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LMX2571: Sevreral questions

Hirotaka Matsumoto
Guru 27595 points

Part Number: LMX2571
Other Parts Discussed in Thread: LMX2572

Hi all

Would you mind if we ask LMX2571?

<Question1>
In case of digital FM, is it possible to use with "Arbitrary Audio signal from Microphone with 20 kHz bandwidth"?
The datasheet shows 1kHz, so our customer might use audio application.

<Question2>
We suspect that, in FSK mode, if the frequency shift is small, the VCO calibration may not be necessary.
If it is true, how much frequency offset can the device be operational without VCO calibration?
Is it the same as LMX2572?
https://e2e.ti.com/support/clock-and-timing/f/48/p/895901/3321375#3321375



Kind regards,

Hirotaka Matsumoto

 

  • 0
    TI__Mastermind 35100 points

    Hello Matsumoto-san,

    1. The LMX2571 supports FSK control through I2S at a rate of up to 100MHz. Every I2S frame contains 17 bits, so data could be streamed at up to ~5.88MSPS - more than enough for 20kHz audio bandwidth.
    2. LMX2571 has a narrow VCO range compared to LMX2572, and the VCO gain is smaller. I am not sure what the allowable range would be. I am looking into it, and will provide you an update when I have more information.

    Regards,

  • 0 in reply to Derek Payne
    TI__Guru** 120230 points

    Hi Matsumoto-san,

    the max. frequency deviation is defined in Equations 4 to 7 in the datasheet. For example, Equation 4 is used to calculate the code (FSK_DEVx_Fx) for a positive deviation in synthesizer mode. The code is 16-bit long. So you can use Equation 4 to determine the max. frequency deviation possible with your use case.