LM1865 Advanced FM IF System
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)
Y
Y
Y
Meter output proportional to signal level
Stop detector with open-collector output
Adjustable signal level mute stop threshold controlled
either by ultrasonic noise in the recovered audio or by
the meter output
Adjustable deviation mute stop threshold
Separate time constants for signal level and deviation
mute stop
Dual threshold AGC eliminates need for local distance
switch and offers improved immunity from third order in-
termodulation products due to tuner overload
User control of both AGC thresholds
Excellent signal to noise ratio AM rejection and system
limiting sensitivity
Y
Y
Features
Y
Y
Y
On-chip buffer to provide gain and terminate two ce-
ramic filters
Low distortion 0 1% typical with a single tuned quadra-
ture coil for 100% modulation
Broad off frequency distortion characteristic
Low THD at minimum AFT offset
Y
Y
Y
Y
Block Diagram
Order Number LM1865M
or LM1865N
See NS Package Number
M20B or N20A
FIGURE 1
TL H 7509 鈥?1
C
1995 National Semiconductor Corporation
TL H 7509
RRD-B30M115 Printed in U S A