• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 19 subscribers
  • Views 246 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LMX2592: LMX2592 bypass capacitors

Bence Cseppento
Prodigy 20 points
Part Number: LMX2592
Other Parts Discussed in Thread: LMX2582

Dear Experts,

I am a student designing a synthesizer using the LMX2592 chip in a 1GHz band around 9GHz. I have a question about the 0.1, 1,10uF bypassing capacitors recommended by the datasheet. For what frequency are these values recommended, what frequency are they supposed to bypass (OSCin, PFD, VCO, RF)? It is essential as my 100nF capacitors are fine for coupling the OSCin signal but for the RFout I am using Johanson capacitors designed for microwave use.

Should I modify the recommended values according to my design? As there are bypasses for RF buffer, registers and the VCO I imagine I should, but the datasheet is unclear for me in this matter.

On a sidenote, but not that important (maybe it's a secret) could I get some insights regarding the VCOs? Will they produce a square wave or a sinusoidal signal

Thank you for any responses!

Regards,
Bence Cseppentő

  • 0
    TI__Mastermind 27581 points

    Bence, 

    for the 10 uF caps for the VCO output pins, you want something with low ESR and with low impedance in the 100k-5MHz range or so.

    For some of these 0.1 uF capacitors, I haven't seen them impact spurs or phase noise much, but as we can't know every possible setup condition, they are there just to be sure.

    The LMX2582 has a lot if internal regulators, so external bypassing does not have that much of an impact, except for the pull-up resistors on the output pins;  for these, bypassing is critical.

    Fancy microwave capacitors will work, but they likely might be overkill.

    Regards,
    Dean