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LMX2594EVM: Phase noise performance of the LMX series PLLs

inbavanan S
Prodigy 20 points
Part Number: LMX2594EVM
Other Parts Discussed in Thread: LMX2594, LMX2820

Hi,

We are planning to use the PLL  LMX2594 or LMX2820 for our comb generation application. Below is the frequency which we will be generating using PLL using 120MHz Centum OCXO or 100MHz Wenzel OCXO

Spot 1: 4680MHz

Spot 2: 5040MHz

Spot 3: 5400MHz

Request you to share the tested results of the following.

1. Phase noise plots from 100Hz offset to 10MHz offset for 5400MHz output ( For LMX2594 and LMX2820)

2. Spectrum plots with 1000MHz Span  and RBW 5MHz for 5400MHz output, to check the SNR of the output

3. Frequency settling time while changing the frequency outputs of PLL from 4680 to 5400MHz vice versa

Regards,

INBAVANAN

  • 0
    TI__Guru** 107030 points

    Hi Inbavanan,

    Thank you for your interest in our products. Unfortunately, due to Covid-19, we have very limited lab access, we are not able to support general test data request. Alternatively, you can use PLL Sim to find out the phase noise of these devices at the frequencies you want. This tool also support frequency switching time simulation. 

  • 0 in reply to Noel Fung
    Prodigy 20 points

    Hi Noel,

    Thanks for your reply, we have purchased LMX2820 EVB and validated the phase noise requirement for our application.

    We got the confirmation on the Static condition phase noise requirement with LMX2820. 

    Additionally, can you confirm the phase noise performance in the Dynamic condition? If possible please share the Dynamic condition PLL phase noise plots.

    We are planning to use the IC LMX2820 PLL in our RF Board for X Band Output generation, Our OCXO will be a vibration qualified Wall mount part from Centum Electronics.

    Our end application will be Airborn, So we will be validating our DUT for vibration tests as per the below levels.

    Standards: MIL-STD-2164 and MIL-STD-810F

    Random Vibration:

    15 to1000 Hz:  0.02 g2/Hz (PSD)

    1000 to 2000 Hz:  – 6 dB / octave

    Duration: 1 Hr / Axis for all 3-axes

    Regards,

    INBAVANAN

  • 0 in reply to inbavanan S
    TI__Guru** 107030 points

    Hi Inbavanan,

    We don't have the facility to perform this kind of test in-house, I am afraid we are not able to provide test data in this condition.

  • 0 in reply to Noel Fung
    Prodigy 20 points

    Dear Noel,

    Note: We have purchased LMX2820EVB for phase noise testing only, the actual application we will be using the LMX2820 IC in our RF board.

    We are considering PLL phase noise of -106dBc/Hz @1KHz Offset as per the datasheet for my final output requirement. since this is a static condition will there be any degradation in the PLL phase noise during the dynamic conditions ( Under vibration) ? or I can consider the same phase noise performance for static and dynamic conditions also?

    If so, can we get the impact on the PLL phase noise performance under dynamic conditions based on the application note as given below for the TI oscillator?

    https://www.ti.com/lit/an/snaa296/snaa296.pdf?ts=1632808853431&ref_url=https%253A%252F%252Fwww.google.com%252F

    Our final motive is will there be any phase noise degradation during vibration conditions from the static condition result mentioned in the datasheet.

  • +1 in reply to inbavanan S
    TI__Guru** 107030 points

    Hi Inbavanan,

    Assuming the loop bandwidth is over 100kHz, at 1kHz offset, the phase noise is dominated by the reference clock + PLL noise (not VCO).

    PLL noise is usually not sensitive to vibration, just like other silicon devices. So the vibration performance at 1khz will depend mainly on the reference clock. Since you have a proven reference clock, then I think the overall vibration performance at this offset frequency should be good.

    Please note that, if you are looking for -106dBc/Hz at 1kHz offset at 5.4GHz, LMX2594 may not be able to meet this requirement. LMX2820 is a better choice but without many margin.