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
µ
V
•
<1 % distortion at 10 mV
RMS
output
•
operates from 1.05 to 3 V
DC
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 V
DC
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 R
GT
(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.
V
B
2
V
REG
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
V
REG
A IN
PIN CONNECTION
4
5
AGC FILTER
AGC IN
V
B
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
A
V
CONDITIONS
V
OUT
= 11.0 mV,
20 Log (
V
OUT
V
IN
)
MIN
38
TYP
41
MAX
46
UNITS
dB
Output Level
Distortion -Linear
- AGC
Input Referred Noise
Compression Function Ratio
Total Amplifier Current
Regulated Voltage
Supply Rejection
V
OHIGH
THD
V
IN
= 6.32 mV, S1 closed
V
OUT
= 11.0 mV
V
IN
= 6.32mV, S1 closed
7.5
-
-
-
2
160
0.890
51
12
1
1
1.2
5
310
0.940
60
15.5
2.9
2.2
2.2
8
380
0.990
-
mV
%
%
µV
dB
µA
VDC
dB
IRN
S2 closed,NFB 0.2 to 10 kHz at 12 dB/Oct
V
IN
= 0.1 to 6.32 mV, S1 closed
I
AMP
V
REG
PSRR
All parameters and switches remain as shown in Test Circuit unless otherwise stated in "Conditions" column
I
TOT
R
GT
130k
V
B
= 1.3 VDC
7
4
2
VOLTAGE
REGULATOR
C5
1.0
R
TH
0Ω
V
OUT
C1
0.47
1
3
AMP
R
S
= 3.5k
FULL WAVE
RECTIFIER
6
S1
R
L
10K
S2
R
M
33K
C2
1.0
V
IN
C4
0.1
8
5
C3
1.0
All resistors in ohms, all capacitors in microfarads unless otherwise stated
Fig. 1 Test Circuit
HP2802-1
2
100
100
R
TH
=50kΩ
OUTPUT (mV)
R
TH
=22kΩ
R
TH
=10kΩ
10
R
TH
=0kΩ
10
OUTPUT (mV)
1
R
GT
=130kΩ
R
GT
=82kΩ
R
GT
=68kΩ
R
GT
=47kΩ
1
0.01
0.1
1.0
10
0.1
0.01
0.1
1.0
10
INPUT (mV)
INPUT (mV)
Fig. 4 I/O Characteristics at
Various R
TH
Values
Fig. 5 I/O Characteristics at
Various R
GT
Values
100
4
2
0
C
S
=0.22
µF
C
S
=0.1
µF
RELATIVE OUTPUT (dB)
R
TH
=0
-2
-4
-6
-8
-10
-12
-14
-16
-18
OUTPUT (mV)
V
B
=3 VDC
10
V
B
=1.3 VDC
C
S
=0.047
µF
C
S
=0.033
µF
0.1
0.01
0.1
1.0
10
-20
20
200
2K
20k
INPUT (mV)
FREQUENCY (Hz)
Fig. 6 Effects of Supply Voltage
Variation
Fig. 7 Frequency Response at
Various C
S
Values
4.0
3.0
THD (%)
2.0
DOCUMENT
IDENTIFICATION
PRODUCT PROPOSAL
This data has been compiled for market investigation purposes
only, and does not constitute an offer for sale.
ADVANCE INFORMATION NOTE
This product is in development phase and specifications are
subject to change without notice. Gennum reserves the right to
remove the product at any time. Listing the product does not
constitute an offer for sale.
PRELIMINARY DATA SHEET
The product is in a preproduction phase and specifications are
subject to change without notice.
DATA SHEET
The product is in production. Gennum reserves the right to make
changes at any time to improve reliability, function or design, in
order to provide the best product possible.
1.0
0.0
0.0
5.0
10.0
15.0
20.0
25.0
OUTPUT (mV)
Fig. 8 Total Harmonic Distortion
vs Output Level
Gennum Corporation assumes no responsibility for the use of any circuits described herein and makes no representations that they are free from patent infringement.
© Copyright August 1997 Gennum Corporation. All rights reserved. Printed in Canada.
HP2802-1
4
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