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Re: [Discuss-gnuradio] Why 4 ADC's?
From: |
Jeff Brower |
Subject: |
Re: [Discuss-gnuradio] Why 4 ADC's? |
Date: |
Thu, 19 Jul 2007 11:31:10 -0500 |
Eric-
> > > The LFRX has two separate antenna inputs, supplied to Vin-A and
> > > Vin-B. These are not I-Q data. USRP board FPGA logic would apply
> > > one mixer or two (30 MHz or less).
> >
> > [...]
> >
> > > The RFX2400 mixes with a 2.4 GHz osc and creates one set of I-Q 65
> > > MHz range signals, +/-I on Vin-A and +/-Q on Vin-B. To get baseband
> > > signals, the logic has to apply two mixers.
> >
> > The FPGA DDC logic uses a single but *complex* mixer to do frequency
> > conversion of the signal from the ADCs. That is, it treats the data
> > from Vin-A and Vin-B as a complex number in I and Q format, and
> > multiplies this complex number by a complex sinusoid of a configurable
> > frequency. This is very different from having two mixers.
>
> In fact the routing from the ADCs to the inputs of the DDCs is
> controlled by the input mux in the FPGA. You can route any ADC
> into any DDC input, or you can stick a constant zero into the Q input
> (details below).
>
> The _default_ wiring depends on the software that controls the given
> daughterboard. By default the Basic Rx and LF RX daughterboard code
> treats the two inputs as two separate real inputs (not I & Q), one
> into DDC 0, one into DDC 1. You can easily override this by calling
> u.set_mux(...) The RFX-* daughterboards treat the signals as I & Q,
> since that's the only configuration that makes sense given the
> quadrature output of the RFX-* boards.
Thanks, that's very helpful. I thought there would have to be a way to form
real-valued data for the low-end daughtercards, but hadn't found it yet.
-Jeff
> See http://gnuradio.org/trac/wiki/UsrpRfxDiagrams
>
> /*!
> * \brief Set input mux configuration.
> *
> * This determines which ADC (or constant zero) is connected to
> * each DDC input. There are 4 DDCs. Each has two inputs.
> *
> * <pre>
> * Mux value:
> *
> * 3 2 1
> * 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
> * +-------+-------+-------+-------+-------+-------+-------+-------+
> * | Q3 | I3 | Q2 | I2 | Q1 | I1 | Q0 | I0 |
> * +-------+-------+-------+-------+-------+-------+-------+-------+
> *
> * Each 4-bit I field is either 0,1,2,3
> * Each 4-bit Q field is either 0,1,2,3 or 0xf (input is const zero)
> * All Q's must be 0xf or none of them may be 0xf
> * </pre>
> */
> bool set_mux (int mux);
>
> Eric [ decloaking after vacation ;) ]
- [Discuss-gnuradio] Why 4 ADC's?, Ian Larsen, 2007/07/17
- Message not available
- Re: [Discuss-gnuradio] Why 4 ADC's?, Ian Larsen, 2007/07/18
- Re: [Discuss-gnuradio] Why 4 ADC's?, Roshan Baliga, 2007/07/18
- Re: [Discuss-gnuradio] Why 4 ADC's?, Johnathan Corgan, 2007/07/18
- Re: [Discuss-gnuradio] Why 4 ADC's?, Jeff Brower, 2007/07/18
- Re: [Discuss-gnuradio] Why 4 ADC's?, Roshan Baliga, 2007/07/18
- Re: [Discuss-gnuradio] Why 4 ADC's?, Jeff Brower, 2007/07/19
- Re: [Discuss-gnuradio] Why 4 ADC's?, Johnathan Corgan, 2007/07/19
- Re: [Discuss-gnuradio] Why 4 ADC's?, Jeff Brower, 2007/07/19
- Re: [Discuss-gnuradio] Why 4 ADC's?, Eric Blossom, 2007/07/19
- Re: [Discuss-gnuradio] Why 4 ADC's?,
Jeff Brower <=
- Re: [Discuss-gnuradio] Why 4 ADC's?, Ian Larsen, 2007/07/18
- Re: [Discuss-gnuradio] Why 4 ADC's?, Jeff Brower, 2007/07/19