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AD9542 loop filter structure and components' values

Category: Hardware
Product Number: AD9542

I'm a DFAE in Japan.

My customer asked me what is the frequency response of the loop filter and how to choose components' values(R1, C2, R3) in registers (0x1082).

Is 3.9nF capacitor between LFx pin and LDOx pin a part of the loop filter and does it affect loop filter frequency response?

Parents
  • Hi,

    the data sheet states that the external capacitors are necessary for proper operation of the loop filter, but more information I do not have. The phrase about contacting ADI for assistance is not anymore actual. That knowledge is lost. 

    The AD9545 data sheet (which we recommend to use because the AD9542 data sheet is still at rev 0 and AD9545 data sheet is at rev C) also says that for best performance, use the components default values.

    My recommendation is that if they want to influence the phase noise response of the AD9542, they should use the charge pump current. See the attached presentation. But understand that what you gain on the left side of the loop bandwidth (260kHz), you loose on the right side. And vice versa.

    PDF 

    Petre

Reply
  • Hi,

    the data sheet states that the external capacitors are necessary for proper operation of the loop filter, but more information I do not have. The phrase about contacting ADI for assistance is not anymore actual. That knowledge is lost. 

    The AD9545 data sheet (which we recommend to use because the AD9542 data sheet is still at rev 0 and AD9545 data sheet is at rev C) also says that for best performance, use the components default values.

    My recommendation is that if they want to influence the phase noise response of the AD9542, they should use the charge pump current. See the attached presentation. But understand that what you gain on the left side of the loop bandwidth (260kHz), you loose on the right side. And vice versa.

    PDF 

    Petre

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