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# Why AD9864 output is noise when input IF signal is -90dBm

Our product is using AD9864, by out test, when the input IF signal with level of -90dBm directly into AD9864, and the DSP capture AD9864 SSI output IQ data then draw it with Matlab, the data is almost noise, we can't see valid signal. For -70dBm input or -30dBm input, the IQ data looks ok.

So, what's the possible reason for my problem, hardware or AD9864 configuration issue? Could anyone help me? Also I want to know what's the smallest input level that AD9864 can accept.

Here is my AD9864 register setting. And my IF input freq is 73.35MHz, LO freq is 71.1MHz.

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• Hi PMH,

I attach the I and Q data for you.

Also i measured the SSI last 16 bits(ATTN+RSSI) for different reg setting and different input IF signal level. The result is as below table. But I still have some question as below. One note that my signal generater may have some RF loss that input -30dBm the actual value is -34dBm, so I set reg06 to 82 not 81.

1) Only for the condition of reg06 = 82/81, the RSSI field is to start changing "0" value around -65 dBm signal level (with ATTEN=0x00). For other case, the RSSI filed starts changing 0 after input level is bigger than -60dBm.

2) How to calculate the estimated RSSI with the SSI last 16 bits? For example, in table line 15, the estimated RSSI = -(65dBm - 11dBm) = -54dBm? What about line 16 with ATTN is not zero?

3) What does ATTN exactly mean here? For example from table line 15 to 16, the ATTN is changing from 00 to 26, what can I do with this value?

4) Compare to line 45 and line 50, the difference is ATTN is changed from 0 to 1, could you explain why it changes like this?

Sorry that I have so many questions to bother you.

attachments.zip
• Hi PMH,

I attach the I and Q data for you.

Also i measured the SSI last 16 bits(ATTN+RSSI) for different reg setting and different input IF signal level. The result is as below table. But I still have some question as below. One note that my signal generater may have some RF loss that input -30dBm the actual value is -34dBm, so I set reg06 to 82 not 81.

1) Only for the condition of reg06 = 82/81, the RSSI field is to start changing "0" value around -65 dBm signal level (with ATTEN=0x00). For other case, the RSSI filed starts changing 0 after input level is bigger than -60dBm.

2) How to calculate the estimated RSSI with the SSI last 16 bits? For example, in table line 15, the estimated RSSI = -(65dBm - 11dBm) = -54dBm? What about line 16 with ATTN is not zero?

3) What does ATTN exactly mean here? For example from table line 15 to 16, the ATTN is changing from 00 to 26, what can I do with this value?

4) Compare to line 45 and line 50, the difference is ATTN is changed from 0 to 1, could you explain why it changes like this?

Sorry that I have so many questions to bother you.

attachments.zip
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