GC1115_06 Datasheet, PDF (28/82 Pages) Texas Instruments – Crest Factor Reduction Processor

GC1115
SLWS144C – FEBRUARY 2005 – REVISED JUNE 2006
18
I
Q
18
Function
Generator
(I, Q, mag^2)
SNAP_MAXVAL
16
16
min & max
range check
16
SNAP_MINVAL
SNAP_SCALE
16
10
−
x
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HISTOGRAM
INDEX
10
Histogram bin
update
(fetch bin count,
increment,
store inc’d count)
Histogram bins
(1k x 32 bits)
Figure 11. Snapshot RAM Histogram Operation
• SNAP_MINVAL: minimum value of interest (-32768..+32767)
• SNAP_MAXVAL: maximum value of interest (-32768..+32767)
• SNAP_SCALE: a 16-bit multiplier that scales the 16-bit (value – SNAP_MINVAL) into the 10-bit range
0..1023.
In C pseudo-code, the GC1115 histogram index calculation and bin update is performed as follows:
if ( (funcGen[i] >= SNAP_MINVAL) && (funcGen[i] <= SNAP_MAXVAL) ) {
j
= funcGen[i] SNAP_MINVAL;
index = int(j * SNAP_SCALE);
index &= 0x3FF;
hist[index]++
}
The minimum histogram index will never be less than 0, while the maximum histogram index should never
exceed 1023. The SNAP_MINVAL and SNAP_MAXVAL values allow GC1115 users to bracket specific sample
ranges of interest, while ignoring values outside of this range. The SNAP_SCALE multiplier then maps the range
of interest into the available histogram bins (0..1023).
In histogram mode, the GC1115 snapshot RAMs collect statistics on the frequency of occurrence of certain
sample or magnitude-squared values. Since the GC1115 contains two snapshot RAMs, these statistics can be
used to simultaneously monitor the signal at two different stages of processing (such as at the input and at the
output). After a time, the histograms stored in RAM A and RAM B are read by the microprocessor or DSP, which
allows derived values (such as CCDF) to be obtained from the histogram bin counts.
Snapshot RAMs can be individually cleared (i.e. all entries set to zero) via control bits in the
SNAP_A_CONTROL and SNAP_B_CONTROL registers. Snapshot RAMs must be cleared prior to histogram
processing in order to zero all histogram counts.
Table 13 below shows how the snapshot RAM memory is used in capture and histogram modes. The addresses
in Table 13 are those that appear in the SNAP_A_ADDRESS or SNAP_B_ADDRESS registers.
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