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LMX1204: does not work at 30MHz?

Kazuhiko Hirano
Genius 15038 points
Part Number: LMX1204
Other Parts Discussed in Thread: LMK1D1204

Tool/software:

Hello,

My customer is looking for a clock buffer/distribution to meet the following design requirements.
Input: single-end 50MHz sinewave, amplitude = 0dBm to +4dBm at 50ohm termination to GND.

Output: Differential LVPECL or LVDS
Output additive jitter: <100fs

They are considering LMX1204 as a candidate. But the datasheet says operating frequency range is 300MHz to 12.8GHz. The LMX1204 really does not work at 30MHz?
Or, any other TI clock buffer meeting their requirements?

Best regards,

K.Hirano

  • 0
    TI__Expert 8820 points

    Hi Kazuhiko-san,

    The LMX1204 cannot work as an input frequency below 300 MHz. See the following E2E for more details: https://e2e.ti.com/support/clock-timing-group/clock-and-timing/f/clock-timing-forum/1456564/lmx1204-min-input-frequency

    I am a bit confused by your input signal. Are you inputting a sine wave whose amplitude varies from 0 dBm to 4 dBm (meaning, the peak-to-peak voltage varies by up to 370 mV), or are you inputting a sine wave with a swing of 185 mV, with the peaks at 501 mV and the troughs at 316 mV? If the latter is the case, you will have a slew rate of approximately 0.03 V/ns, and the LMK1D1204 accepts a minimum input swing of 0.05 V/ns. This DS specification is measured from 20-80% of the input swing, so you should be okay with your sine wave as an input. Just be sure to bias the other pin of the differential input to the common mode voltage of your sine wave. 

    Thanks,

    Michael