TLH5185

May 1989

LM1863 AM Radio System for

Electronically Tuned Radios

General Description

The LM1863 is a high performance AM radio system intend-

ed primarily for electronically tuned radios Important to this

application is an on-chip stop detector circuit which allows

for a user adjustable signal level threshold and center fre-

quency stop window The IC uses a low phase noise level-

controlled local oscillator

Low phase noise is important for AM stereo which detects

phase noise as noise in the L-R channel A buffered output

for the local oscillator allows the IC to directly drive a phase

locked loop synthesizer The IC uses a RF AGC detector to

gain reduce an external RF stage thereby preventing over-

load by strong signals An improved noise floor and lower

THD are achieved through gain reduction of the IF stage

Fast AGC settling time which is important for accurate stop

detection and excellent THD performance are achieved

with the use of a two pole AGC system Low tweet radiation

and sufficient gain are provided to allow the IC to also be

used in conjunction with a loopstick antenna

Features

Y

Low supply current

Y

Level-controlled low phase noise local oscillator

Y

Buffered local oscillator output

Y

Stop circuitry with adjustable stop threshold and adjust-

able stop window

Y

Open collector stop output

Y

Excellent THD and stop time performance

Y

Large amount of recovered audio

Y

RF AGC with open collector output

Y

Meter output

Y

Compatible with AM stereo

Block Diagram

TLH5185 – 1

Order Number LM1863M

See NS Package Number M20B

C1995 National Semiconductor Corporation

RRD-B30M115Printed in U S A