LF2242 LODEV [LOGIC Devices Incorporated], LF2242 Datasheet

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LF2242

Manufacturer Part Number
LF2242
Description
12/16-bit Half-Band Interpolating/ Decimating Digital Filter
Manufacturer
LODEV [LOGIC Devices Incorporated]
Datasheet

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DEVICES INCORPORATED
FEATURES
LF2242 B
40 MHz Clock Rate
Passband (0 to 0.22f
Ripple:
Stopband (0.28f
Rejection: 59.4 dB
User-Selectable 2:1 Decimation or
1:2 Interpolation
12-bit Two’s Complement Input
and 16-bit Output with
User-Selectable Rounding, 8- to
16-Bits
User-Selectable Two’s Complement
or Inverted Offset Binary Output
Formats
Three-State Outputs
Replaces TRW/ Raytheon/
Fairchild TMC2242
Package Styles Available:
• 44-pin PLCC, J-Lead
• 44-pin PQFP
DEVICES INCORPORATED
SI
CLK
11–0
12
0.02 dB
LOCK
S
D
to 0.5f
IAGRAM
S
TO ALL REGISTERS
)
INTERPOLATION
S
CIRCUIT
)
3
12
The LF2242 is a linear-phase, half-
band (low pass) interpolating/
decimating digital filter that, unlike
intricate analog filters, requires no
tuning. The LF2242 can also signifi-
cantly reduce the complexity of
traditional analog anti-aliasing pre-
filters without compromising the
signal bandwidth or attenuation. This
can be achieved by using the LF2242
as a decimating post-filter with an
A/D converter and by sampling the
signal at twice the rate needed.
Likewise, by using the LF2242 as an
interpolating pre-filter with a D/A
converter, the corresponding analog
reconstruction post-filter circuitry can
be simplified.
The coefficients of the LF2242 are
fixed, and the only user programming
required is the selection of the mode
(interpolate, decimate, or pass-
through) and rounding. The asyn-
chronous three-state output enable
control simplifies interfacing to a bus.
Data can be input into the LF2242 at a
rate of up to 40 million samples per
second. Within the 40 MHz I/O limit,
the output sample rate can be one-
half, equal to, or two times the input
DESCRIPTION
55-TAP
FILTER
FIR
12/16-bit Half-Band Interpolating/
INT DEC
1
SYNC
TCO
AND LIMIT
CIRCUIT
12/16-bit Half-Band Interpolating/
ROUND
Decimating Digital Filter
RND
3
3
2–0
16
sample rate. Once data is clocked in,
the 55-value output response begins
after 7 clock cycles and ends after 61
clock cycles. The pipeline latency
from the input of an impulse response
to its corresponding output peak is 34
clock cycles.
The output data may be in either
two’s complement format or inverted
offset binary format. To avoid
truncation errors, the output data is
always internally rounded before it is
latched into the output register.
Rounding is user-selectable, and the
output data can be rounded from 16
bit values down to 8 bit values.
DC gain of the LF2242 is 1.0015
(0.0126 dB) in pass-through and
decimate modes and 0.5007 (–3.004
dB) in interpolate mode. Passband
ripple does not exceed 0.02 dB from
0 to 0.22f
greater than 59.4 dB from 0.28f
0.5f
response of the filter is –6 dB at 0.25f
Full compliance with CCIR Recom-
mendation 601 (–12 dB at 0.25f
be achieved by cascading two devices
serially.
Decimating Digital Filter
Video Imaging Products
3
DECIMATION
S
(Nyquist frequency). The
CIRCUIT
S
with stopband attenuation
LF2242
OE
16
08/16/2000–LDS.2242-K
LF2242
SO
S
S
15–0
) can
to
S
.

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LF2242 Summary of contents

Page 1

... The asyn- chronous three-state output enable control simplifies interfacing to a bus. Data can be input into the LF2242 at a rate million samples per second. Within the 40 MHz I/O limit, the output sample rate can be one- ...

Page 2

... CLK. The LSB is SI (Figure 2). Outputs SO Data Output 15-0 The current 16-bit result is available on the SO outputs. The LF2242’s limiter 15-0 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 SO (Figure 2). 0 ...

Page 3

... When OE is HIGH, the 15-0 outputs are in a high-impedance state Video Imaging Products 08/16/2000–LDS.2242-K LF2242 ...

Page 4

... Min 4 (Note 3) Ground V V (Note 12 (Note 12) (Notes 5, 6) (Note 25° MHz 25° MHz A 4 LF2242 Decimating Digital Filter + 0 0 Voltage Supply Min Typ Max Unit 2.4 V 0.4 V 2.0 V ...

Page 5

... DEC) HROUGH ODE N HIGH IMPEDANCE t t DIS ENA 5 12/16-bit Half-Band Interpolating/ Decimating Digital Filter LF2242– 33 Min Max N+1 Video Imaging Products 08/16/2000–LDS.2242-K LF2242 25 Min Max N+2 ...

Page 6

... SO 15-0 OE 12/16-bit Half-Band Interpolating/ M (INT = 0, DEC = 1) ODE N HIGH IMPEDANCE DIS ENA M (INT = 1, DEC = 0) ODE N HIGH IMPEDANCE t t DIS ENA 6 LF2242 Decimating Digital Filter N+1 N N+2 Video Imaging Products 08/16/2000–LDS.2242 ...

Page 7

... ENA OE 1 Measured V with I = –10mA and Measured V with I = –10mA and Video Imaging Products 08/16/2000–LDS.2242-K LF2242 test, DIS C IRCUIT EVELS t DIS 3.5V Vth 0 0 Vth = 10mA OL = 10mA OL ...

Page 8

... S CREENING S CREENING 8 LF2242 Decimating Digital Filter Top View Plastic Quad Flatpack (Q4) LF2242QC33 LF2242QC25 Video Imaging Products 08/16/2000–LDS.2242-K GND ...

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