3848
DUAL-CONVERSION AM RECEIVER
DISCONTINUED PRODUCT
-- FOR REFERENCE ONL
Y
MIX 2 E
B
13
8
9
10
24
25
26
STOP
MIX 1 IN
CRYSTAL
AGC RATE 2
MIX 2 OUT
DET
WB
AGC
MIX 1 OUT
A
MIX 1 OUT
B
WB AGC OUT
OSC COIL
OSC BUFFER
LOW-LEVEL
GROUND
WB AGC 2 IN
MIX 2 IN
Dwg. PS-012-1
V
REF
REFERENCE
1
2
3
4
IF OUT
DETECTOR
SUPPLY
AUDIO OUT
HIGH-LEVEL
GROUND
IF BIAS
DECOUPLE
V
CC
AFC OUT
IF
AGC (MUTE)
V
REG
REGULATOR
6
7
27
28
MIX 2 OUT
FSI
5
29
B
A
30
31
32
11
22
23
WB AGC 1 IN
MIX 2 E
B
21
RESET
MIX 2
BYPASS
14
15
16
17
18
19
20
12
SUB
3848
Dwg. No. PS-012-1
DUAL-CONVERSION AM RECEIVER
Providing the AM signal processing functions for an electronically
tuned AM receiver (ETR), the A3848EEQ includes two balanced
mixers, a crystal local oscillator, an L/C-tuned local oscillator, oscillator
buffer, IF amplifier, AM detector, scan control detectors, and a switch-
able voltage regulator. This dual-conversion device typically mixes the
incoming RF up to a first IF of 10.7 MHz, then down to 450 kHz, and
then detects the audio. The addition of a JFET matched to a whip
antenna, RF low-pass filter, IF selectivity, and audio stages gives a
complete AM radio which can be used in automotive receivers. The
frequency-detecting stop circuit is also capable of recovering narrow-
band FM, making it useful for scanners or weather band radio applica-
tions. Two AGC and field-strength indicator modes provide special
features for scanning.
The A3848EEQ uses the dual criteria of frequency and amplitude
for establishing a valid stop. Tuning accuracy (frequency criterion) is
established by evaluating phase shift across the detector coil. The
circuitry is similar to that used in FM discriminators. Because this
detection system is phase operated, it remains effective even in the
presence of strong signals, which can cause false stops in systems
using narrow-band filters. The amplitude criterion for stop is deter-
mined by evaluating the IF level. It includes a unique circuit that
removes the effect of the AGC action. This allows the AGC tuning
components to be selected for low-frequency audio performance
without compromising scanning speed.
In the normal AGC mode (AGC RESET low), a slow, narrow-band
field-strength indicator (FSI) is provided for controlling signal-depen-
dent functions such as stereo blending. A fast AGC mode (AGC
RESET high) resets the AGC holding capacitors to maximum gain.
This mode allows cataloging station strengths quickly during a band
sweep.
This AM signal processor is packaged in a rectangular, 32-lead,
plastic, leaded chip carrier (PLCC) for surface-mount applications and
is rated for operation over the temperature range of -40
C to +105
C
are available on special order.
FEATURES
s
Low Noise Figure
s
Field-Strength Indicator
s
Balanced Mixers
s
Buffered Oscillator
s
High Dynamic Range First Mixer
s
Fast Scan Mode
Always order by complete part number: A3848EEQ .
ABSOLUTE MAXIMUM RATINGS
Supply Voltage, V
CC
. . . . . . . . . . . . . . 12 V
Package Power Dissipation, P
D
. . . . 1.2 W
Operating Temperature Range,
T
A
. . . . . . . . . . . . . . . -40
C to +105
C
Storage Temperature Range,
T
S
. . . . . . . . . . . . . . . -65
C to +150
C
Data Sheet
27121.15
3848
DUAL-CONVERSION AM RECEIVER
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
Limits
Characteristic
Symbol
Test Conditions
Min
Typ
Max
Units
Supply Current
I
CC
I
2
, V
in
= 0
--
50
65
mA
I
2
, V
in
= 0, V
27
= 0 (Muted)
--
1.0
6.0
mA
Sensitivity
V
in
V
out
= 50 mV
--
6.0
10
V
Usable Sensitivity
V
in
S + N/N = 20 dB
--
14
21
V
Recovered Audio
V
out
165
215
265
mV
Total Harmonic Dist.
THD
Mod = 90%
--
0.4
2.0
%
Oscillator Output
V
o
V
17
80
120
--
mV
Stop Output Voltage
V
STP
V
8
, V
in
= 0
4.7
5.0
--
V
V
8
, Mod = 0%
--
0.10
0.16
V
Stop Sensitivity
V
stp
V
12
= 2.5 V, Mod = 0%
30
45
60
V
Stop Bandwidth
BW
STP
V
8
= 2.5 V, = 0%
5.0
6.5
8.0
kHz
Wide-Band AGC
V
AGC
V
in
= 0
5.0
6.7
8.0
V
V
in
= 11 mV, Mod = 0%
3.7
5.0
--
V
V
in
= 26 mV, Mod = 0%
--
--
1.0
V
V
FSI
V
in
= 0
--
0.1
0.4
V
V
in
= 30
V, Mod = 0%
0.25
0.60
1.05
V
V
in
= 100
V, Mod = 0%
1.1
1.6
2.2
V
V
in
= 1 mV, Mod = 0%
1.8
2.5
3.2
V
V
in
= 10 mV, Mod = 0%
3.1
3.7
4.4
V
V
FSI
V
in
= 0
--
--
0.5
V
V
in
= 30
V, Mod = 0%
0.9
1.1
1.5
V
V
in
= 100
V, Mod 0%
1.3
1.6
2.0
V
V
in
= 1 mV, Mod = 0%
2.3
2.9
3.5
V
V
in
= 10 mV, Mod = 0%
2.5
3.7
4.0
V
Overload
V
in
V
out
= 3% THD, Mod = 90%
60
100
--
mV
First Mixer (Note 2)
350
450
--
mV
-3dB Limiting
V
in
Mod = 3 kHz peak deviation
--
12
--
V
IF Output Voltage
V
out
V
in
= 1 mV
200
250
320
mV
FM Recovered Audio
V
out
V
7
, Mod = 3 kHz peak deviation
--
380
--
mV
Signal to Noise Ratio
S+N/N
V
in
= 1 mV
50
53
--
dB
V
in
= 10 mV
53
56
--
dB
AGC Figure of Merit
FOM
Ref. at V
in
= 10 mV, V
in
for V
out
= -10 dB
7.0
10
14
V
ELECTRICAL CHARACTERISTICS at T
A
= +25
C, V
CC
= 10 V, f
o
= 1 MHz, f
if1
= 10.7 MHz,
f
if2
= 450 kHz, V
in
= 10 mV; f
m
= 1 kHz , Mod = 30% (except as noted).
Field-Strength
Indicator
Output Voltage
(unmodulated,
AGC Reset Low)
Field-Strength
Indicator
Output Voltage
(unmodulated,
AGC Reset High)
Continued next page...
W
Copyright 1993, Allegro MicroSystems, Inc.
3848
DUAL-CONVERSION AM RECEIVER
ELECTRICAL CHARACTERISTICS at T
A
= +25
C, V
CC
= 10 V, f
o
= 1 MHz, f
if1
= 10.7 MHz,
f
if2
= 450 kHz, V
in
= 10mV; f
m
= 1 kHz, Mod = 30% (except as noted) (concluded)
Limits
Characteristic
Symbol
Test Conditions
Min
Typ
Max
Units
Regulator Voltage
V
REG
V
6
4.7
5.0
5.3
V
V
6
, V
27
= 0 (Muted)
--
0
0.3
V
Reference Voltage
V
REF
V
15
3.2
3.4
3.6
V
NOTES: 1. Typical data is for design information only.
2. Attenuate MIXER 1 output with 50
load on mixer coil secondary, V
out
=3% THD, Mod = 90%
Allegro MicroSystems, Inc. reserves the right to make, from time to
time, such departures from the detail specifications as may be required
to permit improvements in the design of its products.
The information included herein is believed to be accurate and
reliable. However, Allegro MicroSystems, Inc. assumes no responsibil-
ity for its use; nor for any infringements of patents or other rights of third
parties which may result from its use.
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