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High noise in IQ data near to full scale range

Question asked by fischer on May 30, 2017
Latest reply on Oct 23, 2017 by sripad

I have  following problem: I discovered high noise in my IQ data when the values are near to the full scale range of 12 bit (-2048 to 2047). The noise occurs at a value of ca. 1900 and become noticeable in jumping data samples. The jumping distance of the samples is up to a IQ value of 200 and more.

I don't understand, which part of the chip is producing this noise, are it the ADC or the filters? Though I get a ADC Small and Large Overload Signal for lower rx gain values, there is not yet this noise visible. Only for values near to a value of 1900 this noise occurs. Should I avoid to use the full scale range by managing the IQ data to stay below  a value of 1900?

 

I have following test setup:

- AD 9361

- TX Word I: 1450, TX Word Q: 1450, TX Attenuation: 3dB

- 768 MHz BBPLL, 12 MHz ADC, 3.2 GHz RFPLL

- Monitor as Input with a gain of 9,5dB Front Gain and 24 dB GBBF Gain

- Fro TX and RX: HB3 at 3, HB2 and HB1 at 2, FIR bypassed

- No Tracking

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