3848
DUAL-CONVERSION AM RECEIVER
3848
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.
Data Sheet
27121.15
DUAL-CONVERSION AM RECEIVER
HIGH-LEVEL
GROUND
AUDIO OUT
REGULATOR
AFC OUT
STOP
MIX 1 IN
MIX 1 OUT
A
MIX 1 OUT
B
WB AGC 1 IN
12
RESET
ABSOLUTE MAXIMUM RATINGS
Supply Voltage, V
CC
. . . . . . . . . . . . . .
12 V
Package Power Dissipation, P
D
. . . .
1.2 W
Operating Temperature Range,
T
A
. . . . . . . . . . . . . . .
-40
擄
C to +105
擄
C
Storage Temperature Range,
T
S
. . . . . . . . . . . . . . .
-65
擄
C to +150
擄
C
T
C
U Y
D L
O N
R O
P E
D C
E N
U E
N R
I E
T F
N E
O R
C R
S
I O
D F
鈥?/div>
SUPPLY
31
IF BIAS
IF OUT
V
CC
SUB
32
30
4
2
3
1
DECOUPLE
DETECTOR
FSI
5
6
7
8
9
29
28
27
MIX 2 OUT
B
IF
V
REG
DET
AGC (MUTE)
26
25
24
CRYSTAL
AGC RATE 2
MIX 2 OUT
A
MIX 2 E
B
10
11
23
WB
AGC
22
MIX 2 E
B
13
21
MIX 2
BYPASS
V
REF
14
15
17
18
19
16
REFERENCE
LOW-LEVEL
GROUND
OSC BUFFER
WB AGC OUT
WB AGC 2 IN
OSC COIL
MIX 2 IN
20
Dwg. PS-012-1
Dwg. No. PS-012-1
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擄C to +105擄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
.
1
2
3
4
