LF43881 查看數據表（PDF） - LOGIC Devices

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LF43881

8 x 8-bit Digital Filter

LOGIC Devices 

DEVICES INCORPORATED

LF43881

8 x 8-bit Digital Filter

TABLE 1. DECIMATION MODE SELECTION

DCM1 DCM0 Decimation Function

0

0

Decimation registers not used

0

1

One decimation register used (decimation by one-half)

1

0

Two decimation registers used (decimation by one-third)

1

1

Three decimation registers used (decimation by one-fourth)

SIGNAL DEFINITIONS

Power

VCC and GND

+5 V power supply. All pins must be

connected.

Clock

TABLE 2. REGISTER AND ACCUMULATOR CLEARING

CLK — Master Clock

ERASE RESET

0

0

0

1

1

0

1

1

Clearing Effect

All accumulators and all registers are cleared

Only the accumulator addressed by ADR2-0 is cleared

All registers are cleared (accumulators are not cleared)

No clearing occurs, internal state remains the same

OUTPUT STAGE DESCRIPTION

The 26-bit adder contained in the

output stage can add the contents of

any filter cell accumulator (selected by

ADR2-0) with the 18 most significant

bits of the output buffer. The result is

stored back into the output buffer.

The complete operation takes only one

clock cycle. The eight least significant

bits of the output buffer are lost.

The Zero multiplexer is controlled by

the SHADD input signal. This allows

selection of either the 18 most signifi-

cant bits of the output buffer or all

zeros for the adder input. When

SHADD is LOW, all zeros will be

selected. When SHADD is HIGH, the

18 most significant bits of the output

buffer are selected enabling the shift-

and-add operation. SHADD is

latched and delayed internally by one

clock cycle.

The output multiplexer is also con-

trolled by the SHADD input signal.

This allows selection of either a filter

cell accumulator, selected by ADR2-0,

or the output buffer to be output to

the SUM25-0 bus. Only the 26 least

significant bits from either a filter cell

accumulator or the output buffer are

output on SUM25-0. If SHADD is

LOW during two consecutive clock

cycles (low during the current and

previous clock cycle), the output

multiplexer selects the contents of a

filter cell accumulator addressed by

ADR2-0. Otherwise, the output

multiplexer selects the contents of the

output buffer.

If the same address remains on the

ADR2-0 inputs for more than one clock

cycle, SUM25-0 will not change to

reflect any updates to the addressed

cell accumulator. Only the result from

the first selection of the cell (first clock

cycle) will be output. This allows the

interface of slow memory devices

where the output needs to be active

for more than one clock cycle. Normal

FIR operation is not affected because

ADR2-0 is changed sequentially.

NUMBER SYSTEMS

Data and coefficients can be repre-

sented as either unsigned or two's

complement numbers. The TCS and

TCCI inputs determine which of the

two formats is to be used. All values

are represented as 9-bit two's comple-

ment numbers internally. The value

of the ninth bit is determined by the

number system selected. The ninth bit

is a sign extended bit when the two's

complement mode is chosen. When

the unsigned mode is chosen, the

ninth bit is zero.

The rising edge of CLK strobes all

registers. All timing specifications are

referenced to the rising edge of CLK.

Inputs

DIN7-0 — Data Input

8-bit data is latched into the X register

of each filter cell simultaneously. The

TCS signal selects the appropriate

data format type. The DIENB signal

enables loading of the data.

CIN7-0 — Coefficient Input

8-bit coefficients are latched into the C

register of Filter Cell 0. The TCCI

signal selects the appropriate coeffi-

cient format type. The CIENB signal

enables loading of the coefficients.

Outputs

SUM25-0 — Data Output

The 26-bit result from an individual

filter cell will appear when ADR2-0 is

used to select the filter cell result.

SHADD in conjunction with ADR2-0 is

used to select the output from the

shift-and-add output stage.

COUT7-0 — Coefficient Output

The 8-bit coefficient output from

Filter Cell 7 can be connected to the

CIN7-0 coefficient input of the same

LF43881 to recirculate the coefficients.

COUT7-0 can also be connected to the

CIN7-0 of another LF43881 to cascade

the devices. The COENB signal

enables the output of the coefficients.

Video Imaging Products

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08/16/2000–LDS.43881-J

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