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.