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# AD9361 IIO Oscilloscope noise floor

Hello,

In this configuration:

I see this spectrum:

This measure was made on the PicoZed SDR 2x2 SOM. There was no signal at the input.

Why is there more noise around -Fs/2 and +Fs/2?

Best regards,

Vincent

Parents
• More noise around fs/2 is due to sigma delta ADC noise shaping, When RF gain is very small, RF signal chain noise floor is dominated by the ADC Nosie floor, if the Over Sampling Ratio is big enough, (HB1/2/3 enable), It makes the K >=8, so the inband Nosie floor ( DC~fs/2 ) [fs=output DataRate] is flat. if K=1, the noise floor is the standard sigma-delta noise floor as observed.

• More noise around fs/2 is due to sigma delta ADC noise shaping, When RF gain is very small, RF signal chain noise floor is dominated by the ADC Nosie floor, if the Over Sampling Ratio is big enough, (HB1/2/3 enable), It makes the K >=8, so the inband Nosie floor ( DC~fs/2 ) [fs=output DataRate] is flat. if K=1, the noise floor is the standard sigma-delta noise floor as observed.

Children
• Hello,

You said " if the Over Sampling Ratio is big enough, (HB1/2/3 enable), It makes the K >=8, so the inband Noise floor ( DC~fs/2 ) [fs=output DataRate] is flat.". But in my configuration, HB1/2/3 are enabled as F_adc = 8 x F_rxsamp.

So, is it normal that the noise floor is not flat?

Best regards,

Vincent

• You said " if the Over Sampling Ratio is big enough, (HB1/2/3 enable), It makes the K >=8, so the inband Noise floor ( DC~fs/2 ) [fs=output DataRate] is flat.". But in my configuration, HB1/2/3 are enabled as F_adc = 8 x F_rxsamp.

So, is it normal that the noise floor is not flat?

• So, what are the conditions to have a flat noise floor?

Best regards.

• I see that your are not using FIR, is there any reason? if not enable FIR and try.

You can use the Filter wizard to generate required config and filter.

What is your sampling rate and BW requirement?

You can optimize your decimation such that ADC is at highest rate for your required data rate. In other way try to keep the OSR high enough.