FPGA Questions


#1

Hi all,

I have dived into the fpga code and I have now much clearer picture of
what is going on, but also much more questions :slight_smile:

The Tx CORDIC is disabled in the code I checked out. Why?

I have failed to find a description of how to control the AD9862 chip on
the Analog Device web site. Where is this documented?

I would like to be able to choose the power level and the channel used
to transmit every packets. To choose the channel, is it possible to
tweak the CIC Decimating filter to slightly alter the signal frequency
or is it a better idea to do it in the AD9862?
How can I choose the power level? To me, it looks like this job has to
be done on the daughter board.

Best regards,
Thibaud


#2

On 2/24/07, Thibaud H. removed_email_address@domain.invalid wrote:

Hi all,

I have dived into the fpga code and I have now much clearer picture of
what is going on, but also much more questions :slight_smile:

The Tx CORDIC is disabled in the code I checked out. Why?

I could be wrong, but I think the TX CORDIC is disabled due to the
fact that the samples being delivered over USB are already complex.
Any other frequency translation is done within the AD9862 transmit
path.

Anyone can feel free to correct me if I am wrong.

I have failed to find a description of how to control the AD9862 chip on
the Analog Device web site. Where is this documented?

http://www.analog.com/UploadedFiles/Data_Sheets/AD9860_9862.pdf

I would like to be able to choose the power level and the channel used
to transmit every packets. To choose the channel, is it possible to
tweak the CIC Decimating filter to slightly alter the signal frequency
or is it a better idea to do it in the AD9862?
How can I choose the power level? To me, it looks like this job has to
be done on the daughter board.

By channel, do you mean I/Q or do you mean specific frequencies? You
should always drive the baseband signal going out to the AD9862 to
full scale to minimize quantization noise - but transmit power should
be controlled via an auxiliary DAC that is on the AD9862 and being
sent to the daughterboard. Does that make sense?

On a side note, the CIC filters on the TX side are interpolating - not
decimating.

Best regards,
Thibaud

Good luck,
Brian


#3

On Sat, Feb 24, 2007 at 05:13:22PM -0500, Brian P. wrote:

Any other frequency translation is done within the AD9862 transmit
path.

Anyone can feel free to correct me if I am wrong.

You are correct :wink:

I have failed to find a description of how to control the AD9862 chip on
the Analog Device web site. Where is this documented?

http://www.analog.com/UploadedFiles/Data_Sheets/AD9860_9862.pdf

I would like to be able to choose the power level and the channel used
to transmit every packets. To choose the channel, is it possible to
tweak the CIC Decimating filter to slightly alter the signal frequency
or is it a better idea to do it in the AD9862?

The CIC interpolator doesn’t perform freq translation.

If you want to change the channel, you’ll want to issue the equivalent
of a “tune” command (probably several sub-operations inband)
immediately prior to sending the samples for the packet.

Yes, I know you’re waiting for me to flush out the packet format.

Eric


#4

Eric B. wrote:

Actually, he isn’t. The TX CORDIC is not used since the AD9862 has its
own upconverter. It doesn’t have anything to do with whether the
samples are real or complex.

Matt