Oussama Sekkat wrote:
Hi,
Thanks for your reply.
So from what I understand, in the transmit side the digital up
converters are implemented in the AD9862 chip but the interpolation is
done in the FPGA.
On the transmit side we use our own CIC to interpolate from whatever
ratio comes over the USB to 32 MS/s. This is sent to the 9862 which
then interpolates again by a factor of four to bring us to 128 MS/s.
The upconverter is in the 9862 as you say.
I believe in the receive side the down conversion is done in the FPGA.
Yes, because the 9862 does not have a downconverter in the RX path.
So why can't we do the same for the transmit side and implement the
Digital Up Converters in the FPGA?
Not sure what you would gain from this -- You would use a lot more area
in the FPGA.
Anyway, the bus going to the TX path on the 9862 is multiplexed (I then
Q samples), and we run it at our normal clock rate of 64 MHz. This
means we can only get 32 MS/s complex across it. If we did the
upconversion in the FPGA, we would thus be limited to about a 12 MHz
carrier.
Also, the AD9862 chip contains interpolation filters as well. Could
those be used instead of the CIC interpolators on the FPGA? that way
both the up conversion and the interpolation would be done in the
AD9862 chip and more space would be available on the FPGA.
We use those interpolation filters already, but they only do a factor of
4, so we still need a CIC in the FPGA.
Oussama.
Matt
On 7/11/06, *Eric Blossom* <[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>> wrote:
On Mon, Jul 10, 2006 at 08:22:29PM -0700, Oussama Sekkat wrote:
> Hello everybody,
>
> I am still a beginner in the project so bare with me if my
questions have
> obvious answers.
> I was looking at the verilog code for usrp_std.v module. that
module
> containes the tx_chain.v module which uses a module called
phase_acc.
Actually, if you look at that line, you'll see that it's within an
`ifdef that's not enabled. Take a look again ;)
> I am not sure what this later module does? It takes as inputs
(among others) a
> 7bit serial address and 32 bit serial data and outputs the 32bit
phase.
> Does anyone have any idea what that module does and what its
purpose is in
> the tx_chain?
If enabled, this code would implement digital upconversion in the
FPGA, instead of using the DUC in the AD9862. N.B., this code hasn't
been tested in something like a couple of years and may have suffered
bit rot. [Definitely. The FPGA register definitions that would have
been required to use it have been removed...]
Eric
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