TLH10354

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 03

wide package

Key Specifications

Y

01 Hz to 30 kHz

Y

15%

Y

Supply voltage range

g

Y

Passband Ripple (typ)

025 dB

Y

39 dB or 48 dB (selectable)

Y

1001 501 or 3331

Y

Notch Bandwidth (typ)

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

TLH10354 – 1

Connection

Diagram

Dual-In-Line and Small

Outline Packages

TLH10354 – 2

Top View

Order Number LMF90CCN

LMF90CIWM

LMF90CCWM LMF90CIJ

LMF90CCJ LMF90CIN

LMF90CMJ or

LMF90CMJ883

See NS Package Number

J14A M14B or N14A

C1995 National Semiconductor Corporation

RRD-B30M115Printed in U S A