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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 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. 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.
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 OUTB
WB AGC 1 IN 12 RESET
ABSOLUTE MAXIMUM RATINGS
Supply Voltage, VCC . . . . . . . . . . . . . . 12 V Package Power Dissipation, PD . . . . 1.2 W Operating Temperature Range, TA . . . . . . . . . . . . . . . -40C to +105C Storage Temperature Range, TS . . . . . . . . . . . . . . . -65C to +150C
T C UY DL ON RO PE DC EN UE IN ER TF NE OR CR IS O DF --
SUPPLY 31 IF BIAS IF OUT
VCC
SUB
32
30
4
2
3
1
DECOUPLE
DETECTOR
FSI
5 6 7 8 9
29 28 27
MIX 2 OUTB IF
V REG
DET
AGC (MUTE)
26 25 24
CRYSTAL
AGC RATE 2 MIX 2 OUTA 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-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. 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 -40C to +105C 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 .
3848
DUAL-CONVERSION AM RECEIVER
ELECTRICAL CHARACTERISTICS at TA = +25C, 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 Supply Current Symbol ICC Vin Vin Vout THD Vo VSTP Vstp BWSTP VAGC Mod = 90% V17 V8, Vin = 0 V8, Mod = 0% Stop Sensitivity Stop Bandwidth Wide-Band AGC V12 = 2.5 V, Mod = 0% V8 = 2.5 V, = 0% Vin = 0 Vin = 11 mV, Mod = 0% Vin = 26 mV, Mod = 0% Field-Strength Indicator Output Voltage (unmodulated, AGC Reset Low) VFSI Vin = 0 Vin = 30 V, Mod = 0% Vin = 100 V, Mod = 0% Vin = 1 mV, Mod = 0% Vin = 10 mV, Mod = 0% Field-Strength Indicator Output Voltage (unmodulated, AGC Reset High) VFSI Vin = 0 Vin = 30 V, Mod = 0% Vin = 100 V, Mod 0% Vin = 1 mV, Mod = 0% Vin = 10 mV, Mod = 0% Overload Vin Vin Vout Vout S+N/N Vout = 3% THD, Mod = 90% First Mixer (Note 2) -3dB Limiting IF Output Voltage FM Recovered Audio Signal to Noise Ratio Mod = 3 kHz peak deviation Vin = 1 mV V7, Mod = 3 kHz peak deviation Vin = 1 mV Vin = 10 mV AGC Figure of Merit FOM Ref. at Vin = 10 mV, Vin for Vout = -10 dB Test Conditions I2, Vin = 0 I2, Vin = 0, V27 = 0 (Muted) Sensitivity Usable Sensitivity Recovered Audio Total Harmonic Dist. Oscillator Output Stop Output Voltage Vout = 50 mV S + N/N = 20 dB Min -- -- -- -- 165 -- 80 4.7 -- 30 5.0 5.0 3.7 -- -- 0.25 1.1 1.8 3.1 -- 0.9 1.3 2.3 2.5 60 350 -- 200 -- 50 53 7.0 Typ 50 1.0 6.0 14 215 0.4 120 5.0 0.10 45 6.5 6.7 5.0 -- 0.1 0.60 1.6 2.5 3.7 -- 1.1 1.6 2.9 3.7 100 450 12 250 380 53 56 10 Limits Max 65 6.0 10 21 265 2.0 -- -- 0.16 60 8.0 8.0 -- 1.0 0.4 1.05 2.2 3.2 4.4 0.5 1.5 2.0 3.5 4.0 -- -- -- 320 -- -- -- 14 Units mA mA V V mV % mV V V V kHz V V V V V V V V V V V V V mV mV V mV mV dB dB V
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115 Northeast Cutoff, Box 15036 W Worcester, Massachusetts 01615-0036 (508) 853-5000 Copyright (c) 1993, Allegro MicroSystems, Inc.
3848
DUAL-CONVERSION AM RECEIVER
ELECTRICAL CHARACTERISTICS at TA = +25C, 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 Symbol VREG VREF Test Conditions V6 V6, V27 = 0 (Muted) Reference Voltage V15 Min 4.7 -- 3.2 Typ 5.0 0 3.4 Limits Max 5.3 0.3 3.6 Units V V V
NOTES: 1. Typical data is for design information only. 2. Attenuate MIXER 1 output with 50 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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