3-203

In the polyphase implementation, the input data stream

feeds even and odd tap filters running at the input sample

rate. The interpolated sample stream is derived by

multiplexing the output of each polyphase branch into a

single data stream at twice the input sample rate. As in the

Decimate by Two example, the even or odd tap filters are

comprised of the even or odd indexed coefficients from the

original transversal filter.

The operation of the HSP43216 in Interpolate by Two mode

is analogous to the polyphase example above. In this mode

the internal data flow is routed as shown in Figure 11A and

Figure 11B. The different data flows depend on the selection

of internal or external multiplexing via INT/EXT. In this mode,

data input through AIN0-15 is fed to the even and odd

polyphase branches of the filter processor. The output of

each branch is multiplexed together to generate the output

data stream at the interpolated rate.

NOTE: The output of

each polyphase branch is scaled by two to compensate

for the attenuation of one half caused by interpolation.

C0 C1 C2 C3 C4 C5 C6

..,X2,X1,X0

Y(1) = X0(C0)+0(C1)+X1(C2)+0(C3)+X2(C4)+0(C5)+X3(C6)

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

...,Y1,Y0

2

..X1,0,X0,0

7 TAP HALFBAND FILTER

Y(3) = X1(C0)+0(C1)+X2(C2)+0(C3)+X3(C4)+0(C5)+X4(C6)

Y(2) = 0(C0)+X1(C1)+0(C2)+X2(C3)+0(C4)+X3(C5)+0(C6)

FIGURE 9. TRANSVERSAL IMPLEMENTATION OF

INTERPOLATE BY TWO HALFBAND FILTER

C0 C2 C4 C6

...,X2,X1,X0

Y0 = X0(C1)+X1(C3)+X2(C5)

Y1 = X0(C0)+X1(C2)+X2(C4)+X3(C6)

..,Y4,Y2,Y0

C1 C3 C5

R

E

G

ODD TAP FILTER

EVEN TAP FILTER

M

U

X

..,Y5,Y3,Y1

..,Y2,Y1,Y0

Y2 = X1(C1)+X2(C3)+X3(C5)

FIGURE 10. POLYPHASE IMPLEMENTATION OF INTERPOLATE

BY TWO HALFBAND FILTER

FIGURE 11A. DATA FLOW DIAGRAM FOR INTERPOLATE BY 2 FILTER MODE (INT/EXT = 1)

FIGURE 11B. DATA FLOW DIAGRAM FOR INTERPOLATE BY 2 FILTER MODE (INT/EXT = 0)

EVEN TAP

FILTER

ODD TAP

FILTER

AIN0-15

AOUT0-15

OEA

R

E

G

R

E

G

R

E

G

R

E

G

R

E

G

R

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N

D

F

M

T

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E

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R

E

G

R

E

G

R

E

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1

1

2

2

R

E

G

M

U

X

†

†

†

†

†

†

EVEN TAP

FILTER

AIN0-15

AOUT0-15

R

E

G

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E

G

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E

G

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T

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1

1

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E

G

R

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1

ODD TAP

FILTER

OEB

1

BOUT0-15

R

N

D

F

M

T

R

E

G

R

E

G

OEA

GROUP DELAY 19

PIPELINE DELAY 2-35

GROUP DELAY 19

PIPELINE DELAY 19

R

E

G

R

E

G

HSP43216