lmf380 National Semiconductor Corporation, lmf380 Datasheet

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lmf380

Manufacturer Part Number
lmf380
Description
Triple One-third Octave Switched-capacitor Active Filter
Manufacturer
National Semiconductor Corporation
Datasheet
C 1995 National Semiconductor Corporation
LMF380 Triple One-Third Octave
Switched-Capacitor Active Filter
General Description
The LMF380 is a triple one-third octave filter set designed
for use in audio audiological and acoustical test and mea-
surement applications Built using advanced switched-ca-
pacitor techniques the LMF380 contains three filters each
having a bandwidth equal to one-third of an octave in fre-
quency By combining several LMF380s each covering a
frequency range of one octave a filter set can be imple-
mented that encompasses the entire audio frequency range
while using only a small fraction of the number of compo-
nents and circuit board area that would be required if a con-
ventional active filter approach were used The center fre-
quency range is not limited to the audio band however
Center frequencies as low as 0 125 Hz or as high as 25 kHz
are attainable with the LMF380
The center frequency of each filter is determined by the
clock frequency The clock signal can be supplied by an
external source or it can be generated by the internal oscil-
lator using an external crystal and two capacitors Since the
LMF380 has an internal clock frequency divider (
an output pin for the half-frequency clock signal a single
clock oscillator for the top-octave LMF380 becomes the
master clock for the entire array of filters in a multiple
LMF380 application
Simplified Block Diagram
TL H 11123
d
2) and
Accuracy is enhanced by close matching of the internal
components the ratio of the clock frequency to the center
frequency is typically accurate to
gain and stopband attenuation are guaranteed over the full
temperature range
Features
Y
Y
Y
Key Specifications
Y
Y
Applications
Y
Y
Y
Three bandpass filters with one-third octave center fre-
quency spacing
Choice of internal or external clock
No external components other than clock or crystal and
two capacitors
Passband gain accuracy Better than 0 7 dB over
temperature
Supply voltage range
Real-Time Audio Analyzers (ANSI Type E Class II)
Acoustical Instrumentation
Noise Testing
g
2V to
TL H 11123 – 1
g
g
7 5V or
0 5% and passband
RRD-B30M115 Printed in U S A
November 1995
a
4V to
a
14V

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lmf380 Summary of contents

Page 1

... LMF380 Triple One-Third Octave Switched-Capacitor Active Filter General Description The LMF380 is a triple one-third octave filter set designed for use in audio audiological and acoustical test and mea- surement applications Built using advanced switched-ca- pacitor techniques the LMF380 contains three filters each ...

Page 2

... ESD Susceptibility (Note Operating Ratings Temperature Range LMF380CIN LMF380CIV LMF380CIJ 300 C LMF380CMJ a Supply Voltage (V 215 C 220 C Clock Input Frequency The following specifications apply for all other limits apply for T MIN MAX Typical ...

Page 3

... the current at that pin should be limited The 20 mA Jmax the number given in the Absolute Maximum Ratings whichever is lower D Jmax the LMF380N when board-mounted ...

Page 4

Typical Performance Characteristics Power Supply Current vs Power Supply Voltage Negative Output Swing vs Load Resistance Offset Voltage vs Supply Voltage Power Supply Current Positive Output Swing vs Temperature vs Load Resistance Positive Output Swing Negative Output Swing vs Temperature ...

Page 5

... CLK CLK The three filters in an LMF380 cover a full octave in fre- quency so that by using several LMF380s with clock fre- quencies separated by a factor complex audio pro- gram can be analyzed for frequency content over a range of several octaves To facilitate this the CLK OUT pin of the ...

Page 6

... LMF380’s output (see Figure 4 ) INPUT IMPEDANCE The LMF380’s input pins are connected directly to the inter- nal biquad filter sections The input impedance is purely ca- pacitive and is approximately each input pin in- ...

Page 7

... Typical Applications FIGURE 3 Complete one-third octave filter set for the entire audio frequency range Ten LMF380s provide the thirty bandpass filters required for this function Power supply connections and bypass capacitors are not shown Pin numbers are for the dual-in-line package TL H 11123 – ...

Page 8

... The output of this first LMF60 – 100 drives the inputs of the fifth sixth and seventh LMF380s The sev- enth LMF380 has a 15 625 kHz clock so aliasing will begin to become a problem around 15 2 kHz With a sixth-order 2 5 kHz low-pass filter preceding this circuit the attenuation ...

Page 9

Typical Applications (Continued) (a) FIGURE 4 Examples of detectors for audio signals (a) Half-wave peak detector (b) Half-wave average detector (c) Full-wave peak detector (d) Full-wave average detector All diodes are 1N914 or 1N4148 Input RC low-pass filters attenuate clock ...

Page 10

Typical Applications (Continued) FIGURE 5 LED display using LM3915 bar graph driver The input voltage range is 2V full-scale with 3 dB per step TL H 11123 – ...

Page 11

... Physical Dimensions inches (millimeters) Order Number LMF380C1J or LMF380CMJ Dual-In-Line Package (J) NS Package Number J16A Dual-In-Line Package (N) Order Number LMF380CIN NS Package Number N16E 11 ...

Page 12

... National does not assume any responsibility for use of any circuitry described no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications Plastic Chip Carrier Package (V) Order Number LMF380CIV NS Package Number V20A 2 A critical component is any component of a life ...

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