TL441AM
LOGARITHMIC AMPLIFIER
SLFS038 JUNE 1976 REVISED FEBRUARY 1989
1
POST OFFICE BOX 655303
·
DALLAS, TEXAS 75265
D
Excellent Dynamic Range
D
Wide Bandwidth
D
Built-In Temperature Compensation
D
Log Linearity (30 dB Sections) . . . 1 dB Typ
D
Wide Input Voltage Range
description
This monolithic amplifier circuit contains four
30-dB logarithmic stages. Gain in each stage is
such that the output of each stage is proportional
to the logarithm of the input voltage over the 30-dB
input voltage range. Each half of the circuit
contains two of these 30-dB stages summed
together in one differential output that is
proportional to the sum of the logarithms of the
input voltages of the two stages. The four stages
may be interconnected to obtain a theoretical
input voltage range of 120-dB. In practice, this
permits the input voltage range to be typically
greater than 80-dB with log linearity of
±
0.5-dB
(see application data). Bandwidth is from dc to
40 MHz.
This circuit is useful in military weapons systems,
broadband radar, and infrared reconnaissance
systems. It serves for data compression and
analog compensation. This logarithmic amplifier
is used in log IF circuitry as well as video and log
amplifiers. The TL441AM is characterized for
operation over the full military temperature range
of 55
°
C to 125
°
C.
Copyright
©
1989, Texas Instruments Incorporated
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
C
A2
V
CC
C
A2
A1
Y
Y
A2
V
CC +
NC
C
B2
C
B2
GND
B1
Z
Z
B2
J PACKAGE
(TOP VIEW)
3
2
1 20 19
9 10 11 12 13
4
5
6
7
8
18
17
16
15
14
C
B2
GND
NC
B1
Z
C
A2
A1
NC
Y
Y
FK PACKAGE
(TOP VIEW)
V
C
NC
B2
Z
NC
C
A2
V
NC
NC -- No internal connection
A2
B2
CC +
CC
15 dB
15 dB
Log
Log
Log
Log
Y (Z)
Y (Z)
A1
(B1)
CA2
(CB2)
CA2
(CB2
)
Y
log A1 + log A2; Z
log B1 + log B2
where: A1, A2, B1, and B2 are in dBV, 0 dBV = 1 V.
CA2, CA2
, CB2, and CB2
are detector compensation inputs.
A2
(B2)
functional block diagram (one half)
TL441AM
LOGARITHMIC AMPLIFIER
SLFS038 JUNE 1976 REVISED FEBRUARY 1989
2
POST OFFICE BOX 655303
·
DALLAS, TEXAS 75265
schematic
VCC +
Y
Y
A2
A1
CA2
CA2
VCC
8
6
5
7
4
3
1
2
10
11
9
12
13
14
15
Z
Z
B2
B1
GND
CB2
CB2
Pin numbers shown are for the J package.
absolute maximum ratings over operating free-air temperature range (unless otherwise noted)
Supply voltages (see Note 1): V
CC+
8
V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
V
CC
8
V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Input voltage (see Note 1)
6 V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Output sink current (any one output)
30 mA
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Continuous total dissipation
See Dissipation Rating Table
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operating free-air temperature range
55
°
C to 125
°
C
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Storage temperature range
65
°
C to 150
°
C
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Case temperature for 60 seconds: FK package
260
°
C
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lead temperature 1,6 mm (1/16 inch) from case for 60 seconds: J package
300
°
C
. . . . . . . . . . . . . . . . . . . . .
Stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. This is a stress rating only, and
functional operation of the device at these or any other conditions beyond those indicated in the recommended operating conditions section of this
specification is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
NOTE 1: All voltages, except differential output voltages, are with respect to network ground terminal.
DISSIPATION RATING TABLE
PACKAGE
TA
25
°
C
POWER RATING
DERATING
FACTOR
DERATE
ABOVE TA
TA = 70
°
C
POWER RATING
TA = 125
°
C
POWER RATING
FK
500 mW
11.0 mW/
°
C
104
°
C
500 mW
275 mW
J
500 mW
11.0 mW/
°
C
104
°
C
500 mW
275 mW
recommended operating conditions
MIN
MAX
UNIT
Peak-to-peak input voltage for each 30-dB stage
0.01
1
V
Operating free-air temperature, TA
55
125
°
C
TL441AM
LOGARITHMIC AMPLIFIER
SLFS038 JUNE 1976 REVISED FEBRUARY 1989
3
POST OFFICE BOX 655303
·
DALLAS, TEXAS 75265
electrical characteristics, V
CC
±
=
±
6 V, T
A
= 25
°
C
PARAMETER
TEST
FIGURE
MIN
TYP
MAX
UNIT
Differential output offset voltage
1
±
25
±
70
mV
Quiescent output voltage
2
5.45
5.6
5.85
V
DC scale factor (differential output), each 3-dB stage, 35 dBV to 5 dBV
3
7
8
11
mV/dB
AC scale factor (differential output)
8
mV/dB
DC error at 20 dBV (midpoint of 35 dBV to 5 dBV range)
3
1
2.6
dB
Input impedance
500
Output impedance
200
Rise time, 10% to 90% points, CL = 24 pF
4
20
35
ns
Supply current from VCC+
2
14.5
18.5
23
mA
Supply current from VCC
2
6
8.5
10.5
mA
Power dissipation
2
123
162
201
mW
electrical characteristics over operating free-air temperature range, V
CC
±
=
±
6 V (unless otherwise
noted)
PARAMETER
TEST
FIGURE
MIN
MAX
UNIT
Differential output offset voltage
1
±
100
mV
Quiescent output voltage
2
5.3
5.85
V
DC scale factor (differential output) each 30-dB stage, 35 dBV to 5 dBV
3
7
11
mV/dB
DC error at
20 dBV (midpoint of
35 dBV to
5 dBV range)
TA = 55
°
C
3
4
dB
DC error at 20 dBV (midpoint of 35 dBV to 5 dBV range)
TA = 125
°
C
3
3
dB
Supply current from VCC+
2
10
31
mA
Supply current from VCC
2
4.5
15
mA
Power dissipation
2
87
276
mW
PARAMETER MEASUREMENT INFORMATION
Figure 1
VCC+
VCC
CA2 CA2
VCC + VCC
Y
Y
Z
Z
DVM
CB2 CB2
GND
A1
A2
B1
B2
Figure 2
CA2 CA2
VCC+ VCC
Y
Y
Z
Z
CB2 CB2
GND
A1
A2
B1
B2
VCC+
VCC
ICC +
ICC
VO
PD = VCC+
·
ICC+ + VCC
·
ICC
TL441AM
LOGARITHMIC AMPLIFIER
SLFS038 JUNE 1976 REVISED FEBRUARY 1989
4
POST OFFICE BOX 655303
·
DALLAS, TEXAS 75265
PARAMETER MEASUREMENT INFORMATION
CA2 CA2
VCC+ VCC
Y
Y
Z
Z
CB2
GND
A1
A2
B1
B2
DVM
18 mV
100 mV
560 mV
DC
Power
Supply
VCC+ VCC
Scale Factor
+
V
out(560 mV)
V
out(18mV)
mV
30 dB
Error
+
VV
out(100 mV)
0.5 V
out(560 mV)
0.5 V
out(18 mV)
Scale Factor
CB2
Figure 3
CA2 CA2
VCC+ VCC
Y
Y
Z
Z
CB2 CB2
GND
A1
A2
B1
B2
VCC+
VCC
1000 pF
CI
CL
CL
100 mV
0 mV
Atten
Pulse
Generator
50
Tektronix
Sampling Scope
With Digital
Readout or
Equivalent
NOTES: A. The input pulse has the following characteristics: tw = 200 ns, tr
2 ns, tf
2 ns, PRR
10 MHz.
B. Capacitor CI consists of three capacitors in parallel: 1
µ
F, 0.1
µ
F, and 0.01
µ
F.
C. CL includes probe and jig capacitance.
Figure 4
TL441AM
LOGARITHMIC AMPLIFIER
SLFS038 JUNE 1976 REVISED FEBRUARY 1989
5
POST OFFICE BOX 655303
·
DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
Figure 5
DIFFERENTIAL OUTPUT OFFSET VOLTAGE
vs
FREE-AIR TEMPERATURE
TA Free-Air Temperature
°
C
60
50
40
30
20
10
0
75 50 25
0
25
50
75
100
125
Differential Output Offset V
oltage mV
VCC
±
=
±
6 V
See Figure 1
Figure 6
QUIESCENT OUTPUT VOLTAGE
vs
FREE-AIR TEMPERATURE
TA Free-Air Temperature
°
C
75 50 25
0
25
50
75
100
125
8
7
6
5
4
3
2
1
0
Quiescent Output V
oltage V
VCC
±
=
±
6 V
See Figure 2
Figure 7
TA Free-Air Temperature
°
C
75 50 25
0
25
50
75
100
125
12
10
8
6
4
2
0
DC SCALE FACTOR
vs
FREE-AIR TEMPERATURE
DC Scale Factor (Differential Output) mV/dBV
VCC
±
=
±
6 V
See Figure 3
Figure 8
TA Free-Air Temperature
°
C
75 50 25
0
25
50
75
100
125
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
DC ERROR
vs
FREE-AIR TEMPERATURE
DC Error at Midpoint of 30-dBV Range dBV
VCC
±
=
±
6 V
See Figure 3
TL441AM
LOGARITHMIC AMPLIFIER
SLFS038 JUNE 1976 REVISED FEBRUARY 1989
6
POST OFFICE BOX 655303
·
DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
t
r
0
5
10
15
20
25
30
0
5
10
15
20
25
VCC
±
=
±
6 V
TA = 25
°
C
See Figure 4, outputs
loaded symmetrically
CL Load Capacitance pF
OUTPUT RISE TIME
vs
LOAD CAPACITANCE
Output Rise T
ime ns
Figure 9
TA Free-Air Temperature
°
C
75 50 25
0
25
50
75
100
125
VCC
±
=
±
6 V
See Figure 3
Power Dissipation mW
200
180
160
140
120
100
80
60
40
20
0
POWER DISSIPATION
vs
FREE-AIR TEMPERATURE
Figure 10
TL441AM
LOGARITHMIC AMPLIFIER
SLFS038 JUNE 1976 REVISED FEBRUARY 1989
7
POST OFFICE BOX 655303
·
DALLAS, TEXAS 75265
APPLICATION INFORMATION
Although designed for high-performance applications such as broadband radar, infrared detection and
weapons systems, this device has a wide range of applications in data compression and analog computation.
basic logarithmic function
The basic logarithmic response is derived from
the exponential current-voltage relationship of
collector current and base-emitter voltage. This
relationship is given in the equation:
m
·
V
BE
= In [(I
C
+ I
CES
)/I
CES
]
where:
I
C
=
collector current
I
CES
=
collector current at V
BE
= 0
m =
q/kT (in V
1
)
V
BE
=
base-emitter voltage
The differential input amplifier allows dual-polarity
inputs, is self-compensating for temperature
variations, and is relatively insensitive to
common-mode noise.
logarithmic sections
As can be seen from the schematic, there are eight differential pairs. Each pair is a 15-dB log subsection, and
each input feeds two pairs for a range of 30-dB per stage.
Four compensation points are made available to allow slight variations in the gain (slope) of the two individual
15-dB stages of input A2 and B2. By slightly changing the voltage on any of the compensation pins from its
quiescent value, the gain of that particular 15-dB stage can be adjusted to match the other 15-dB stage in the
pair. The compensation pins may also be used to match the transfer characteristics of input A2 to A1 or B2 to
B1.
The log stages in each half of the circuit are summed by directly connecting their collectors together and
summing through a common-base output stage. The two sets of output collectors are used to give two log
outputs, Y and Y (or Z and Z) which are equal in amplitude but opposite in polarity. This increases the versatility
of the device.
By proper choice of external connections, linear amplification, and linear attenuation, and many different
applications requiring logarithmic signal processing are possible
input levels
The recommended input voltage range of any one stage is given as 0.01 V to 1 V. Input levels in excess of
1 V may result in a distorted output. When several log sections are summed together, the distorted area of one
section overlaps with the next section and the resulting distortion is insignificant. However, there is a limit to the
amount of overdrive that may be applied. As the input drive reaches
±
3.5 V, saturation occurs, clamping the
collector-summing line and severely distorting the output. Therefore, the signal to any input must be limited to
approximately
±
3 V to ensure a clean output.
Figure 11
INPUT
A1
CA2
INPUT
A2
CA2'
Log
Log
Log
Log
Log
Log
Log
Log
15 dB
15 dB
15 dB
15 dB
Y
Y
Z
Z
Outputs
INPUT
B1
CB2
INPUT
B2
CB2'
functional block diagram
TL441AM
LOGARITHMIC AMPLIFIER
SLFS038 JUNE 1976 REVISED FEBRUARY 1989
8
POST OFFICE BOX 655303
·
DALLAS, TEXAS 75265
APPLICATION INFORMATION
output levels
Differential-output-voltage levels are low, generally less than 0.6 V. As demonstrated in Figure 12, the output
swing and the slope of the output response can be adjusted by varying the gain by means of the slope control.
The coordinate origin may also be adjusted by positioning the offset of the output buffer.
circuits
Figures 12 through 19 show typical circuits using this logarithmic amplifier. Operational amplifiers not otherwise
designated are TLC271. For operation at higher frequencies, the TL592 is recommended instead of the
TLC271.
Output V
oltage V
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0.2
10 4
10 3
10 2
10 1
101
1
TYPICAL TRANSFER
CHARACTERISTICS
Adjusted for Increased
Slope and Offset
Adjusted For Minimum
Slope With Zero Offset
Input Voltage V
Input
A1
A2
Y
Y
1/2
TL441
Origin
Slope
Output
GND
+
+
Figure 12. Output Slope and Origin Adjustment
TL441AM
LOGARITHMIC AMPLIFIER
SLFS038 JUNE 1976 REVISED FEBRUARY 1989
9
POST OFFICE BOX 655303
·
DALLAS, TEXAS 75265
APPLICATION INFORMATION
Output V
oltage V
Input Voltage V
Input
B1
B2
1/2
TL441
Output
Z
Z
2 k
, 1%
2 k
, 1%
2 k
, 1%
2 k
, 1%
GND
0.4
0.3
0.2
0.1
0
0.001
0.01
0.1
1
10
TRANSFER CHARACTERISTICS
OF TWO TYPICAL INPUT STAGES
20 k
+
Figure 13. Utilization of Separate Stages
TL441AM
LOGARITHMIC AMPLIFIER
SLFS038 JUNE 1976 REVISED FEBRUARY 1989
10
POST OFFICE BOX 655303
·
DALLAS, TEXAS 75265
APPLICATION INFORMATION
Z
Z
A1
A2
Y
Y
B1
B2
TL441
Input
Output
2 k
, 1%
2 k
, 1%
20 k
2 k
, 1%
2 k
, 1%
Output V
oltage V
Input Voltage V
0.4
0.3
0.2
0.1
0
0.001
0.01
0.1
1
10
TRANSFER CHARACTERISTICS
WITH BOTH SIDES PARALLELED
GND
+
Figure 14. Utilization of Paralleled Inputs
TL441AM
LOGARITHMIC AMPLIFIER
SLFS038 JUNE 1976 REVISED FEBRUARY 1989
11
POST OFFICE BOX 655303
·
DALLAS, TEXAS 75265
APPLICATION INFORMATION
Output V
oltage V
10 4
10 3
10 2
10 1
101
1
Input Voltage V
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
TRANSFER CHARACTERISTICS
1 k
910
VCC + = 4 V
VCC = 4 V
5 k
1 k
910
100
15 k
2 k
2 k
20 k
2 k
Slope
5 k
Input
Output
Z
Z
A1
A2
Y
Y
B1
B2
TL441
5 k
Origin
100
+
+
+
VCC + = 4 V
VCC = 4 V
NOTES: A. Inputs are limited by reducing the supply voltages for the input amplifiers to
±
4 V.
B. The gains of the input amplifiers are adjusted to achieve smooth transitions.
Figure 15. Logarithmic Amplifier With Input Voltage Range Greater Than 80 dB
TL441AM
LOGARITHMIC AMPLIFIER
SLFS038 JUNE 1976 REVISED FEBRUARY 1989
12
POST OFFICE BOX 655303
·
DALLAS, TEXAS 75265
APPLICATION INFORMATION
Z
Z
A1
A2
Y
Y
B1
B2
TL441
A1
A2
Y
Y
1/2
TL441
Input
A
Input
B
see
Note A
OUTPUT W
(see Note B)
R
R
R
R
R
R
R
R
R
R
+
+
+
+
+
NOTES: A. Connections shown are for multiplication. For division, Z and Z connections are reversed.
B. Output W may need to be amplified to give actual product or quotient of A and B.
C. R designates resistors of equal value, typically 2 k
to 10 k
.
Multiplication: W = A
·
B
log W = log A + log B, or W = a(logaA + logaB)
Division: W = A/B
log W = log A log B, or W = a(logaA + logaB)
Figure 16. Multiplication or Division
Input
A
A1
A2
Y
Y
1/2
TL441
Z
Z
B1
B2
Output
W
1/2
TL441
R
R
R
nR
R
nR
R
R
+
+
+
+
NOTE: R designates resistors of equal value, typically 2 k
to 10 k
. The power to which the input variable is raised is fixed by setting nR.
Output W may need to be amplified to give the correct value.
Exponential: W = An
log W = n log A, or W = a(n loga A)
Figure 17. Raising a Variable to a Fixed Power
TL441AM
LOGARITHMIC AMPLIFIER
SLFS038 JUNE 1976 REVISED FEBRUARY 1989
13
POST OFFICE BOX 655303
·
DALLAS, TEXAS 75265
APPLICATION INFORMATION
2 k
2 k
Origin
20 k
2 k
2 k
Slope
A1
A2
Y
Y
1/2
TL441
Input
A
Output
W
+
+
NOTE: Adjust the slope to correspond to the base "a".
Exponential to any base: W = a.
Figure 18. Raising a Fixed Number to a Variable Power
+
20 k
20 k
Input
1
2.2 k
0.2
µ
F
Output
1
Input
2
Output
2
TL592
TL592
0.2
µ
F
1 k
1 k
Gain Adj.
2.2 k
2.2 k
2.2 k
0.2
µ
F
0.2
µ
F
1 k
1 k
0.2
µ
F
Gain Adj. = 400
For 30 dB
Gain Adj. = 400
For 30 dB
0.2
µ
F
TL592
TL592
50
50
50
Open
Open
CA2 CA2'
Y
Y
Z
Z
CB2 CB2'
A1
A2
B1
B2
TL441
10
k
10
k
VCC
Gain Adj.
+
+
+
50
+
+
Figure 19. Dual-Channel RF Logarithmic Amplifier With 50-dB Input Range Per Channel at 10 MHz
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accordance with TI's standard warranty. Testing and other quality control techniques are utilized to the extent
TI deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily
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Copyright
©
1998, Texas Instruments Incorporated
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