HSP43124PC-33 datasheet(8/17 Pages) INTERSIL

8 / 17 page

NOTE: Figure 8 shows the loading of a data sample, X0, such

that it will be multiplied by a mix factor designated by M0. For

mix factor bit widths which are less than the input bit width,

SYNCMX may be asserted before SYNCIN if desired.

If the mix factor is generated by the Weaver Modulator ROM,

the mix factor must be speciﬁed on MXIN and SYNCMX one

SYNCIN before that which precedes the target data word

(see Figure 9).

Filter Compute Engine

The Filter Compute Engine centers around a multiply

accumulator which is used to perform the sum-of-products

required for a variety of ﬁltering conﬁgurations. These

conﬁgurations include a cascade of up to 5 halfband ﬁlters, a

single symmetric ﬁlter of up to 256 taps, a single asymmetric

ﬁlter of up to 128 taps, or a cascade of halfband ﬁlters

followed by a programmable ﬁlter. The ﬁlter conﬁguration is

speciﬁed by programming the Filter Conﬁguration Register

(see Table 1).

The cascade of up to ﬁve halfband ﬁlters is an efﬁcient

decimating ﬁlter structure. Each ﬁxed coefﬁcient ﬁlter in the

chain introduces a decimation of two, and the aggregate

decimation rate of the entire halfband ﬁltering stage is given

by:

Thus, a cascade of 3 halfband ﬁlters would decimate the

input sample stream by a factor of 8.

Figure 10A is a block diagram of the halfband ﬁlter section.

The normalized frequencies for each halfband stage is

labeled. Figure 10B is an illustration of a cascaded ﬁlter

composed of ﬁve halfband ﬁlters. The ﬁnal stage ﬁlter output

is clocked at FCLK/32. Since the output of each ﬁlter is at

half the rate of the input, the ﬁve halfband ﬁlter passband

characteristics can be viewed on a single plot whose X axis

is normalized to the ﬁlter output clock rate. Notice that all

halfband ﬁlters, by design, have 120dB passbands that are

less than the output rate divided by 2. Since the alias proﬁle

is well below -120dB in the ﬁlter passband, alias concerns

are eliminated. The frequency responses of the ﬁve ﬁlters

are presented graphically in Figure 10C and in tabular form

in Table 3. Notice that the 6dB passband bandwidth (F =

0.25) is identical for all ﬁve halfband ﬁlters. The width of the

transition band, however, is different for each ﬁlter. The

transition band for the ﬁfth halfband ﬁlter, HB5, is the

narrowest while that for the ﬁrst halfband ﬁlter, HB1, is the

widest. The cascade of the halfband ﬁlters always

terminates with HB5 and is preceded by ﬁlters in order of

increasing transition bandwidth. For example, if the

HSP43124 is conﬁgured to operate with three halfbands, the

chain of ﬁlters would consist of HB3 followed by HB4 and

terminated with HB5. If only one halfband is selected, HB5 is

used.

DIN

SCLK

SYNCIN

SYNCMX

MXIN

LSB

MSB

LSB

MSB

FIGURE 8. DATA/MIX FACTOR SYNCHRONIZATION FOR

SERIALLY INPUT MIX FACTORS

SYNC LEADS DATA

DIN

SCLK

SYNCIN

SYCNMX/

MXIN

MSB

LSB

FIGURE 9. DATA/MIX FACTOR SYNCHRONIZATION WEAVER

MODULATOR MIX FACTORS

SYNC LEADS DATA

DECHB = 2

(NUMBER OF HALFBAND FILTERS SELECTED)

(EQ. 1)

HSP43124

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