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LF2242JC33

12/16-bit Half-Band Interpolating/Decimating Digital Filter

LOGIC Devices 

DEVICES INCORPORATED

LF2242

12/16-bit Half-Band Interpolating/

Decimating Digital Filter

FIGURE 1. FREQUENCY RESPONSE OF FILTER

0

–10

–20

–30

Controls

INT — Interpolation Control

When INT is LOW and DEC is HIGH

(Table 1), the device internally forces

every other incoming data sample to

zero. This effectively halves the input

data rate and the output amplitude.

–40

–50

–60

–70

–80

0

0.1ƒS

0.2ƒS

0.3ƒS

0.4ƒS

0.5ƒS

DEC — Decimation Control

When DEC is LOW and INT is HIGH

(Table 1), the output register is strobed on

every other rising edge of CLK (driven at

half the clock rate), decimating the output

data stream.

FREQUENCY (NORMALIZED)

TABLE 1. MODE SELECTION

INT DEC

MODE

SIGNAL DEFINITIONS

Power

VCC and GND

+5 V power supply. All pins must be

connected.

Inputs

SI11–0 — Data Input

12-bit two’s complement data input

port. Data is latched into the register on

the rising edge of CLK. The LSB is SI0

(Figure 2).

0

0 Pass-through*

0

1 Interpolate

1

0 Decimate

1

1 Pass-through*

*Input and output registers run at full

clock rate

Clock

Outputs

CLK — Master Clock

SO15-0 Data Output

The rising edge of CLK strobes all regis-

ters. All timing specifications are refer-

enced to the rising edge of CLK.

SYNC — Synchronization Control

Incoming data is synchronized by hold-

ing SYNC HIGH on CLKN, and then by

bringing SYNC LOW on CLKN+1 with

the first word of input data. SYNC is held

LOW until resynchronization is desired,

or it can be toggled at half the clock rate.

For interpolation (INT = LOW), input

data should be presented at the first ris-

ing edge of CLK for which SYNC is LOW

and then at every alternate rising edge of

CLK thereafter. SYNC is inactive if DEC

and INT are equal (pass-through mode).

The current 16-bit result is available on

the SO15-0 outputs. The LF2242’s limiter

ensures that a valid full-scale (7FFF

positive or 8000 negative) output will be

generated in the event of an internal

overflow. The LSB is SO0 (Figure 2).

Video Imaging Products

2

08/16/2000–LDS.2242-K

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