AnsweredAssumed Answered

AD9361 Tx frequency offset of different LO Control

Question asked by RobertYJ on Jun 27, 2017
Latest reply on Jun 27, 2017 by RobertYJ

MY RF is AD9361 FMCOMMS3.

 

I use this function to send the DDS signal,

dac_init(ad9361_phy, DATA_SEL_DDS, 0);

 

and my DDS signal is setting to 0.1MHz=100KHz

dds_default_setup(phy, DDS_CHAN_TX1_I_F1, 90000, 100000, 250000);
dds_default_setup(phy, DDS_CHAN_TX1_I_F2, 90000, 100000, 250000);
dds_default_setup(phy, DDS_CHAN_TX1_Q_F1, 0, 100000, 250000);
dds_default_setup(phy, DDS_CHAN_TX1_Q_F2, 0, 100000, 250000);

 

Below is the clock path

/* Rate & BW Control */
{983040000, 245760000, 122880000, 61440000, 30720000, 30720000},//uint32_t rx_path_clock_frequencies[6] *** adi,rx-path-clock-frequencies
{983040000, 122880000, 122880000, 61440000, 30720000, 30720000},//uint32_t tx_path_clock_frequencies[6] *** adi,tx-path-clock-frequencies

 

I found that if I use different LO Control I will get the different frequency offset on the spectrum

 

  /* LO Control */
2412000000UL, //rx_synthesizer_frequency_hz *** adi,rx-synthesizer-frequency-hz
100000000UL, //tx_synthesizer_frequency_hz *** adi,tx-synthesizer-frequency-hz

 

  /* LO Control */
2412000000UL, //rx_synthesizer_frequency_hz *** adi,rx-synthesizer-frequency-hz
600000000UL, //tx_synthesizer_frequency_hz *** adi,tx-synthesizer-frequency-hz

when I set the tx_synthesizer_frequency_hz to 600MHz it will offset 3750Hz

 

/* LO Control */
2412000000UL, //rx_synthesizer_frequency_hz *** adi,rx-synthesizer-frequency-hz
900000000UL, //tx_synthesizer_frequency_hz *** adi,tx-synthesizer-frequency-hz

when I set the tx_synthesizer_frequency_hz to 900MHz it will offset 6250Hz

 

/* LO Control */
2412000000UL, //rx_synthesizer_frequency_hz *** adi,rx-synthesizer-frequency-hz
1800000000UL, //tx_synthesizer_frequency_hz *** adi,tx-synthesizer-frequency-hz

when I set the tx_synthesizer_frequency_hz to 1800MHz it will offset 12500Hz

 

/* LO Control */
2412000000UL, //rx_synthesizer_frequency_hz *** adi,rx-synthesizer-frequency-hz
2400000000UL, //tx_synthesizer_frequency_hz *** adi,tx-synthesizer-frequency-hz

when I set the tx_synthesizer_frequency_hz to 2400MHz it will offset 17500Hz

 

If the LO Control is larger then the frequency offset is larger too.

What problem cause this situation?

 

Please help me to solve this problem!!

 

Thank you!! 

 

 

---------------------------------------------New Edition---------------------------------------------

I found a document about "Tuning the AD9361/AD9364"

Tuning the AD9361/AD9364 [Analog Devices Wiki] 

The part of Impact indicate some deviate may happen with <18.1ppm

So I calculate the frequency offset of above is about 7ppm(3750/600M,6250/900M,12500/1800M,17500/2400M).

Is this issue occur the frequency offset??

 

Thanks for your help!!

Outcomes