AD9681 balun stage

Hi Hoang,

Thanks for your interest in AD9681. Even though that balun's datasheet rating is 4.5MHz, it works well at lower frequency. How low of a frequency do you need?

Thanks,

Doug

I test with 500kHz square of arbitrary signal generator. I met the low frequency loss and phase shift. 

How is about 500kHz or 1MHz?

Hi,

I thought 500kHz would be OK, but if you have tried it and it does not meet your need, the AD9681 evaluation board also has pads that can accommodate a Mini-Circuits ADT1-1WT+, which is rated down to 400kHz.

You would need to remove the two MABA-007159-000000 and install the  Mini-Circuits ADT1-1WT+.

The AD9681 evaluation board schematic is here: wiki.analog.com/.../08_039100b_cam.zip

Thanks,

Doug

Thank you Dougl. Is there any examination you test with it? 

Hi,

We use single tone sinusoid as an initial test signal for many of our tests. I don't have specific test conditions for the Mini-Circuits balun but you could try a 500kHz single tone test as a starting point.

At some point the impedance of the 0.1uF AC coupling capacitors could be an issue for you to be aware of.

Doug

Hi Dougl, 

I replace the balun stage to Mini - circuits but the result I got was the same with the older one at 500kHz.

Here is my result. square waveform at 500kHz.

I try to see the voltage spectrum. 

Could you tell me the problem and recommend what should I do?

Thank you.

HOANG

Hi Dougl, 

I replace the balun stage to Mini - circuits but the result I got was the same with the older one at 500kHz.

Here is my result. square waveform at 500kHz.

I try to see the voltage spectrum. 

Could you tell me the problem and recommend what should I do?

Thank you.

HOANG

Hi Hoang,

How does the waveform look if you apply a 500kHz sinusoid?

Thanks,

Doug

Hi Dougl,

Sinunoid looks well. 

Another question. Why was my signal voltage probe at SMA connector pin decreased by 2? example: 2Vp-p Sinunoid signal generator --> at SMA connector pin: 1.2Vp-p 

Thanks,

HOANG

Hi Dougl,

In hadv6 document, Author said about the registers from 0x0100 to 0x011F. But I can't see its information. Could I reprogram the hdl code and write those register via spicontroller software?

Thanks 

HOANG

Hi Hoang,

In SPIController, you can read and write FPGA registers.

In the SPIController GUI, use the menu to navigate Config --> Controller Dialog. Then in the Controller Dialog, under "FIFO Chip Sel #" you can select FPGA. Then the register reads and writes in the GENERIC READ/WRITE window will be to the FPGA.

You normally do not need to change FPGA registers to capture data from AD9681. Reprogramming the FPGA and changing register values could cause unpredictable behavior. Proceed with caution and at your own risk.

Thanks,

Doug

Thanks a lot Doug.

Could you answer something about my previous question related to voltage in ADC board?

HOANG 

Hi Doug,

In my project, I need to write many data into FPGA via SPI register. Is there any way I could directly write it (example: by C/C++). 

Because I don't want to write each address in here.

Thanks,

HOANG 

Hi Hoang,

Regarding the voltage, do you see the reduced voltage with a load, or is it with no load? Are you measuring the voltage at the signal generator, or is it based on what the signal generator settings are?

I have not tried it in a long time but there is a macro capability in SPIController. Do you think this will help you? Here is the path to some SPIController documentation: AN-878 High Speed ADC SPI Control Software Application Note (Rev. A) (analog.com)

Doug