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Today's Topics:
1. USB2 <-> fast ADC & DAC (Andy Green)
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Date: Tue, 27 May 2003 15:58:50 +0100
From: Andy Green <address@hidden>
To: address@hidden
Subject: [Discuss-gnuradio] USB2 <-> fast ADC & DAC
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Hi folks -
My friend Milosch and I are interested to make a generic USB2 <->
fast=20
ADC and DAC board, based around a Cypress FX2 chip, a FIFO and a
fast=20
ADC and/or DAC. We are both experienced engineers and expect no=20
difficulty with the digital side.
This is intended to be a completely generic USB-powered baseband=20
module with all processing done back at the PC in realtime. Milosch=20
did some tests and found it was possible to transfer 20MBytes/sec=20
like this with latencies of under 2mS over USB2. It is this
transfer=20
rate which is the limiting factor, not the conversion rates on the=20
ADC or DACs.
We have a use for this design already, but we are interested to see
if=20
with some guidence from yourselves it can be made to be of use to
the=20
gnu radio project too, since it will be cheap, small and selfpowered.
=20
Some areas that we would welcome opinions on:
- I assumed that a baseband-only device like this is in fact useful=20
for this project. However I see existing designs are interested in=20
outputting modulated RF at ~30MHz via an FPGA or DSP. Is a=20
baseband-only device even useful?
- What resolution and speed ADC is needed to be considered useful? =20
We can transfer up to ~10Msps at 16 bits simplex, or ~5Msps at 16=20
bits duplex (ie, simultaneous tx and rx). The choice of ADC and DAC=20
specs has obvious impact on the cost.
- What kind of analogue IO is most useful? 1Vp-p 50ohm input and=20
output? Transformer coupled? Filtered?
- I saw on the list AGC mentioned, is this desirable on this kind
of=20
module to have programmable attenuation or amplification?
- Has this kind of Native Signal Processing ((c)Intel 199x) at
these=20
kind of datarates been tried before? Considering that on a modern
PC=20
SSE2 or MMX is available, what are the opinions about being able to=20
have the CPU process data in realtime for common modulation schemes?
Any advice is welcome :-)
=2D -Andy
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