Class A Amplifier with 3
Independent Gain Blocks
LC508 DATA SHEET
FEATURES
•
1
µ
V input referred noise
•
1.0 to 5 VDC operating range
•
73 dB typical gain (adjustable)
•
0.28 to 2.0 mA range of transducer current
•
1% electrical distortion
•
the first and second blocks, or second and third
blocks can be DC coupled
•
100 Hz to 50 kHz frequency response
•
suitable for active filtering
STANDARD PACKAGING
• 10 PIN MICROpac
•10 pin PLID
®
• 10 pin SLT
• Chip (52 x 49 mils)
DESCRIPTION
The LC508 is a 10 pin Class A amplifier utilizing Gennum's
proprietary low voltage bipolar JFET technology. It consists of
3 single ended, low noise inverting gain blocks. The first two
blocks have a typical open loop gain of 50 dB. The closed loop
gain is set by the ratio of the feedback resistor to the source
impedance. The third block is an open collector output stage
with the bias being set by
R
E
and
V
RE
at pin 8 which is 54 mV.
Typically, the gain of the first two blocks is set to 25 dB each,
with the third block at 23 dB, giving a total gain of 73 dB.
Gain trim can be accomplished with the use of a feedback
resistor on the first block, while the volume control is used as
the feedback control on the second block. This gives a volume
control range greater than 40 dB.
V
B
6
5
MIC
R
MIC
V
A IN
4
7
- A
- B
- C
8
R
E
C OUT
R
E
2
A OUT
3
B IN
10
B OUT
9
C IN
1
GND
BLOCK DIAGRAM
Revision Date: January 2001
Document No. 500 - 61 - 12
GENNUM CORPORATION P.O. Box 489, Stn. A, Burlington, Ontario, Canada L7R 3Y3 tel. +1 (905) 632-2996
Web Site: www.gennum.com E-mail: hipinfo@gennum.com
ABSOLUTE MAXIMUM RATINGS
PARAMETER
Supply Voltage
Power Dissipation
Operating Temperature
Storage Temperature
o
o
PIN CONNECTION
VALUE / UNITS
5V DC
25 mW
-10 to + 40 C
-20 to + 70 C
o
o
V
MIC
A IN
B IN
A OUT
5
6
V
B
C OUT
R
E
C IN
1
10
B OUT
CAUTION
CLASS 1 ESD SENSITIVITY
GND
ELECTRICAL CHARACTERISTICS
Conditions: Supply Voltage =1.3 VDC, Frequency = 1 kHz, Temperature = 25
o
C
PARAMETER
Gain (Closed Loop)
Amplifier Current
Transducer Current
Transducer Current
Distortion
Input Referred Noise
Stable with Battery Resistance to
Input Bias Current
On Chip Emitter Resistor
Emitter Bias Voltage (pin 8)
Microphone Decoupling Resistor
SYMBOL
A
CL
I
AMP
I
TRANS H
I
TRANS L
THD
IRN
R
B
I
B
R
E
V
RE
R
MIC
CONDITIONS
V
OUT
= 500 V
RMS
I
AMP
=
I
A
+
I
MIC
R
E
= 47.5
R
E
=
∞
V
OUT
= 500 V
RMS
NFB 0.2 to 10kHz at 12dB/Oct
MIN
69
160
1.1
200
-
-
-
-50
-
-
-
TYP
73
245
1.3
275
1
1
-
0
200
54
4
MAX
77
340
1.7
350
4
2
22
50
-
-
-
UNITS
dB
µA
mA
µA
%
µV
Ω
nA
Ω
mV
kΩ
All switches and parameters remain as shown in Test Circuit unless otherwise stated in Conditions column.
I
AMP
VB=1.3 VDC
R B =4.7
6
I
MIC
5
R
MIC
V
OUT
R
L
= 1K
3.3 K
33 K
1.0
8
10
I
B
V
IN
4
- A
- B
- C
7
I
TRA NS
RE
C
S
0.015
1kHz
R
FA
56.2K
2
R1
3
C
S
I
B
R
FB
47.5K
10
9
1
2.7K 1.0
1.0
R E =47.5
All resistors in ohms, all capacitors in
µF
unless otherwise stated
Fig. 1 Test Circuit
500 - 61 - 12
2
5
R
MIC
6
7
2
10
33K
8
4
3
9
R
E
1
All external resistors in ohms, all capacitors in
µF
unless otherwise stated
Fig. 2 Functional Schematic
V
B
=1.3 VDC
6
5
10
R
S
≈
3.9k
C
S
0.22
R
E
0.015
4
7
R
MIC
R
L
= 1K
- A
- B
- C
2
50K
2.7K
R1
R
GT
3
50K
10
9
1
8
47
0.033
R
VC
All resistors in ohms, all capacitors in
µF
unless otherwise stated
Gain of Stage A = 20 Log
10
(
R
GT
R
S
)
Gain of Stage B = 20 Log
10
(
R
VC
R
1
)
Gain of Stage C = 20 Log
10
(
R
L
R
E
//47
)
Fig. 3 Typical Hearing Aid Application
3
500 - 61 - 12
10
0
R
-10
-20
R
= 47k
VC
VC
4
2
= 100k
0
C = 0.22µF
S
C = 0.1µF
S
C = 0.047µF
S
RELATIVE OUTPUT (dB)
-2
-4
-6
-8
-10
-12
-14
-16
-18
-20
20
OUTPUT (dBV)
-30
-40
-50
-60
-70
-80
-90
-140
R
= 22k
VC
R
= 10k
VC
R
= 3.3k
VC
C = 0.033µF
S
-120
-100
-80
-60
-40
-20
200
2K
20K
INPUT (dBV)
FREQUENCY (Hz)
Fig. 4
I/O
Characteristics at Various R
VC
Values
10
5
0
55
50
60
Fig. 5 Frequency Response at Various C
S
Values
RELATIVE GAIN (dB)
-5
-15
-20
-25
-30
-35
-40
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
GAIN (dB)
-10
45
40
35
30
25
20
10
100
1K
10K
100K
SUPPLY VOLTAGE (VDC)
FREQUENCY (Hz)
Fig.6 Gain vs Supply Voltage
60
Fig.7 Preamplifier A Open Loop
Frequency Response
RELATIVE TRANSDUCER CURRENT (µA)
60
50
40
30
20
10
0
-10
-20
-30
-40
-50
-60
-70
-80
-20
-10
0
10
20
O
RELATIVE AMPLIFIER CURRENT (µA)
50
40
30
20
10
0
-10
-20
-30
-40
-50
-60
-70
-80
-20
-10
0
10
20
O
30
40
50
30
40
50
TEMPERATURE ( C)
TEMPERATURE ( C)
Fig. 8 Amplifier Current vs Temperature
Fig. 9 Transducer Current vs Temperature
GENNUM CORPORATION
MAILING ADDRESS:
P.O. Box 489, Stn. A, Burlington, Ontario, Canada L7R 3Y3
Tel. +1 (905) 632-2996 Fax +1 (905) 632-2814
SHIPPING ADDRESS:
970 Fraser Drive, Burlington, Ontario, Canada L7L 5P5
DOCUMENT IDENTIFICATION:
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.
REVISION NOTES:
Changes to standard packaging information
GENNUM JAPAN CORPORATION
C-101, Miyamae Village, 2-10-42 Miyamae, Suginami-ku, Tokyo 168-0081,
Japan
Tel. +81 (3) 3334-7700 Fax: +81 (3) 3247-8839
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 March 1983 Gennum Corporation.
All rights reserved.
Printed in Canada.
500 - 61 - 12
4
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