3848 ALLEGRO

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DUAL-CONVERSION AM RECEIVER DISCONTINUED PRODUCT — FOR REFERENCE ONLY MIX 2 EB 10 24 26STOP MIX 1 IN CRYSTAL AGC RATE 2 MIX 2 OUT DET WB AGC MIX 1 OUTA 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

4 IF OUT

AGC (MUTE) V REGREGULATOR 6 7 27 MIX 2 OUTFSI 5 29 B A WB AGC 1 IN MIX 2 EB 21RESET MIX 2 BYPASS 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 Mixern Fast Scan Mode Always order by complete part number: A3848EEQ . ABSOLUTE MAXIMUM RATINGS Operating Temperature Range, Storage Temperature Range, Data Sheet 27121.15

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 I2, Vin = 0 — 50 65 mA I2, Vin = 0, V27 = 0 (Muted) — 1.0 6.0 mA Sensitivity V in Vout = 50 mV — 6.0 10 µV Usable Sensitivity V in S + N/N = 20 dB — 14 21 µV Recovered Audio V out 165 215 265 mV Total Harmonic Dist. THD Mod = 90% — 0.4 2.0 % Oscillator Output V o V17 80 120 — mV Stop Output Voltage V STP V8, Vin = 0 4.7 5.0 — V V8, Mod = 0% — 0.10 0.16 V Stop Sensitivity V stp V12 = 2.5 V, Mod = 0% 30 45 60 µV Stop Bandwidth BW STP V8 = 2.5 V, = 0% 5.0 6.5 8.0 kHz Wide-Band AGC V AGC 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 VFSI 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 VFSI 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 Overload V in Vout = 3% THD, Mod = 90% 60 100 — mV First Mixer (Note 2) 350 450 — mV -3dB Limiting V in Mod = 3 kHz peak deviation — 12 — µV IF Output Voltage V out Vin = 1 mV 200 250 320 mV FM Recovered Audio V out V7, Mod = 3 kHz peak deviation — 380 — mV Signal to Noise Ratio S+N/N V in = 1 mV 50 53 — dB Vin = 10 mV 53 56 — dB AGC Figure of Merit FOM Ref. at V in = 10 mV, Vin for Vout = -10 dB 7.0 10 14 µV 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). 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.

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) Limits Characteristic Symbol Test Conditions Min Typ Max Units Regulator Voltage V REG V6 4.7 5.0 5.3 V V6, V27 = 0 (Muted) — 0 0.3 V Reference Voltage V REF V15 3.2 3.4 3.6 V 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 responsibil- ity for its use; nor for any infringements of patents or other rights of third parties which may result from its use.