Monday, 29 November 2010

Still experimenting

I have not updated the blog for a few days so here is what is going on.
Currently I am working on a simple SDR using the Terasic DE1 board
and the ADC/DAC board I bought.

Please bear in mind I am a novice FPGA programmer so this is taking
some time to do / learn. I have a working implementation of the Cordic
algorithm running on the board. It produces a sine and cosine output for
a given input angle. By accumulating the angle you can generate an oscillator
with two outputs that have a 90deg phase difference between them.
Looking on a spectrum Analyser the output is as clean as would be expected
for a 14 bit implementation.

The oscillator is used with a half complex mixer to translate the wanted
frequency down to baseband. The I and Q channels are then filtered and
decimated. I have the CIC filters written but not tested. A CIC filter is a type
of filter that is implemented solely with additions and subtractions.

Currently I am working on the I2C code to control the audio output codec
which will enable me to hear whether I am receiving anything!

The test card project is on hold at the moment. I am waiting for delivery of
a simple FPGA board from China. I have soldered the 3 channel DAC I received
from Analog Devices onto a small PCB. When I get the FPGA board from
the Middle Kingdom I will post some pictures and maybe a short Video when I
get the code working.

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