TL H 5185
LM1863
AM
Radio
System
for
Electronically
Tuned
Radios
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
TL H 5185 1
Order Number LM1863M
See NS Package Number M20B
C1995 National Semiconductor Corporation
RRD-B30M115 Printed in U S A
Absolute Maximum Ratings
Supply Voltage
16V
Package Dissipation (Note 1)
1 7W
Storage Temperature Range
b
55 C to
a
150 C
Operating Temperature Range
0 C to
a
70 C
Soldering Information
Small Outline Package
Vapor Phase (60 sec)
215 C
Infrared (15 sec)
220 C
See AN-450 ``Surface Mounting Methods and Their Effect
on Product Reliability'' for other methods of soldering sur-
face mount devices
Electrical Characteristics
(Test Circuit T
A
e
25 C V
a e
12V SW1
e
Position 1 SW2
e
Position 2 unless indicated otherwise)
Parameter
Conditions
Min
Typ
Max
Units
STATIC CHARACTERISTICS
Supply Current
V
IN
e
0 mV
8 3
12 5
mA
Pin 16 Regulator Voltage
5 6
V
Operating Voltage Range
(See Note 2)
7
16
V
Pin 3 Leakage Current
V
IN
e
0 mV
0 1
m
A
Pin 9 Low Output Voltage
V
IN
e
0 mV SW2
e
Position 1
15
V
Pin 17 Output Voltage
V
IN
e
0 mV
0
V
DYNAMIC CHARACTERISTICS (f
MOD
e
1 kHz f
IN
e
1 MHz M
e
0 3)
Maximum Sensitivity
V
IN
For V
AUDIO
e
6 mVrms
7 5
m
V
20 dB Quieting Sensitivity
V
IN
for 20 dB S N in Audio
15
30
m
V
Maximum Signal to Noise Ratio
V
IN
e
10 mV
40
54
dB
Total Harmonic Distortion
V
IN
e
10 mV
26
%
Total Harmonic Distortion
V
IN
e
10 mV M
e
0 8
63
2
%
Audio Output Level
V
IN
e
10 mV
80
120
160
mVrms
Overload Distortion
V
IN
e
50 mV M
e
0 8
7 5
%
Meter Output Voltage
V
IN
e
100 mV
0 5
V
Meter Output Voltage
V
IN
e
10 mV
4 6
V
Local Oscillator Output Level
(See Note 3) SW1
e
Position 1
100
147
mVrms
on Pin 19
Local Oscillator Output Level
(See Note 3) SW1
e
Position 2
125
mVrms
on Pin 19
Stop Detector Valid Station
V
IN
e
10 mV difference between
Frequency Window
the two frequencies at which
2 5
4
5 5
kHz
Pin 9
k
1V SW2
e
Position 1
Stop Detector Valid Station
Find V
IN
for which Pin 9
l
1V
8
16
70
m
Vrms
Signal Level Threshold
SW2
e
Position 1
RF AGC Threshold
Find V
IN
that produces
3
6
10
mVrms
10 mA of current into Pin 3
Pin 3 Low Output Level
V
IN
e
30 mV
0 1
V
Pin 9 Leakage Current
V
IN
e
30 mV
0 1
m
A
Pin 17 Output Resistance
V
IN
e
10 mV
825
X
Note 1
Above T
A
e
25 C derate based on T
j (MAX)
e
150 C and i
jA
e
85 C W
Note 2
All data sheet specifications are for V
a e
12V and may change slightly with supply
Note 3
The local oscillator level at Pin 19 is identical to the level at Pin 18 since Pin 19 is an emitter follower off of Pin 18
2
Test Circuit
TL H 5185 2
Typical Performance Characteristics
(From Test Circuit)
TL H 5185 9
TL H 5185 10
TL H 5185 11
3
Application Circuit
LM1863
AM
ETR
Radio
TLH5185
8
4
Performance Characteristics of Applications Circuit
TL H 5185 12
TL H 5185 13
TL H 5185 14
TL H 5185 15
Cross modulation is
measured using the
following dummy an-
tenna
The following procedure was used to measure cross modulation
1 Tune the radio to the center frequency of interest and tune V
GEN
to this same frequency
2 Set at 0 dB audio reference with V
GEN
e
10 mV RMS and 30% AM mod f
MOD
e
1 kHz
3 Remove the modulation from V
GEN1
and set the level of V
GEN1
4 Set the modulation level of V
GEN2
e
80% at f
MOD
e
1 kHz and tune V
GEN2
g
40 kHz away from
center frequency
5 Increase the level of V
GEN2
until
b
40 dB of audio is recovered The level of V
GEN2
is the cross
modulation measurement
TL H 5185 16
Additional Performance Information
THD for 80% modulation for f
MOD
e
1 kHZ at
V
GEN
e
1V is 0 5%
V
GEN
e
10 mV is 0 4%
Tweet
k
2% at all input levels
Typical time for valid stop indication
k
50 ms
Note
Tweet is an audio tone produced by the 2nd and 3rd harmonic of the IF beating against the received
signal It is measured as an equivalent modulation level ie 30% tweet has the same amplitude at the
detector as a desired signal with 30% modulation
5
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