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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,

Thanks your for your suggestion. I try your method that inject 73.351MHz(not 73.35MHz) as IF input signal, and capture the data. The result of -37dBm looks good, but the ssi raw data is very small when input level is -90dBm

This is -37dBm IQ data

This is -90dBm IQ data, you can see the amplitude is very small.

Raw data is attached. In the txt file, the line with length 0064 is IQ data, the line with lenght 0032 is the last 16 bit of SSI data, which is ATTN+RSSI.

I have another question about the ATTN and RSSI value in the last 16 bit SSI data, I am a little confused for these values.

1). Set register 06 to 00 which disables AGC, when input IF is -70dBm, the IQ data is very very samll almost 0, and the last 16 bit data is about 0x2900(ATTN = 0x29,RSSI=0)

2). Set register 06 to 81 which enables AGC, when input IF is -70dBm, the IQ data is bigger, and the last 16 bit data is 0x0000.

So my question is:

- What exactly ATTN and RSSI mean? What the relationship of them to AGC? The ATTN is introduced by AGC or by other component? In my mind, when the signal is small, the AGC should amplifies the small signal, right?

fenghuo_cw@163.com

attachments.zip
• Hi PMH,

Thanks your for your suggestion. I try your method that inject 73.351MHz(not 73.35MHz) as IF input signal, and capture the data. The result of -37dBm looks good, but the ssi raw data is very small when input level is -90dBm

This is -37dBm IQ data

This is -90dBm IQ data, you can see the amplitude is very small.

Raw data is attached. In the txt file, the line with length 0064 is IQ data, the line with lenght 0032 is the last 16 bit of SSI data, which is ATTN+RSSI.

I have another question about the ATTN and RSSI value in the last 16 bit SSI data, I am a little confused for these values.

1). Set register 06 to 00 which disables AGC, when input IF is -70dBm, the IQ data is very very samll almost 0, and the last 16 bit data is about 0x2900(ATTN = 0x29,RSSI=0)

2). Set register 06 to 81 which enables AGC, when input IF is -70dBm, the IQ data is bigger, and the last 16 bit data is 0x0000.

So my question is:

- What exactly ATTN and RSSI mean? What the relationship of them to AGC? The ATTN is introduced by AGC or by other component? In my mind, when the signal is small, the AGC should amplifies the small signal, right?

fenghuo_cw@163.com

attachments.zip
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