A3848: Dual-Conversion AM Receiver

3848
Data Sheet
27121.15
3848
DUAL-CONVERSION AM RECEIVER
DECOUPLE
AUDIO OUT
HIGH-LEVEL
GROUND
1
DETECTOR
SUPPLY
3
2
IF OUT
4
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 switchable 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 narrowband FM, making it useful for scanners or weather band radio applications. Two AGC and field-strength indicator modes provide special
features for scanning.
FSI
5
REGULATOR
6
AFC OUT
7
31 IF BIAS
30
32
T
C
U Y
D L
O
N
R
P EO
D
C
E
N
U
E
N R
I
E
T
N EF
O
R
C
IS OR
D F
—
VCC
SUB
V REG
DET
29
MIX 2 OUTB
28
IF
27
AGC (MUTE)
CRYSTAL
STOP
8
26
MIX 1 IN
9
25
AGC RATE 2
MIX 1 OUT A
10
24
MIX 2 OUTA
MIX 1 OUTB
11
23
MIX 2 E B
22
MIX 2 E B
21
MIX 2
BYPASS
WB AGC 1 IN 12
RESET
WB
AGC
13
MIX 2 IN
19
WB AGC 2 IN
20
17
18
LOW-LEVEL
GROUND
OSC COIL
OSC BUFFER
15
REFERENCE
16
14
WB AGC OUT
V REF
Dwg. PS-012-1
Dwg. No. PS-012-1
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 determined 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-dependent 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.
ABSOLUTE MAXIMUM RATINGS
Supply Voltage, VCC . . . . . . . . . . . . . . 12 V
Package Power Dissipation, PD . . . . 1.2 W
Operating Temperature Range,
TA . . . . . . . . . . . . . . . -40°C to +105°C
Storage Temperature Range,
TS . . . . . . . . . . . . . . . -65°C to +150°C
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
■ Low Noise Figure
■ Field-Strength Indicator
■ Balanced Mixers
■ Buffered Oscillator
■ High Dynamic Range First Mixer ■ Fast Scan Mode
Always order by complete part number: A3848EEQ .
3848
DUAL-CONVERSION AM RECEIVER
ELECTRICAL CHARACTERISTICS at TA = +25°C, VCC = 10 V, fo = 1 MHz, fif1 = 10.7 MHz,
fif2 = 450 kHz, Vin = 10 mV; fm = 1 kHz , Mod = 30% (except as noted).
Characteristic
Symbol
Supply Current
ICC
Test Conditions
Limits
Max
Min
Typ
Units
I2, Vin = 0
—
50
65
mA
I2, Vin = 0, V27 = 0 (Muted)
—
1.0
6.0
mA
Sensitivity
Vin
Vout = 50 mV
—
6.0
10
µV
Usable Sensitivity
Vin
S + N/N = 20 dB
—
14
21
µV
Recovered Audio
Vout
165
215
265
mV
Total Harmonic Dist.
THD
Mod = 90%
—
0.4
2.0
%
V17
80
120
—
mV
V8, Vin = 0
4.7
5.0
—
V
V8, Mod = 0%
—
0.10
0.16
V
V12 = 2.5 V, Mod = 0%
30
45
60
µV
V8 = 2.5 V, = 0%
5.0
6.5
8.0
kHz
Vin = 0
5.0
6.7
8.0
V
Vin = 11 mV, Mod = 0%
3.7
5.0
—
V
Vin = 26 mV, Mod = 0%
—
—
1.0
V
Vin = 0
—
0.1
0.4
V
Vin = 30 µV, Mod = 0%
0.25
0.60
1.05
V
Vin = 100 µV, Mod = 0%
1.1
1.6
2.2
V
Vin = 1 mV, Mod = 0%
1.8
2.5
3.2
V
Vin = 10 mV, Mod = 0%
3.1
3.7
4.4
V
Vin = 0
—
—
0.5
V
Vin = 30 µV, Mod = 0%
0.9
1.1
1.5
V
Vin = 100 µV, Mod 0%
1.3
1.6
2.0
V
Vin = 1 mV, Mod = 0%
2.3
2.9
3.5
V
Vin = 10 mV, Mod = 0%
2.5
3.7
4.0
V
Vout = 3% THD, Mod = 90%
60
100
—
mV
First Mixer (Note 2)
350
450
—
mV
—
12
—
µV
200
250
320
mV
Oscillator Output
Stop Output Voltage
Vo
VSTP
Stop Sensitivity
Vstp
Stop Bandwidth
BWSTP
Wide-Band AGC
VAGC
Field-Strength
Indicator
Output Voltage
(unmodulated,
AGC Reset Low)
Field-Strength
Indicator
Output Voltage
(unmodulated,
AGC Reset High)
Overload
VFSI
VFSI
Vin
-3dB Limiting
Vin
Mod = 3 kHz peak deviation
IF Output Voltage
Vout
Vin = 1 mV
FM Recovered Audio
Vout
V7, Mod = 3 kHz peak deviation
—
380
—
mV
Signal to Noise Ratio
S+N/N
Vin = 1 mV
50
53
—
dB
Vin = 10 mV
53
56
—
dB
Ref. at Vin = 10 mV, Vin for Vout = -10 dB
7.0
10
14
µV
AGC Figure of Merit
FOM
Continued next page...
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
W
Copyright © 1993, Allegro MicroSystems, Inc.
3848
DUAL-CONVERSION AM RECEIVER
ELECTRICAL CHARACTERISTICS at TA = +25°C, VCC = 10 V, fo = 1 MHz, fif1 = 10.7 MHz,
fif2 = 450 kHz, Vin = 10mV; fm = 1 kHz, Mod = 30% (except as noted) (concluded)
Characteristic
Regulator Voltage
Reference Voltage
Symbol
VREG
VREF
Test Conditions
Min
Typ
Limits
Max
V6
4.7
5.0
5.3
V
V6, V27 = 0 (Muted)
—
0
0.3
V
V15
3.2
3.4
3.6
V
Units
NOTES: 1. Typical data is for design information only.
2. Attenuate MIXER 1 output with 50 Ω load on mixer coil secondary, Vout =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 responsibility 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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