HSP43216(1999) 查看數據表（PDF） - Intersil

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HSP43216
(Rev.:1999)

Halfband Filter

Intersil 

HSP43216

TABLE 5. OUTPUT ROUNDING CONTROL

RND

2-0

ROUND FUNCTION

000 Round output to 8 bits, AOUT15-8 and BOUT15-8,

zero lower bits.

001 Round output to 9 bits, AOUT15-7 and BOUT15-7,

zero lower bits.

010 Round output to 10 bits, AOUT15-6 and BOUT15-6,

zero lower bits.

011 Round output to 11 bits, AOUT15-5 and BOUT15-5,

zero lower bits.

100 Round output to 12 bits, AOUT15-4 and BOUT15-4,

zero lower bits.

101 Round output to 14 bits, AOUT15-2 and BOUT15-2,

zero lower bits.

110 Round output to 16 bits, AOUT15-0 and BOUT15-0.

111 Zero all outputs.

Operational Modes

Decimate By 2 Filter Mode (Mode1-0 = 00)

The concept of operation for Decimate by Two Filter mode is

most easily understood by comparing the 7 tap transversal

filter implementation to the equivalent polyphase

implementation. The transversal implementation is shown in

Figure 5.

X3,X2,X1,X0

...,Y1,Y0

..,Y4,Y2,Y0

2

C0 C1 C2 C3 C4 C5 C6

Y(0) = X0(C0)+X1(C1)+X2(C2)+X3(C3)+X4(C4)+X5(C5)+X6(C6)

† Y(1) = X1(C0)+X2(C1)+X3(C2)+X4(C3)+X5(C4)+X6(C5)+X7(C6)

Y(2) = X2(C0)+X3(C1)+X4(C2)+X5(C3)+X6(C4)+X7(C5)+X8(C6)

† Y(3) = X3(C0)+X4(C1)+X5(C2)+X6(C3)+X7(C4)+X8(C5)+X9(C6)

† Indicates samples discarded by decimation process

FIGURE 5. TRANSVERSAL IMPLEMENTATION OF DECI-

MATE BY 2 HALFBAND FILTER

In the polyphase implementation, the input data is broken into

even and odd sample streams which are processed by a set

of polyphase filters running at one half of the input data rate.

These filters are designated as even or odd tap filters

depending upon whether the coefficients were derived from

the even or odd indexed coefficients of the original transversal

filter. This architecture only produces the outputs which are

not discarded by the decimation process. NOTE: Since the

only non-zero tap for a halfband filter is the center tap,

the Odd Tap Filter reduces to a delay and multiply

operation.

The operation of the HSP43216 in Decimate by Two mode is

analogous to the polyphase implementation in Figure 6. In

this mode, the internal data paths are routed as shown in

Figure 7A and Figure 7B. The different data flows depend on

whether internal or external multiplexing has been selected

using the INT/EXT control input. In either case, an input data

stream is decomposed into even and odd sample streams

which are then routed to the even and odd tap polyphase

filters. The output of each polyphase filter is summed and

output via AOUT0-15.

EVEN TAP FILTER

...,X4,X2,X0

C0 C2 C4 C6

ODD TAP FILTER

..,Y2,Y1,Y0

+

...,X5,X3,X1 R

E

G

C1 C3 C5

Y(0) = X0(C0)+X1(C1)+X2(C2)+X3(C3)+X4(C4)+X5(C5)+X6(C6)

Y(1) = X2(C0)+X3(C1)+X4(C2)+X5(C3)+X6(C4)+X7(C5)+X8(C6)

FIGURE 6. POLYPHASE IMPLEMENTATION OF DECIMATE

BY 2 HALFBAND FILTER

By inspecting the sum-of-products for the decimated output

in Figure 5, it is seen that even indexed input samples are

always multiplied by the even filter coefficients and the odd

samples are always multiplied by the odd coefficients. This

computational partitioning is realized in the polyphase

implementation shown in Figure 6.

3-201

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