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Intersil Electronic Components Datasheet

ICL8048 Datasheet

Log Amplifier

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ICL8048 pdf
Data Sheet
ICL8048
August 1999 File Number 2865.2
Log Amplifier
The ICL8048 is a monolithic logarithmic amplifier capable of
handling six decades of current input, or three decades of
voltage input. It is fully temperature compensated and is
nominally designed to provide 1V of output for each decade
change of input. For increased flexibility, the scale factor,
reference current and offset voltage are externally
adjustable.
Ordering Information
PART
ERROR TEMPERATURE
PKG.
NUMBER (25oC) RANGE (oC) PACKAGE NO.
ICL8048BCJE 30mV
0 to 70
16 Ld CERDIP F16.3
Pinout
ICL8048
(CERDIP)
TOP VIEW
GND 1
IIN 2
NC 3
A1 OFFSET
NULL
A1 OFFSET
NULL
V-
4
5
6
A1 OUTPUT 7
NC 8
16 IREF
15 GAIN
14 NC
13
A2 OFFSET
NULL
12 A2 OFFSET
NULL
11 V+
10 VOUT
9 NC
Features
• Full Scale Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . 0.5%
• Temperature Compensated Operation . . . . . . 0oC to 70oC
• Scale Factor, Adjustable. . . . . . . . . . . . . . . . . 1V/Decade
• Dynamic Current Range. . . . . . . . . . . . . . . . . . . . . 120dB
• Dynamic Voltage Range . . . . . . . . . . . . . . . . . . . . . . 60dB
• Dual JFET Input Op Amps
Functional Diagram
ICL8048
fIN
VIN 2
GND 1
VREF
Q1
16
Q2
IREF
-+
A1 A2
+-
VOUT
10
7 15
GAIN
A1 OUTPUT
1 CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 321-724-7143 | Copyright © Intersil Corporation 1999



Intersil Electronic Components Datasheet

ICL8048 Datasheet

Log Amplifier

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ICL8048 pdf
ICL8048
Absolute Maximum Ratings
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±18V
IIN (Input Current) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2mA
IREF (Reference Current). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2mA
Voltage Between Offset Null and V+ . . . . . . . . . . . . . . . . . . . . ±0.5V
Output Short Circuit Duration. . . . . . . . . . . . . . . . . . . . . . . Indefinite
Thermal Information
Thermal Resistance (Typical, Note 1)
θJA (oC/W) θJC (oC/W)
CERDIP Package. . . . . . . . . . . . . . . . .
75
22
Maximum Junction Temperature (Hermetic Package or Die) . . .175oC
Maximum Storage Temperature Range . . . . . . . . . . -65oC to 150oC
Maximum Lead Temperature (Soldering 10s) . . . . . . . . . . . . .300oC
Operating Conditions
Temperature Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0oC to 70oC
Die Characteristics
Number of Transistors or Gates . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
CAUTION: Stresses above those listed in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation of the
device at these or any other conditions above those indicated in the operational sections of this specification is not implied.
NOTE:
1. θJA is measured with the component mounted on an evaluation PC board in free air.
Electrical Specifications VS = ±15V, TA = 25oC, IREF = 1mA, Scale Factor Adjusted for 1V/Decade, Unless Otherwise Specified
ICL4048BC
PARAMETER
TEST CONDITIONS
MIN TYP MAX
UNITS
Dynamic Range
IIN (1nA - 1mA)
VIN (10mV - 10V)
Error, % of Full Scale
Error, Absolute Value
Temperature Coefficient of VOUT
Power Supply Rejection Ratio
RIN = 10k
IIN = 1nA to 1mA
TA = 0oC to 70oC,
IIN = 1nA to 1mA
IIN = 1nA to 1mA
TA = 0oC to 70oC,
IIN = 1nA to 1mA
IIN = 1nA to 1mA
Referred to Output
120 -
-
60 -
-
- 0.20 0.5
- 0.60 1.25
- 12 30
- 36 75
- 0.8 -
- 2.5 -
dB
dB
%
%
mV
mV
mV/oC
mV/V
Offset Voltage (A1 and A2)
Wideband Noise
Output Voltage Swing
Power Consumption
Before Nulling
At Output, for IIN = 100µA
RL = 10k
RL = 2k
- 15 25
- 250 -
±12 ±14
-
±10 ±13
-
- 150 200
mV
µVRMS
V
V
mW
Supply Current
- 5 6.7
mA
Typical Performance Curves
+4
+3
+2
+1
0
-1
-2
-3
-4
1mV
RIN = 10k
IREF = 1mA
IREF = 10µA
IREF = 100nA
10mV
100mV
1V
INPUT VOLTAGE (V)
10V
FIGURE 1. TRANSFER FUNCTION FOR VOLTAGE INPUTS
+8
+6
+4 IREF = 1mA
+2
IREF = 1µA
0
-2 IREF = 1nA
-4
-6
-8
10-10
10-9
10-8 10-7 10-6 10-5
INPUT CURRENT (A)
10-4
10-3
FIGURE 2. TRANSFER FUNCTION FOR CURRENT INPUTS
2



Intersil Electronic Components Datasheet

ICL8048 Datasheet

Log Amplifier

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ICL8048 pdf
ICL8048
Typical Performance Curves (Continued)
100K
IREF = 1mA
10K
1K
100
10
10-11
10-9
10-7
10-5
INPUT CURRENT (A)
FIGURE 3. SMALL SIGNAL BANDWIDTH vs INPUT
CURRENT
10-3
200
175
150
125
100
8048BC (0oC TO 70oC)
75
50
25
0
10-9
10-8
8048BC (25oC)
10-7
10-6
10-5
INPUT CURRENT (A)
10-4
10-3
FIGURE 4. MAXIMUM ERROR VOLTAGE AT THE OUTPUT vs
INPUT CURRENT
200
RIN = 10k
175
150
125
100
8048BC (0oC TO 70oC)
75
50
25
0
10mV
8048BC (25oC)
100mV
1V
INPUT VOLTAGE (V)
10V
FIGURE 5. MAXIMUM ERROR VOLTAGE AT THE OUTPUT vs
INPUT VOLTAGE
ICL8048 Detailed Description
The ICL8048 relies for its operation on the well known
exponential relationship between the collector current and
the base emitter voltage of a transistor:
IC
=
IS
e
x
p
q----V-k---T-B----E--
1
(EQ. 1)
For base emitter voltages greater than 100mV, Equation 1
becomes
IC
=
IS
exp
q----V-k----BT----E--
(EQ. 2)
From Equation 2, it can be shown that for two identical
transistors operating at different collector currents, the VBE
difference (VBE) is given by:
VBE = -2.303 × k--q--T-- log10 II--CC-----12--
(EQ. 3)
1000
434
100
10
VOLTAGE GAIN =
RIN = 10k
VIN
VOUT
=
log10 e
VIN
=
4343
VIN
V/V
1
0.1
0.01
1mV
10mV
100mV
1V
INPUT VOLTAGE (V)
10V
FIGURE 6. SMALL SIGNAL VOLTAGE GAIN vs INPUT
VOLTAGE FOR RS = 10k
Referring to Figure 7 it is clear that the potential at the
collector of Q2 is equal to the VBE between Q1 and Q2. The
output voltage is VBE multiplied by the gain of A2:
VOUT
=
-2.303
-R----1---R--+--2---R----2--
k--q--T--
l
o g10
I--R--I--I-E-N----F--
(EQ. 4)
The expression 2.303
25oC; thus in order to
× k--q--T-- has a numerical
generate 1V/decade
value
at the
of 59mV at
output, the
ratio (R1 + R2)/R2 is chosen to be 16.9. For this scale factor
to hold constant as a function of temperature, the
(R1 + R2)/R2 term must have a 1/T characteristic to
compensate for kT/q.
In the ICL8048 this is achieved by making R1 a thin film
resistor, deposited on the monolithic chip. It has a nominal
value of 15.9kat 25oC, and its temperature coefficient is
3




Part Number ICL8048
Description Log Amplifier
Maker INTERSIL
Total Page 7 Pages
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