LMX2571: 4 FSK modulation of LMX2571

Kailyn Chen

Part Number: LMX2571

Hello,

Our customer use LMX2571 with 4FSK modulation, and all the registers wrote right, but the output deviation is not correct, for example, the carrier frequency is 180Mhz, and setting the frequency deviation is +-10Khz and +-20khz, but the output frequency is 180Mhz. While carrier frequency is 20KHz, the output frequency deviation is +-2KHz. So could you please help to analysis?

Best regards
Kailyn

over 6 years ago

0 Noel Fung over 6 years ago

TI__Guru** 108440 points

Hi Kailyn,

Make sure they have calculated the frequency deviation correctly using the equations as shown in Table 32 in the datasheet.

Make sure also that DEN is set to zero or 2^24 - 1.

See datasheet section 8.2.1 for an example.

0 Kailyn Chen over 6 years ago in reply to Noel Fung

TI__Genius 9560 points

Hi Neol，

Thank you for your reply and the customer did set the DEN zero, but the frequency deviation is not correctly. So is there any limitation of the frequency deviation? For example, the deviation is not exceed 10KHz of 180MHz, or the deviation is not exceed 4KHz of 48Mhz.etc?

Best regards

Kailyn

0 Noel Fung over 6 years ago in reply to Kailyn Chen

TI__Guru** 108440 points

Hi Kailyn,

What is the fpd frequency?

Clock & timing

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LMX2571: 4 FSK modulation of LMX2571