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LMK04208: Input sinwave 10MHz -> Output 30MHz LVCMOS

Hirotaka Matsumoto
Guru 27525 points
Part Number: LMK04208
Other Parts Discussed in Thread: LMK04808

Hi all

Would you mind if we ask LMK04208?

<Question1>
Our customer uses LMK04208 with following condtions;
-Input  :  sinwave 10MHz 0.5Vrms
-Output : 30MHz LVCMOS 3.3V
Is it possible?

<Question2>
If <Question1> is possible, should we select on TICSPRO at input?
Biploar??


<Question3>
We would like to simulate of phase noise.
PLLatinum doesn't correspond for this device.
How should we simulate?

Kind regards,

Hirotaka Matsumoto

  • 0
    TI__Mastermind 18070 points

    Hi Hirotaka,

    We will get back to you the next business day.

    Regards,
    Hao

  • 0
    TI__Mastermind 28990 points

    Hello Matsumoto-san,

    Q1: The limiting factor with sinewave input at low frequency is typically slew rate. The slew rate of a sine wave is given by:

    Slew (V/s) = 2π * Vpk (V) * Freq (Hz)

    = 2π * (sqrt(2) * 0.5Vrms) * (10e6 Hz) = 44.4e6 V/s = 0.044V/ns

    The datasheet for LMK04208 lists the minimum slew rate for CLKinX as 0.1V/ns, so the 10MHz sine wave does not meet the minimum slew rate requirements at that amplitude. The amplitude would need to be increased (0.1/0.44) * 0.5Vrms = 1.125Vrms, or about 3.2Vpp to meet the datasheet minimum specifications. This is higher than the maximum single-ended signal swing of 2.4Vpp. Therefore, single-ended 10MHz sinewave cannot not meet datasheet requirements.

    On the other hand, a 3.1Vpp sinewave into a balun, or a differential sinewave with half the amplitude (1.55Vpp) at each pin would be close enough to meeting datasheet minimum requirements at 10MHz (0.097V/ns), without exceeding the maximum differential signal swing limits. So if they use a 10MHz sinewave, they should couple it differentially to yield the highest signal amplitude.

    Q2: I recommend AC-coupling and using bipolar mode for sinewave input. 

    Q3: LMK04208 is the same die as LMK04808, so you can use LMK04808 to simulate LMK04208 performance.

    Regards,