3-202

If internal multiplexing is selected (INT/EXT = 1), the input data

stream is decomposed into even and odd samples internally by

the processing elements operating at one half of the input CLK

(see elements marked by “†” in Figure 7A). In this mode, the

Data Flow Controller routes data samples input through AIN0-

15 to upper and lower processing legs with a one sample

relative delay. Since a new data sample is clocked into either of

the processing legs at CLK/2, each leg processes a data

stream comprised of every other input sample, and the one

sample relative delay of each leg’s input forces the even

samples to be clocked into one leg while the odd samples are

clocked into the other. The user may choose which sample gets

routed to the upper (even) processing leg by asserting SYNC.

Specifically, a sample input on the CLK following the assertion

of SYNC will be routed to the upper processing leg as shown in

Figure 8. With internal multiplexing, the minimum pipeline delay

on the upper processing leg is 14 CLK’s and the pipeline delay

on the bottom leg is 47 CLK’s. The filtered and decimated data

stream is held on AOUT0-15 for 2 CLK’s.

If external multiplexing is selected (INT/EXT = 0), a

demultiplex function is required off chip to break the input

data into even and odd sample streams for input through

AIN0-15 and BIN0-15. In this mode, the Data Flow Controller

routes the even and odd sample streams directly to the

following processing elements which are all running at the

input CLK rate. This allows the device to perform decimate

by two filtering on signals sampled at up to twice the

maximum CLK rate of the device (104 MSPS). With external

multiplexing, the minimum pipeline delay through the upper

processing leg is 9 CLK’s and the pipeline delay through the

lower processing leg is 26 CLK’s as shown in Figure 7B. In

this mode, SYNC has no effect on part operation.

NOTE: For proper operation, the samples demultiplexed

to the AIN0-15 input must precede those input to the

BIN0-15 input in sample order. For example, given a data

sequence x0, x1, x2 and x3, the demultiplex function would

route x0 and x2 to AIN0-15 and x1 and x3 to BIN0-15.

Interpolate By 2 Filter Mode (Mode1-0 = 01)

As with the Decimate by Two mode the concept of operation

for the Interpolate by Two Filter mode is more easily

understood by comparing a 7 tap transversal filter

implementation to the equivalent polyphase implementation.

The transversal implementation is shown in Figure 9.

By inspecting filter outputs in Figure 9, it is seen that the

even indexed outputs are the result of the sum-of-products

for the odd coefficients, and the odd indexed outputs are the

result of the sum-of-products for the even coefficients. This

computational partitioning is evident in the polyphase

implementation shown in Figure 10.

FIGURE 7A. DATA FLOW DIAGRAM FOR DECIMATE BY 2 FILTER MODE (INT/EXT = 1)

FIGURE 7B. DATA FLOW DIAGRAM FOR DECIMATE 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

E

G

R

N

D

F

M

T

R

E

G

R

E

G

R

E

G

R

E

G

1

1

1

1

†

+

†

†

†

††

EVEN TAP

FILTER

AIN0-15

AOUT0-15

R

E

G

R

E

G

R

E

G

R

N

D

F

M

T

R

E

G

R

E

G

R

E

G

E

G

1

1

R

E

G

R

E

G

R

E

G

R

E

G

R

E

G

1

ODD TAP

FILTER

OEA

1

BIN0-15

+

GROUP DELAY 19

PIPELINE DELAY 2-35

GROUP DELAY 19

PIPELINE DELAY 19

R

012

CLK

SYNC

INPUTS DESIGNATED AS EVEN ARE PROCESSED ON THE UPPER

LEG, INPUTS DESIGNATED AS ODD ARE PROCESSED ON THE

LOWER LEG.

AIN0-15

FIGURE 8. DATA SYNCHRONIZATION WITH PROCESSING

LEGS (INT/EXT = 1)

EVEN

ODD

EVEN

HSP43216