On Sun, Feb 28, 2010 at 02:57:45PM +0000, Tim Pearce wrote: > Hi, > > I've been having a look at usrp2/host/lib/copiers.cc and the schematics to > try and work out if the units mean anything. > > As far as I can tell the LTC2284 ADC is set up to use the +-1V input range > and output 14bits as a twos complement. > > From the datasheet/the maths I think the ADC is thus giving possible outputs > of -8192 to 8191 (i.e ~ +- 2^13) where -8192 represents -1V and 8191 > represents 1V-0.000122V. > > Where I'm confused is with copy_u2_16sc_to_host_32fc the integers are scaled > to produce floats where -32768 and 32768 (i.e using the full 16bits of the > storage variable) are mapped to -1.0 and 1.0 respectively. Is there a reason > for this? I haven't tried to look at what the FPGA is doing with this data > yet..
The output from the ADC is run through a digital downconverter in the FPGA. In general, the output of that process is between -32768 to 32767. If you're looking for "volts", you'll need to calibrate the entire signal path. That will depend on the daughterboard, it's gain, temperature, etc. A bit of searching of the list archives will turn up quite a bit of discussion on this topic. Eric _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
