Digitizer to output: the computational pipeline


Overview of spectrometer computations:

   The pdev spectrometer uses fixed point arithmetic to compute the spectrum. It has a number of registers  to control the signal gain during this computation. These registers need to be set to maximize the dynamic range of the processing.

    The dynamic range is determined by:

The processing stages and registers in pdev:

    Figure 1 is a simplified outline of the pdev processing steps. The text highlighted in blue are the programmable registers. The shift register values are specified in bits eg.: 3 bits would let you shift 0 to 7 multiplying/dividing the value by 2^0 to 2^7 (1 to 128).
The steps include:

pdev signal path


Testing the gain settings:  (top)

    The gain settings were tested by working backwords from an integrated spectra. At each step the current values were measured or computed. The setup for the data set was:
The plots show the power, voltages levels for the processing (.ps) (.pdf):

Conclusions: (working from the digitizer input up to the spectra)   (top)

processing: x101/071002/spcToRms.pro    ~phil/hardware/pdev/misc/pdevgain.gif for figure.

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