February 1995
LM1865 Advanced FM IF System
Y
Meter output proportional to signal level
General Description
Y
Y
Stop detector with open-collector output
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).
Adjustable signal level mute/stop threshold, controlled
either by ultrasonic noise in the recovered audio or by
the meter output
Y
Y
Adjustable deviation mute/stop threshold
Separate time constants for signal level and deviation
mute/stop
Y
Dual threshold AGC eliminates need for local/distance
switch and offers improved immunity from third order in-
termodulation products due to tuner overload
Features
Y
On-chip buffer to provide gain and terminate two ce-
ramic filters
Y
Y
User control of both AGC thresholds
Y
Low distortion 0.1% typical with a single tuned quadra-
ture coil for 100% modulation.
Excellent signal to noise ratio, AM rejection and system
limiting sensitivity
Y
Broad off frequency distortion characteristic
Y
Low THD at minimum AFT offset
Block Diagram
Order Number LM1865M
or LM1865N
See NS Package Number
M20B or N20A
TL/H/7509–1
FIGURE 1
C
1995 National Semiconductor Corporation
TL/H/7509
RRD-B30M115/Printed in U. S. A.