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Original question:

LMX2594: single ended RF clock power Range

LMX2594: Clock reference termination for single ended clipped sine wave sources

Keith clark
Prodigy 130 points
Part Number: LMX2594

Hi,

We wish to use one of your LMX2594 frequency synthesizers in a project. I wonder if you can help with a technical query?

Unfortunately our prototype in circuit LMX2594 synthesiser did not have the phase performance we were hoping for. Some of this was due to power supply layout and the revised circuit makes use of better ground planes and low drop out regulators to help ensure clean supplies. Ideally we would use a 100 MHz LVDS 1ppm TCXO with good phase noise as a frequency reference. We tried several types both, single ended and differential, but still did not get good phase noise performance at an output of 8.2 GHz. He are now hoping to use a clipped sine wave Rakon device.

 The load requirements for this are :

Load resistance = 10 kOhms

Load capacitance = 10 pF

Can these requirements be met with the need for a 0.1uF AC coupling capacitor?

If so what configuration would you recommend please?

Many thanks for any help you can offer.

Best regards

Keith

  • 0
    TI__Guru** 108130 points

    Hi Keith,

    At 100MHz, the slew rate between sine wave, clipped sine wave and square wave is not big, the slew rate should not be a hurdle to the phase noise. The phase noise of the reference clock becomes important in this case, especially if you are interested in the close-in phase noise.

    With a TCXO, you can directly AC-couple it to the OSCINP pin, the OSCINM pin can be AC-coupled to ground.