TLH7509

February 1995

LM1865 Advanced FM IF System

General Description

Reduced external component cost improved performance

and additonal functions are key features to the LM1865 FM

IF system The LM1865 is designed for use in electronically

tuned radio applications It contains both deviation and sig-

nal level stop circuitry in addition to an open-collector stop

output The LM1865 generates a reverse AGC voltage (ie

decreasing AGC voltage with increasing signal)

Features

Y

On-chip buffer to provide gain and terminate two ce-

ramic filters

Y

Low distortion 01% typical with a single tuned quadra-

ture coil for 100% modulation

Y

Broad off frequency distortion characteristic

Y

Low THD at minimum AFT offset

Y

Meter output proportional to signal level

Y

Stop detector with open-collector output

Y

Adjustable signal level mutestop threshold controlled

either by ultrasonic noise in the recovered audio or by

the meter output

Y

Adjustable deviation mutestop threshold

Y

Separate time constants for signal level and deviation

mutestop

Y

Dual threshold AGC eliminates need for localdistance

switch and offers improved immunity from third order in-

termodulation products due to tuner overload

Y

User control of both AGC thresholds

Y

Excellent signal to noise ratio AM rejection and system

limiting sensitivity

Block Diagram

Order Number LM1865M

or LM1865N

See NS Package Number

M20B or N20A

TLH7509 – 1

FIGURE 1

C1995 National Semiconductor Corporation

RRD-B30M115Printed in U S A