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Low Distortion AGC Compression Amplifier
LP502 CUSTOM DATA SHEET
FEATURES • adjustable gain from 0 to 60 dB • 0.94 V DC voltage regulator on-chip • attack time fixed at less than 1 ms • release time adjustable from 40 to 500 ms • low input referred noise 1.2 µV • <1 % distortion at 10 mVRMS output • operates from 1.05 to 3 VDC STANDARD PACKAGING • 8 pin MICROpac • 8 pin PLID ® • Chip (64 x 62 mils) Au Bump Internally, a series shunt voltage regulator produces a 0.94 V DC regulated output voltage. This provides a bias for electret microphones and permits circuit operations over a wide range of supply voltages, 1.05 to 3 VDC for LP502 without any degradation of electrical performances. As compared to the LD502, the LP502 incorporates an additional diode between the amplifier output and the AGC filter point. This “attack diode” is responsible for precharging the AGC filter point, which enables quicker attack time and helps to reduce the gain overshoot (during transients) that is observed in the LD502 with certain combinations of AGC input coupling and filter capacitors. However, with this diode connected, some level of AGC is always present with higher output levels even when the AGC input is disconnected. Therefore the LP502 cannot be used as a “pure” linear amplifier.
GAIN SET 7 4
By using RGT (see test circuit) to vary the value of this current controlled resistance, the amplifier gain and compression threshold can be controlled over a range of 60 dB. The AGC current is derived from a full wave rectifier driven by a differential amplifier. The attack time of the AGC circuit is fixed at less than 1 ms. The release time is adjustable from 40 to 500 ms by selecting the value of an external capacitor (C3).
DESCRIPTION The LP502 is a compression (AGC) preamplifier that consists of a single-ended input inverting amplifier, with an internal current controlled resistance connected between input and output.
VB
2 VREG
VOLTAGE REGULATOR
1 A IN
AMPLIFIER
A OUT 3
FULL WAVE RECTIFIER
AGC IN 6
8 GND
5 AGC FILTER
BLOCK DIAGRAM
Patented 1985 Canada 1183580 Patent Pending Europe 83.300836.0 USA 4506169 Japan 58-06886
Document No. HP2802-1
GENNUM CORPORATION P.O. Box 489, Stn A, Burlington, Ontario, Canada L7R 3Y3
tel. (905) 632-2996 fax: (905) 632-5946
Gennum Japan Corporation:C-101 Mi yamae Vill age, 2–10–42 Mi yamae, Suginami–ku, Tokyo 168-0081, Japan tel. (03) 3334-7700 fax (03) 3247-8839
ABSOLUTE MAXIMUM RATINGS
PARAMETER Supply Voltage Power Dissipation Operating Temperature Range Storage Temperature Range VALUE/UNITS 3 V DC 25 mW -10°C to 50° C -20°C to 70° C GAIN SET A OUT VREG A IN
PIN CONNECTION
4
5
AGC FILTER AGC IN VB
1
8
GND
CAUTION CLASS 1 ESD SENSITIVITY
ELECTRICAL CHARACTERISTICS
Conditions: Frequency = 1 kHz, Temperature = 25°C, Supply Voltage V B = 1.3 VDC
PARAMETER Gain
SYMBOL AV
CONDITIONS VOUT = 11.0 mV, 20 Log ( V OUT V IN )
MIN 38
TYP 41
MAX 46
UNITS dB
Output Level Distortion -Linear - AG.