TL H 10354
LMF90
4th-Order
Elliptic
Notch
Filter
December 1994
LMF90
4th-Order Elliptic Notch Filter
General Description
The LMF90 is a fourth-order elliptic notch (band-reject) filter
based on switched-capacitor techniques No external com-
ponents are needed to define the response function The
depth of the notch is set using a two-level logic input and
the width is programmed using a three-level logic input Two
different notch depths and three different ratios of notch
width to center frequency may be programmed by connect-
ing these pins to V
a
ground or V
b
Another three-level
logic pin sets the ratio of clock frequency to notch frequen-
cy
An internal crystal oscillator is provided Used in conjunction
with a low-cost color TV crystal and the internal clock fre-
quency divider a notch filter can be built with center fre-
quency at 50 Hz 60 Hz 100 Hz 120 Hz 150 Hz or 180 Hz
for rejection of power line interference Several LMF90s can
be operated from a single crystal An additional input is pro-
vided for an externally-generated clock signal
Features
Y
Center frequency set by external clock or on-board
clock oscillator
Y
No external components needed to set response char-
acteristics
Y
Notch width attenuation and clock-to-center-frequency
ratio independently programmable
Y
14 pin 0 3
wide package
Key Specifications
Y
f
0
Range
0 1 Hz to 30 kHz
Y
f
0
accuracy over full temperature range (max)
1 5%
Y
Supply voltage range
g
2V to
g
7 5V or 4V to 15V
Y
Passband Ripple (typ)
0 25 dB
Y
Attenuation at f
0
(typ)
39 dB or 48 dB (selectable)
Y
f
CLK
f
0
100 1 50 1 or 33 3 1
Y
Notch Bandwidth (typ)
0 127 f
0
0 26 f
0
or 0 55 f
0
Y
Output offset voltage (max)
120 mV
Applications
Y
Automatic test equipment
Y
Communications
Y
Power line interference rejection
Typical Connection
60 Hz Notch Filter
TL H 10354 1
Connection
Diagram
Dual-In-Line and Small
Outline Packages
TL H 10354 2
Top View
Order Number LMF90CCN
LMF90CIWM
LMF90CCWM LMF90CIJ
LMF90CCJ LMF90CIN
LMF90CMJ or
LMF90CMJ 883
See NS Package Number
J14A M14B or N14A
C1995 National Semiconductor Corporation
RRD-B30M115 Printed in U S A