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 OUTB
WB AGC OUT
OSC COIL
OSC BUFFER
LOW-LEVEL
GROUND
WB AGC 2 IN
MIX 2 IN
Dwg. PS-012-1
V
REF
REFERENCE
1234
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
303132
11
22
23
WB AGC 1 IN
MIX 2 E
B
21RESET
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
n Low Noise Figure n Field-Strength Indicator
n Balanced Mixers n Buffered Oscillator
n High Dynamic Range First Mixer n 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