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LM3820 AM Radio System
LM3820 AM Radio System
February 1989
General Description
The LM3820 is a 3-stage AM radio IC consisting of an RF
amplifier, oscillator, mixer, IF amplifier, AGC detector, and
zener regulator.
The device was originally designed for use in slug-tuned
auto radio applications, but is also suitable for capacitortuned portable radios.
The LM3820 is an improved replacement for the LM1820.
Connection Diagram
Dual-In-Line Package
Order Number LM3820N
See NS Package Number N14A
Circuit Schematic
Features
Y
Input protection diodes
Y
Good control on sensitivity
Y
Improved S/N and tweet
Y
Versatile building-block approach
Y
Gain-controlled RF stage
Y
Cascode IF amplifier
Y
Regulated supply
Y
Pin compatible with LM1820
TL/H/7967– 1
TL/H/7967– 2
C
1995 National Semiconductor Corporation RRD-B30M115/Printed in U. S. A.
TL/H/7967
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Absolute Maximum Ratings
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales
Office/Distributors for availability and specifications.
Power Dissipation (Note 1) 1200 mW
Supply Voltage 16V
Electrical Characteristics (
Figure 1
,T
e
A
Symbol Parameter Conditions Min Typ Max Units
I
S
V
Z
Supply Current No RF Input 12 18 24 mA
Internal Zener Voltage 7.0 7.5 8.0 V
Input Sensitivity fe1 MHz, 30% Mod 400 Hz
Measure RF Input Level for
10 mV Audio Output with
Tuning Peaked
Signal to Noise Ratio fe1 MHz, 30% Mod 1 kHz
a
N)/N at Audio Output 22 28 Ð dB
(S
with 100 mV RF Input
Overload Distortion fe1 MHz, 90% Mod 1 kHz
THD at Audio Output Ð 6 10 %
with 30 mV RF Input
Note 1: Above T
e
25§C, derate based on T
A
J(Max)
e
150§C and i
e
JA
Current into Supply Terminal (Pin 3) 35 mA
Operating Temperature Range
Storage Temperature Range
Lead Temperature (Soldering, 10 sec.) 260
e
25§C, V
6V unless noted)
S
15 35 70 mV
100§C/W.
b
25§Ctoa85§C
b
65§Ctoa150§C
Typical Applications
C
§
*100 mV RF INPUT is equivalent to approx. 1 mV/meter field strength. See Applications Information for coil specifications. TL/H/7967– 3
FIGURE 1. Capacitor-Tuned Test Fixture
2
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Applications Information
The circuit shown in
point for portable radio designs. Loopstick antenna L1 is
used in place of L0, and the RF amplifier is used with a
resistor load to drive the mixer. A double tuned circuit at the
output of the mixer provides selectivity, while the remainder
of the gain is provided by the IF section, which is matched to
the diode through a unity turns ratio transformer. R
be used in place of C
tor and provide more recovered audio.
Figure 1
is recommended as a starting
to bypass the internal AGC detec-
AGC
AGC
may
An AM automobile radio design is shown in
Figure 2
. Tuning
of both the input and the output of the RF amplifier and the
mixer is accomplished with variable inductors. Better selectivity is obtained through the use of double tuned interstage
transformers. Input circuits are inductively tuned to prevent
microphonics and provide a linear tuning motion to facilitate
push-button operation.
Coil specifications for
Figure 1
are as follows:
PCB Layout for
Figure 1
3
Circuit
TL/H/7967– 4
TL/H/7967– 5
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Applications Information (Continued)
TRANSFORMERS
e
T1: C
130 pF primary & secondary
primary to secondary tap ratioÐ30:1
e
60
Q
couplingÐcritical
FIGURE 2. Slug-Tuned Auto Radio
Schematic
Reference
L0, L2 RWO-6A6255
T1 RRC-3A6426N
T2 RRC-3A6427A
T3 RZC-1A6425A
*Toko America
1250 Feehanville Drive
Mount Prospect, IL 60056
(312) 297-0070
FIGURE 3. Representative Part Numbers
for the Coils of
4
Toko* Part Number
Figure 1
e
130 pF primary & secondary
T2: C
primary tap ratioÐ8.5:1
secondary tap ratioÐ8.5:1
e
60
Q
couplingÐcritical
TL/H/7967– 6
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5
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Physical Dimensions inches (millimeters)
LM3820 AM Radio System
Molded Dual-In-Line Package (N)
Order Number LM3820N
NS Package Number N14A
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DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL
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systems which, (a) are intended for surgical implant support device or system whose failure to perform can
into the body, or (b) support or sustain life, and whose be reasonably expected to cause the failure of the life
failure to perform, when properly used in accordance support device or system, or to affect its safety or
with instructions for use provided in the labeling, can effectiveness.
be reasonably expected to result in a significant injury
to the user.
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