HSP43124 View Datasheet(PDF) - Intersil
Part Name
Description
Manufacturer
HSP43124 Datasheet PDF : 18 Pages
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HSP43124
The coefficient set for each of the halfband filters is given in
Table 4. These values are the 32-bit, two’s complement,
integer representation of the filter coefficients. Scaling these
values by 2-31 yields the fractional two’s complement
coefficients used to achieve unity gain in the Filter Processor.
If a specific frequency response is desired, a programmable
FIR filter may be activated. The filter compute engine takes
advantage of symmetry in FIR coefficients is by summing
data samples sharing a common coefficient prior to
multiplication. In this manner, two filter taps are calculated
per multiply accumulate cycle. If an asymmetric filter is
specified, only one tap per multiply accumulate cycle is
calculated.
The processing rate of the Filter Compute Engine is
proportional to FCLK. As a result, the frequency of FCLK
must exceed a minimum value to insure that a filter
calculation is complete before the result is required for
output. In configurations which do not use decimation, one
input sample period is available for filter calculation before
an output is required. For configurations which employ
decimation, up to 256 input sample periods may be available
for filter calculation. The following equation specifies the
minimum FCLK rate required for configurations which use
the programmable filter as an FIR filter.
Min FCLK
=
⎧
⎪
⎨
D-----E--F--C--S--H----B--
(
TAPS/(2*DECFIR
)
+
HBCLKS
+
1
)
⎪
⎩
or
at
least 14 F S
when
Halfbands
are
used
(EQ. 2)
In this equation FS is the input sample rate (SCLK/# Bits in
SER word), TAPS is the number of taps in the FIR filter (0 to
256), DECFIR is the decimation rate of the programmable
FIR (1 to 8), HBCLKS is a compute clock factor based on the
number of halfband filters in the configuration (see Table 5),
and DECHB is the aggregate decimation rate for the
cascade of halfband filters (see Table 5). For example, if the
input sample rate is 800kHz, a 128 tap FIR filter with no
decimation is selected, and a cascade of 2 halfband filters is
used, calculate the minimum FCLK rate as follows:
Min
FCLK
=
⎪⎪⎧⎝⎛
⎨
8----0---0---4-k---H-----z--⎠⎞
⎛
⎝
⎛
⎝
-1-2--2--1-8--⎠⎞
+ 33 + 1⎠⎞
⎪(200kHz)[64 + 33 + 1] = 19.6MHz
⎩⎪or at least 14 (800kHz) = 11.2MHz
(EQ. 3)
Thus, the Min FCLK is 19.6MHz.
NOTE: For configurations in which the halfband filters are
used, the FCLK rate must exceed 14FS.
The longest length FIR filter realizable for a particular
configuration is determined by solving the above equation
for TAPS. The resulting expression is given below.
Max TAPS = 2DECFIR((FCLK/FS)DECHB - HBCLKS - 1) (EQ. 4)
The maximum throughput sample rate may be specified by
solving the above equation for FS. The resulting equation is
Max FS = FCLK*DECHB /(TAPS/(2*DECFIR) + HBCLKS + 1). (EQ. 5)
NOTE: For configurations using filters with asymmetric coeffi-
cients, the term TAPS in the above equations should be multi-
plied by two in order to determine the correct FCLK.
The Filter Compute Engine is synchronized with an incoming
data stream by asserting the FSYNC input. When this input
is sampled low by the rising edge of FCLK, the Compute
Engine is reset, and the data word following the next
assertion of SYNCIN is recognized as the first data sample
input to the filter structure.
NORMALIZED
FREQUENCY
0.000000
0.007812
0.015625
0.023438
0.031250
0.039062
0.046875
0.054688
0.062500
0.070312
0.078125
0.085938
0.093750
TABLE 3. FREQUENCY RESPONSE OF HALFBAND FILTERS
HALFBAND
#1
HALFBAND
#2
HALFBAND
#3
HALFBAND
#4
-0.000000
0.000000
0.000000
-0.000000
0.000000
-0.000000
-0.000000
-0.000000
-0.000113
-0.000000
-0.000000
-0.000000
-0.000677
-0.000006
-0.000000
-0.000000
-0.002243
-0.000052
-0.000000
-0.000000
-0.005569
-0.000227
-0.000000
-0.000000
-0.011596
-0.000719
-0.000001
0.000000
-0.021433
-0.001859
-0.000009
-0.000000
-0.036333
-0.004165
-0.000041
-0.000000
-0.057670
-0.008391
-0.000149
-0.000001
-0.086916
-0.015557
-0.000448
-0.000012
-0.125619
-0.026983
-0.001175
-0.000066
-0.175382
-0.044301
-0.002767
-0.000258
HALFBAND
#5
-0.000000
-0.000000
-0.000000
-0.000000
-0.000000
0.000000
-0.000000
-0.000000
-0.000000
-0.000000
-0.000000
-0.000000
-0.000000
10
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