 3 years ago in reply to user4619635

TI__Guru* 81580 points

Hi There,

In the PLL block diagram, you can type in the C1 value, 0.47 in this case, PLL Sim will calculate the Actual loop characteristic to you. The difference between 470pF and 390pF is actually very small.

0 user4619635 over 3 years ago in reply to Noel Fung

Prodigy 160 points

Hi,

I checked your proposed simulation window once again and realize that:

If you click "calculate loop filter" button in your software, actual values will be changed. Could you please re evaluate?

Regards,

0 Noel Fung over 3 years ago in reply to user4619635

TI__Guru* 81580 points

Hi There,

There are two ways to do the simulation.

If you click "calculate loop filter", the tool will calculate the loop filter values to you based on your input to "Design Target".

Or you can input your loop filter values and then the tool will calculate the "Actual" loop performance to you.

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LMX2694EPEVM: Loop Filter Calculation