WEBENCH® Tools/CDCE62002: Loop filter for cdce62002

lin huang

Part Number: CDCE62002
Other Parts Discussed in Thread: CDCE62005

Tool/software: WEBENCH® Design Tools

Dear Team：

The part is CDCE62002,the input frequency is 37.125MHz(LVCMOS),the output frequency is 74.25MHz(LVDS)；

Designing the loop filter，Using the same RC filled into Loop filter Tool and WEBENCH Designer，but the different phase margin、loop bandwidth output，which is the best？

thanks

over 5 years ago

0 Lane Boyd over 5 years ago

TI__Genius 16845 points

It is better to configure the loop filter for your application by following the procedure from this e2e post. I have pasted the procedure below for reference: https://e2e.ti.com/support/clock-and-timing/f/48/p/769060/2844477#2844477

Here is a procedure for designing a loop filter using the CDCE62005 EVM GUI:

Press the button "Loop Filter" in CDCE62005 EVM GUI
Input "Phase Margin" between 45~75 degrees
Select " loop bandwidth" ( normally < Phase Detect Frequency / 15 ). If the input reference clock is noisy, a narrow loop bandwidth could achieve better jitter performance.
Check "Standard Value"
Press the button "Suggest RC's". You may get new RC's value. If there is no exact R or C in hand, select a close value. Then press the button "Calculate Output (Using RC Input)" to update Phase Margin (PM) and Loop Bandwidth (LBW). Make sure that PM and LBW are still in the range of step 1 and 2.

I hope this information helps.

Kind regards,
Lane

0 lin huang over 5 years ago in reply to Lane Boyd

Prodigy 210 points

Hi：

My confusion is ：the same R2、C1、C2 input，but the different output（phase margin、loop bandwidth）between "Loop Filter" in CDCE62002 EVM GUI and WEBENCH Designer，which one is more accurate？pictures above show the detail parameters

thanks

0 Lane Boyd over 5 years ago in reply to lin huang

TI__Genius 16845 points

Thank you for the clarification, I misunderstood your original question.

The WEBENCH result should match the GUI calculation once you input the VCO Gain.

Kind regards,
Lane

0 lin huang over 5 years ago in reply to Lane Boyd

Prodigy 210 points

the output are same once I input the VCO gain

thank you very much

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WEBENCH® Tools/CDCE62002: Loop filter for cdce62002