hsp50214a Intersil Corporation, hsp50214a Datasheet - Page 18

• Manufacturer Part Number: hsp50214a
• Description: Programmable Downconverter
• Manufacturer: Intersil Corporation

Depending on the number of halfbands used, PROCCLK
must operate at a minimum rate above the input sample rate,
F
ber of multiplies for each of the halfband filter stages. The fil-
ter calculations take 3, 4, 5, 6, and 7 multiplies per input for
HB1, HB2, HB3, HB4, and HB5 respectively. If we keep the
assumption that f
Equation 10 shows the minimum ratio needed.
f
where
HB1 = 1 if this section is selected and 0 if it is bypassed;
HB2 = 1 if this section is selected and 0 if it is bypassed;
HB3 = 1 if this section is selected and 0 if it is bypassed;
HB4 = 1 if this section is selected and 0 if it is bypassed;
HB5 = 1 if this section is selected and 0 if it is bypassed;
T = number of Halfband Filters Selected. The range for T is
from 0 to 5.
Examples of PROCCLK Rate Calculations
Suppose we enable HB1, HB3, and HB5. Using Figure 16,
HB1= 1, HB3 = 1, and HB5 = 1. Since stage 2 and stage 4
are not used, HB2 and HB4 = 0. PROCCLK must operate
faster than (7x2+5x4+3x8)/8 = 7.25 times faster than F
If all five halfbands are used, then PROCCLK must operate at
(7x2+6x4+5x8+4x16+3x32)/32 = 7.4375 times faster than F
255-Tap Programmable FIR Filter
The Programmable FIR filter can be used to implement real
filters with even or odd symmetry, using up to 255 filter taps,
or complex filters with up to 64 taps. The FIR filter takes
advantage of symmetry in coefficients by summing data
samples that share a common coefficient, prior to multiplica-
tion. In this manner, two filter taps are calculated per multiply
accumulate cycle. Asymmetric filters cannot share common
coefficients, so only one tap per multiply accumulate cycle is
calculated. The filter can be effectively bypassed by setting
the coefficient C
Additionally, the Programmable FIR filter provides for deci-
mation factors, R, from 1 to 16. The processing rate of the
Filter Compute Engine is PROCCLK. As a result, the fre-
quency of PROCCLK must exceed a minimum value to
ensure that a filter calculation is complete before the result is
required for output. In configurations which do not use deci-
mation, one input sample period is available for filter calcula-
tion before an output is required. For configurations which
employ decimation, up to 16 input sample periods may be
available for filter calculation.
PROCCLK
S
, to the halfband. This relationship depends on the num-
/f
S
(6)(HB4)(2
(5)(HB3)(2
(4)(HB2)(2
(3)(HB1)(2
([(7)(HB5)(2
0
= 1 and all other coefficients, C
S
is the input sampling frequency, then
(HB4 + HB5)
(HB3+HB4+HB5)
(HB2+HB3+ HB4+HB5)
(HB1+HB2+HB3+HB4+HB5)
HB5
)+
)+
)+
)+
N
)]/2
= 0.
(EQ. 10))
HSP50214A
T
S
.
S
.
18
For real filter configurations, use Equation 11 to calculate the
number of taps available at a given input filter sample rate.
for real filters, and
for complex filters, where floor is defined as the integer por-
tion of a number; PROCCLK is the compute clock; F
the FIR input sample rate; R = Decimation Factor; SYM = 1
for symmetrical filter, 0 for asymmetrical filter; ODD# = 1 for
an odd number of filter taps, 0 = an even number of taps.
Use Equation 12 to calculate the maximum input rate.
for real filters, and
F
for complex filters, where floor[x], PROCCLK, F
Decimation Factor, SYM, and ODD# are defined as in Equa-
tion 11.
Use Equation 13 to calculate the maximum output sample
rate for both real and complex filters.
The coefficients are 22 bits and are loaded using writes to
Control Words 128 through 255 (see Microprocessor Write
Section). For real filters, the same coefficients are used by I
and Q paths. If the filter is configured as a symmetric filter
using Control Word 17, Bit 9, then coefficients are loaded
starting with the center coefficient in Control Word 128 and
proceeding to last coefficient in Control Word 128+n. The fil-
ter symmetry type can be set to even or odd symmetric, and
the number of filter coefficients can be even or odd, as illus-
trated in Figure 20. Note that complex filters can also be
realized but are only allowed to be asymmetric. Only the
coefficients that are used need to be loaded.
TAPS
TAPS
F
F
SAMP
SAMP
FIR OUT
=
=
=
=
SYM)
floor (PROCCLK
=
floor PROCCLK
PROCCLK
SYM ODD#
PROCCLK R
F
SAMP
–
SYM ODD#
R
R
1
F
F
R
+
R
SAMP
SAMP
+
SYM
+
floor Taps
floor Taps 2
R
R
–
–
R
R
2]
1 +
+
SAMP
(EQ. 11A)
(EQ. 11B)
(EQ. 12A)
(EQ. 12B)
SAMP
(EQ. 13)
, R =
=