MAX4206ETE [MAXIM]
Precision Transimpedance Logarithmic Amplifier with Over 5 Decades of Dynamic Range; 精密阻对数放大器大于10 5的动态范围
| 型号： | MAX4206ETE |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Precision Transimpedance Logarithmic Amplifier with Over 5 Decades of Dynamic Range |
| 文件： | 总17页 (文件大小：1233K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-3071; Rev 0; 12/03
Precision Transimpedance Logarithmic
Amplifier with Over 5 Decades of Dynamic Range
General Description
Features
The MAX4206 logarithmic amplifier computes the log
ratio of an input current relative to a reference current
(externally or internally generated) and provides a cor-
responding voltage output with a default 0.25V/decade
scale factor. The device operates from a single +2.7V
to +11V supply or from dual 2.7V to 5.5V supplies
and is capable of measuring five decades of input cur-
rent across a 10nA to 1mA range.
♦ +2.7V to +11V Single-Supply Operation
♦ ±2.7V to ±5.5V Dual-Supply Operation
♦ 5 Decades of Dynamic Range (10nA to 1mA)
♦ Monotonic Over a 1nA to 1mA Range
♦ 0.25V/Decade Internally Trimmed Output Scale
Factor
The MAX4206’s uncommitted op amp can be used for
a variety of purposes, including filtering noise, adding
offset, and adding additional gain. A 0.5V reference is
also included to generate an optional precision current
reference using an external resistor, which adjusts the
log intercept of the MAX4206. The output-offset voltage
and the adjustable scale factor are also set using exter-
nal resistors.
♦ Adjustable Output Scale Factor
♦ Adjustable Output Offset Voltage
♦ Internal 10nA to 10µA Reference Current Source
♦ 0.5V Input Common-Mode Voltage
♦ Small 16-Pin Thin QFN Package (4mm x 4mm x
0.8mm)
The MAX4206 is available in a space-saving 16-pin thin
QFN package (4mm x 4mm x 0.8mm), and is specified
for operation over the -40°C to +85°C extended temper-
ature range.
♦ -40°C to +85°C Operating Temperature Range
♦ Evaluation Kit Available
Ordering Information
Applications
Photodiode Current Monitoring
Portable Instrumentation
Medical Instrumentation
Analog Signal Processing
PART
TEMP RANGE
PIN-PACKAGE
MAX4206ETE
-40°C to +85°C
16 Thin QFN-EP*
*EP = Exposed Paddle.
Typical Operating Circuit
V
CC
Pin Configuration
I
IN
0.1µF
TOP VIEW
(LEADS ON BOTTOM)
V
CC
V
OUT
LOGV2
SCALE
LOGIIN
R2
C
COMP
16 15 14 13
REFIOUT
REFIIN
R
COMP
C
COMP
N.C.
REFVOUT
GND
1
2
3
4
12 CMVOUT
11 REFISET
R1
MAX4206
R
COMP
MAX4206
10
9
V
CC
CMVIN
CMVOUT
LOGV1
0.1µF
V
EE
N.C.
REFVOUT
REFISET
0.1µF
R
OS
5
6
7
8
OSADJ
GND
V
EE
R
SET
THIN QFN
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Precision Transimpedance Logarithmic
Amplifier with Over 5 Decades of Dynamic Range
ABSOLUTE MAXIMUM RATINGS
(All voltages referenced to GND, unless otherwise noted.)
CMVIN............................................................(V - 0.3V) to +1V
EE
Continuous Current (REFIIN, LOGIIN) ................................10mA
V
V
.........................................................................-0.3V to +12V
............................................................................-6V to +0.3V
CC
EE
Continuous Power Dissipation (T = +70°C)
A
Supply Voltage (V
REFVOUT....................................................(V - 0.3V) to +3.0V
OSADJ, SCALE, REFISET...........................(V - 0.3V) to +5.5V
REFIIN, LOGIIN ........................................(V - 0.3V) to V
to V ) .............................................. +12V
16-Pin Thin QFN (derate 16.9mW/°C above +70°C) ....1349mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature .....................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
CC
EE
EE
EE
EE
CMVIN
LOGV1, LOGV2, CMVOUT,
REFIOUT ......................................(V - 0.3V) to (V
+ 0.3V)
CC
EE
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
DC ELECTRICAL CHARACTERISTICS—Single-Supply Operation
(V
= +5V, V = GND = 0V, I
= -40°C to +85°C. Typical values are at T = +25°C, unless otherwise noted.) (Note 1)
= 1µA, I
= 10µA, LOGV2 = SCALE, LOGV1 = OSADJ, CMVIN = CMVOUT, R > 1MΩ,
CC
EE
REF
LOG
SET
T
A
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
11.0
5
UNITS
Supply Voltage
V
(Note 2)
2.7
V
CC
T
A
T
A
= +25°C
3.9
Supply Current
I
mA
CC
= -40°C to +85°C
7
Minimum
Maximum
Minimum
Maximum
10
10
nA
mA
nA
LOGIIN Current Range (Notes 3, 4)
REFIIN Current Range (Notes 3, 4)
Common-Mode Voltage
I
LOG
1
I
REF
1
mA
V
480
0.5
500
520
mV
V
CMVOUT
Common-Mode Voltage Input
Range
V
1.0
5
CMVIN
I
I
= 10nA,
= 10nA to 1mA,
REF
T
T
= +25°C
2
A
LOG
Log Conformity Error
V
mV
LC
K = 0.25V/decade
(Note 4)
= -40°C to +85°C
10
A
T
T
= +25°C
237.5
250
262.5
A
mV/
decade
Logarithmic Slope (Scale Factor)
K
= -40°C to +85°C (Note 4)
231.25
268.75
A
µV/
decade/
°C
Logarithmic Slope (Scale Factor)
Temperature Drift
T
= -40°C to +85°C
80
1
A
T
A
= +25°C, |V
- V
|,
CMVIN
REFIIN
Input Offset Voltage
V
5
mV
IO
|V
|V
- V |
LOGIIN
CMVIN
Input Offset Voltage Temperature
Drift
V
- V
REFIIN
|, |V
- V |
LOGIIN
6
µV/°C
IOS
CMVIN
CMVIN
T
T
= +25°C
1.218
1.195
1.238
1.258
1.275
A
Voltage Reference Output
V
V
REFVOUT
= -40°C to +85°C (Note 4)
A
Voltage Reference Output Current
Current Reference Output Voltage
I
1
mA
mV
REFVOUT
T
T
= +25°C
490
482
500
510
518
A
V
REFISET
= -40°C to +85°C (Note 4)
A
2
_______________________________________________________________________________________
Precision Transimpedance Logarithmic
Amplifier with Over 5 Decades of Dynamic Range
DC ELECTRICAL CHARACTERISTICS—Single-Supply Operation (continued)
(V
= +5V, V = GND = 0V, I
= -40°C to +85°C. Typical values are at T = +25°C, unless otherwise noted.) (Note 1)
= 1µA, I
= 10µA, LOGV2 = SCALE, LOGV1 = OSADJ, CMVIN = CMVOUT, R > 1MΩ,
CC
EE
REF
LOG
SET
T
A
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
0.4
MAX
UNITS
LOGV2 BUFFER
Input Offset Voltage
Input Bias Current
T
T
= +25°C
2
6
1
A
V
I
mV
nA
IO
= -40°C to +85°C (Note 4)
A
(Note 4)
0.01
B
V
0.2
-
V
0.3
-
CC
CC
V
R to GND = 2kΩ
L
OH
Output Voltage Range
V
V
R to GND = 2kΩ
0.2
0.08
34
58
12
5
OL
L
I
Sourcing
Sinking
OUT+
Output Short-Circuit Current
mA
I
OUT-
Slew Rate
SR
V/µs
MHz
Unity-Gain Bandwidth
GBW
AC ELECTRICAL CHARACTERISTICS—Single-Supply Operation
(V
= +5V, V = GND = 0, I
= +25°C, unless otherwise noted.)
= 1µA, I
= 10µA, LOGV2 = SCALE, LOGV1 = OSADJ, CMVIN = CMVOUT, R > 1MΩ,
CC
EE
REF
LOG
SET
T
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
0.1Hz to 10Hz, total output-referred noise,
LOGV2 Total Noise
17
µV
RMS
I
= 10nA, I
= 100nA
REF
LOG
LOGV2 Spot Noise Density
REFVOUT Total Noise
f = 5kHz, I
= 10nA, I
= 100nA
0.8
3.3
µV/√Hz
µV
REF
LOG
1Hz to 10Hz, total output-referred noise
f = 5kHz
RMS
REFVOUT Spot Noise Density
REFISET Total Noise
266
0.67
23
nV/√Hz
µV
1Hz to 10Hz, total output-referred noise
f = 5kHz
RMS
REFISET Spot Noise Density
nV/√Hz
Small-Signal Unity-Gain
Bandwidth
I
C
= 1µA, I
= 10µA, R
= 300Ω,
REF
LOG
COMP
1
MHz
= 32pF
COMP
DC ELECTRICAL CHARACTERISTICS—Dual-Supply Operation
(V
= +5V, V = -5V, GND = 0, I
= -40°C to +85°C. Typical values are at T = +25°C, unless otherwise noted.) (Note 1)
= 1µA, I
= 10µA, LOGV2 = SCALE, LOGV1 = OSADJ, CMVIN = CMVOUT, R > 1MΩ,
CC
EE
REF
LOG
SET
T
A
A
PARAMETER
SYMBOL
CONDITIONS
MIN
2.7
TYP
MAX
5.5
-5.5
6
UNITS
V
CC
Supply Voltage (Note 2)
Supply Current
V
V
-2.7
EE
T
T
= +25°C
5
A
I
mA
CC
= -40°C to +85°C
7.5
A
Minimum
Maximum
Minimum
Maximum
10
10
nA
mA
nA
LOGIIN Current Range (Notes 3, 4)
I
LOG
1
REFIIN Current Range (Notes 3, 4)
Common-Mode Voltage
I
REF
1
mA
V
480
500
520
mV
CMVOUT
_______________________________________________________________________________________
3
Precision Transimpedance Logarithmic
Amplifier with Over 5 Decades of Dynamic Range
DC ELECTRICAL CHARACTERISTICS—Dual-Supply Operation (continued)
(V
= +5V, V = -5V, GND = 0, I
= -40°C to +85°C. Typical values are at T = +25°C, unless otherwise noted.) (Note 1)
= 1µA, I
= 10µA, LOGV2 = SCALE, LOGV1 = OSADJ, CMVIN = CMVOUT, R > 1MΩ,
CC
EE
REF
LOG
SET
T
A
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
2
MAX
UNITS
Common-Mode Voltage Input
Range
V
0.5
1.0
V
CMVIN
I
I
= 10nA,
REF
T
T
= +25°C
5
A
= 10nA to 1mA,
K = 0.25V/decade
(Note 4)
LOG
Log Conformity Error
V
mV
LC
= -40°C to +85°C
10
A
T
T
= +25°C
237.5
250
262.5
A
mV/
decade
Logarithmic Slope (Scale Factor)
K
= -40°C to +85°C
231.25
268.75
A
µV/
decade/
°C
Logarithmic Slope (Scale Factor)
Temperature Drift
T
= -40°C to +85°C
80
1
A
T
= +25°C, |V
- V
|,
A
CMVIN
REFIIN
Input Offset Voltage
V
5
mV
µV/°C
V
IO
|V
|V
- V |
LOGIIN
CMVIN
Input Offset Voltage
Temperature Drift
V
- V
REFIIN
|, |V
- V |
LOGIIN
6
IOS
CMVIN
CMVIN
T
T
= +25°C
1.218
1.195
1.238
1.258
1.275
A
Voltage Reference Output
V
REFVOUT
= -40°C to +85°C (Note 4)
A
Voltage Reference Output
Current
I
1
mA
mV
REFVOUT
T
T
= +25°C
490
482
500
510
518
A
Current Reference Output
Voltage
V
REFISET
= -40°C to +85°C (Note 4)
A
LOGV2 BUFFER
Input Offset Voltage
Input Bias Current
T
T
= +25°C
0.4
2
6
1
A
V
I
mV
nA
IO
= -40°C to +85°C (Note 4)
A
(Note 4)
0.01
B
V
0.2
-
V
0.3
-
CC
CC
V
R to GND = 2kΩ
L
OH
Output Voltage Range
V
V
+
0.2
V
+
EE
EE
V
R to GND = 2kΩ
OL
L
0.08
34
58
12
5
I
Sourcing
Sinking
OUT+
Output Short-Circuit Current
mA
I
OUT-
SR
Slew Rate
V/µs
MHz
Unity-Gain Bandwidth
GBW
4
_______________________________________________________________________________________
Precision Transimpedance Logarithmic
Amplifier with Over 5 Decades of Dynamic Range
AC ELECTRICAL CHARACTERISTICS—Dual-Supply Operation
(V
= +5V, V = -5V, GND = 0, I
= +25°C, unless otherwise noted.)
= 1µA, I
= 10µA, LOGV2 = SCALE, LOGV1 = OSADJ, CMVIN = CMVOUT, R > 1MΩ,
CC
EE
REF
LOG
SET
T
A
PARAMETER
SYMBOL
CONDITIONS
0.1Hz to 10Hz, total output-referred noise,
= 10nA, I = 100nA
MIN
TYP
MAX
UNITS
LOGV2 Total Noise
17
µV
RMS
I
REF
LOG
LOGV2 Spot Noise Density
REFVOUT Total Noise
f = 5kHz, I
= 10nA, I
= 100nA
0.8
3.3
µV/√Hz
µV
REF
LOG
1Hz to 10Hz, total output-referred noise
f = 5kHz
RMS
REFVOUT Spot Noise Density
REFISET Total Noise
266
0.67
23
nV/√Hz
µV
1Hz to 10Hz, total output-referred noise
f = 5kHz
RMS
REFISET Spot Noise Density
nV/√Hz
Small-Signal Unity-Gain
Bandwidth
I
C
= 1µA, I
= 10µA, R
= 300Ω,
REF
LOG
COMP
1
MHz
= 32pF
COMP
Note 1: All devices are 100% production tested at T = +25°C. All temperature limits are guaranteed by design.
A
Note 2: Guaranteed and functionally verified.
Note 3: Log conformity error less than 5mV with scale factor = 0.25V/decade.
Note 4: Guaranteed by design.
Typical Operating Characteristics
(V
= +5V, V = GND = 0V, I
= 1µA, I
= 10µA, LOGV2 = SCALE, LOGV1 = OSADJ, CMVIN = CMVOUT, R
> 1MΩ,
CC
EE
REF
LOG
SET
T
A
= +25°C, unless otherwise noted.)
V
vs. I
LOG
LOGV1
V
vs. I
LOGV1 LOG
V
vs. I
LOG
LOGV1
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
I
T
V
V
= 10nA
= -40 C TO +85 C
= +5V
I
T
V
V
= 10nA
= -40 C TO +85 C
= +5V
REF
A
CC
EE
I
T
V
V
= 10nA
= -40 C TO +85 C
= +2.7V
REF
A
CC
EE
REF
A
CC
EE
°
°
°
°
°
°
= GND
= -5V
= GND
-0.25
-0.25
-0.25
10n 100n
1µ
10µ 100µ 1m
10m
1n 10n 100n 1µ 10µ 100µ 1m 10m
(A)
10n
100n
1µ
10µ 100µ
1m
10m
I
(A)
I
LOG
I
(A)
LOG
LOG
_______________________________________________________________________________________
5
Precision Transimpedance Logarithmic
Amplifier with Over 5 Decades of Dynamic Range
Typical Operating Characteristics (continued)
(V
= +5V, V = GND = 0V, I
= 1µA, I
= 10µA, LOGV2 = SCALE, LOGV1 = OSADJ, CMVIN = CMVOUT, R
> 1MΩ,
CC
EE
REF
LOG
SET
T
A
= +25°C, unless otherwise noted.)
V
REF
vs. I
LOG
= 10nA TO 1mA)
NORMALIZED LOG CONFORMANCE
V
LOG
vs. I
REF
= 10nA TO 1mA)
LOGV1
LOGV1
(I
ERROR vs. I
(I
LOG
2.00
2.0
1.8
1.5
1.3
1.0
0.8
0.5
0.3
0
20
15
10
5
I
T
V
V
= 10nA
= -40 C TO +85 C
= +5V
= GND
REF
A
CC
EE
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
° °
1mA
100µA
10µA
1µA
100nA
10nA
0
-5
1mA
-10
-15
-20
10nA
10µA 100µA
100nA 1µA
-0.25
-0.50
-0.3
-0.5
10n 100n
1µ
10µ 100µ 1m
(A)
10m
1n
10n 100n
1µ
(A)
10µ 100µ 1m
10n 100n
1µ
10µ 100µ 1m
I (A)
LOG
10m
I
LOG
I
REF
NORMALIZED LOG CONFORMANCE
NORMALIZED LOG CONFORMANCE
NORMALIZED LOG CONFORMANCE
ERROR vs. I
ERROR vs. I
ERROR vs. I
LOG
LOG
LOG
20
15
10
5
20
15
10
5
20
15
10
5
I
T
V
V
= 10nA
= -40 C TO +85 C
= +2.7V
I
= 10nA
I
T
V
V
= 10nA
= -40 C TO +85 C
= +5V
REF
A
CC
EE
REF
REF
A
CC
EE
°
°
°
°
SINGLE SUPPLY: V = +2.7V, +5V, 11V,
V = GND
EE
DUAL SUPPLY: V = +5V
V
CC
= GND
= -5V
CC
= -5V
EE
0
0
0
-5
-5
-5
-10
-15
-20
°
-10
-15
-20
-10
-15
-20
T
A
= -40 C
°
T = -40 C
A
1n 10n 100n 1µ 10µ 100µ 1m 10m
10n 100n
1µ
10µ 100µ 1m
(A)
10m
10n 100n
1µ
10µ 100µ 1m
I (A)
LOG
10m
I
(A)
I
LOG
LOG
V
VOLTAGE-NOISE DENSITY
vs. FREQUENCY
TOTAL WIDEBAND VOLTAGE NOISE
AT V vs. I
LOGV2
V
- V
vs. I
CMVIN LOG
LOGIIN
LOGV2
LOG
10
1
5
4
3
2
1
0
5
I
= 10nA
10nA
REF
I
= I
REF LOG
4
3
2
f = 1Hz TO 1MHz
100nA
1µA
1
0
10µA
-1
-2
-3
-4
-5
0.1
0.01
I
= I
REF LOG
1
10 100 1k
10k 100k 1M 10M
10n
100n
1µ
10µ
(A)
100µ
1m
1n 10n 100n 1µ 10µ 100µ 1m 10m
(A)
FREQUENCY (Hz)
I
I
LOG
LOG
6
_______________________________________________________________________________________
Precision Transimpedance Logarithmic
Amplifier with Over 5 Decades of Dynamic Range
Typical Operating Characteristics (continued)
(V
= +5V, V = GND = 0V, I
= 1µA, I
= 10µA, LOGV2 = SCALE, LOGV1 = OSADJ, CMVIN = CMVOUT, R
> 1MΩ,
CC
EE
REF
LOG
SET
T
A
= +25°C, unless otherwise noted.)
I
PULSE RESPONSE
I
PULSE RESPONSE
LOG
LOG
(I
= 100nA,
(I
= 100nA,
REF
REF
V
= 5V, V = GND)
V
= 5V, V = -5V)
CC EE
CC
EE
MAX4206 toc13
MAX4206 toc14
1.0V
0.75V
0.75V
0.50V
0.50V
0.25V
0.25V
0
1.0V
0.75V
0.75V
0.50V
0.50V
0.25V
0.25V
0
100µA TO 1mA
10µA TO 100µA
100µA TO 1mA
10µA TO 100µA
1µA TO 10µA
100nA TO 1µA
1µA TO 10µA
100nA TO 1µA
20µs/div
20µs/div
I
PULSE RESPONSE
REF
(I
= 1mA)
LOGARITHMIC SLOPE DISTRIBUTION
LOG
MAX4206 toc15
30
25
20
15
10
5
1.0V
0.75V
0.75V
0.50V
0.50V
0.25V
0.25V
0
1µA TO 100nA
10µA TO 1µA
100µA TO 10µA
1mA TO 100µA
0
260
240
245
250
255
SLOPE (mV/decade)
20µs/div
V
DISTRIBUTION
REFVOUT
INPUT OFFSET VOLTAGE DISTRIBUTION
25
20
15
16
14
12
10
8
R = 100kΩ
L
INPUT OFFSET VOLTAGE = V
- V
CMVIN
LOGIIN
10
5
6
4
2
0
0
1.244
1.232 1.234 1.236 1.238 1.240 1.242
3.0
-1.0 -0.5
0
0.5 1.0 1.5 2.0 2.5
V
(V)
REFVOUT
INPUT OFFSET VOLTAGE (mV)
_______________________________________________________________________________________
7
Precision Transimpedance Logarithmic
Amplifier with Over 5 Decades of Dynamic Range
Typical Operating Characteristics (continued)
(V
= +5V, V = GND = 0V, I
= 1µA, I
= 10µA, LOGV2 = SCALE, LOGV1 = OSADJ, CMVIN = CMVOUT, R
> 1MΩ,
CC
EE
REF
LOG
SET
T
A
= +25°C, unless otherwise noted.)
REFERENCE OUTPUT VOLTAGE (V
vs. TEMPERATURE
)
REFERENCE OUTPUT VOLTAGE (V
vs. LOAD CURRENT
)
REFERENCE OUTPUT VOLTAGE (V
)
REFVOUT
REFVOUT
REFVOUT
vs. SUPPLY VOLTAGE
1.30
1.29
1.28
1.27
1.26
1.25
1.24
1.23
1.22
1.21
1.20
1.50
1.250
1.245
1.240
1.235
1.230
1.225
1.220
1.215
1.210
1.205
1.200
1.45
1.40
1.35
1.30
1.25
1.20
1.15
1.10
1.05
1.00
-50
-25
0
25
50
75
100
-1.0
-0.5
0
0.5
1.0
2
3
4
5
6
°
TEMPERATURE ( C)
LOAD CURRENT (mA)
SUPPLY VOLTAGE (V)
REFERENCE POWER-SUPPLY
REJECTION RATIO vs. FREQUENCY
REFERENCE LINE-TRANSIENT RESPONSE
MAX4206 toc23
0
C
= 0.1µF
REFVOUT
REFVOUT
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
I
= 1mA
V
CC
2V/div
0V
V
REFVOUT
200mV/div
1.238V
C
= 0F
REFVOUT
10
100
1k
10k
100k
1M
10µs/div
FREQUENCY (Hz)
REFERENCE LOAD-TRANSIENT RESPONSE
REFERENCE TURN-ON TRANSIENT RESPONSE
MAX4206 toc25
MAX4206 toc24
C
= 0F
REFVOUT
I
V
CC
2.5V/div
REFVOUT
0mA
1mA/div
0V
0V
V
V
REFVOUT
500mV/div
REFVOUT
1.238V
100mV/div
100µs/div
10µs/div
8
_______________________________________________________________________________________
Precision Transimpedance Logarithmic
Amplifier with Over 5 Decades of Dynamic Range
Typical Operating Characteristics (continued)
(V
= +5V, V = GND = 0V, I
= 1µA, I
= 10µA, LOGV2 = SCALE, LOGV1 = OSADJ, CMVIN = CMVOUT, R
> 1MΩ,
CC
EE
REF
LOG
SET
T
A
= +25°C, unless otherwise noted.)
SMALL-SIGNAL AC RESPONSE
OF BUFFER
SMALL-SIGNAL AC RESPONSE
SMALL-SIGNAL AC RESPONSE
I
TO V
I
TO V
LOG
LOGV1
LOG
LOGV1
10
0
3
0
10
0
I
= 1mA
LOG
I
= 100µA
LOG
A
V
= 1V/V
I
= 1mA
I
= 100µA
LOG
LOG
-10
-20
-30
-40
-50
-60
-10
-20
-30
-40
-50
-60
A
= 2V/V
V
I
= 10µA
LOG
-3
I
= 10µA
= 1µA
LOG
I
= 1µA
LOG
A
= 4V/V
V
-6
I
LOG
I
= 100nA
LOG
I
= 100nA
LOG
-9
C
R
= 33pF
= 330Ω
C
R
= 100pF
= 1kΩ
COMP
COMP
COMP
COMP
-12
100
1k
10k
100k
1M
10M
10k
100k
1M
FREQUENCY (Hz)
10M
100M
100
1k
10k
100k
1M
10M
FREQUENCY (Hz)
FREQUENCY (Hz)
Pin Description
PIN
1, 9
2
NAME
N.C.
FUNCTION
No Connection. Not internally connected.
REFVOUT
GND
1.238V Reference Voltage Output. Bypass REFVOUT to GND with a 0 to 1µF capacitor (optional).
Ground
3
4
V
Negative Power Supply. Bypass V to GND with a 0.1µF capacitor.
EE
EE
5
LOGV1
Logarithmic Amplifier Voltage Output 1. The output scale factor of LOGV1 is 0.25V/decade.
Offset Adjust Input. When operating from a single power supply, current applied to OSADJ adjusts
the output offset voltage (see the Output Offset section).
6
7
OSADJ
Scale Factor Input. Adjust the output scale factor for LOGV2 using a resistive divider (see the Scale
Factor section).
SCALE
LOGV2
Logarithmic Amplifier Voltage Output 2. Adjust the output scale factor for LOGV2 using a resistive
divider (see the Scale Factor section).
8
10
11
V
Positive Power Supply. Bypass V
to GND with a 0.1µF capacitor.
CC
CC
Current Reference Adjust Input. A resistor, R , from REFISET to GND adjusts the current at
SET
REFIOUT (see the Adjusting the Logarithmic Intercept section).
REFISET
12
13
CMVOUT
REFIOUT
0.5V Common-Mode Voltage Reference Output. Bypass CMVOUT to GND with a 0.1µF capacitor.
Current Reference Output. The internal current reference output is available at REFIOUT.
Current Reference Input. Apply an external reference current at REFIIN. I
current used by the logarithmic amplifier when generating LOGV1.
is the reference
REFIIN
14
15
16
REFIIN
LOGIIN
CMVIN
Current Input to Logarithmic Amplifier. LOGIIN is typically connected to a photodiode anode or other
external current source.
Common-Mode Voltage Input. V
is the common-mode voltage for the input and reference
CMVIN
amplifiers (see the Common Mode section).
_______________________________________________________________________________________
9
Precision Transimpedance Logarithmic
Amplifier with Over 5 Decades of Dynamic Range
REFVOUT
1.238V
CMVOUT
V
CC
CURRENT MIRROR
REFIOUT
V
CC
CURRENT
CORRECTION
V
CC
LOGIIN
CMVIN
0.5V
V
EE
REFISET
LOGV2
V
CC
V
CC
REFIIN
SUMMING
AMPLIFIER
SCALE
AND
TEMPERATURE
COMPENSATION
OSADJ
LOGV1
V
EE
V
EE
GND
MAX4206
Figure 1. Functional Diagram
dencies of a logarithmic amplifier relate to the thermal
Detailed Description
voltage, (KT/q), and I . Matched transistors eliminate
S
Theory
Figure 2 shows a simplified model of a logarithmic
amplifier. Two transistors convert the currents applied
at LOGIIN and REFIIN to logarithmic voltages accord-
ing to the following equation:
the I temperature dependence of the amplifier in the
S
following manner:
V
= V
− V
OUT
BE1 BE2
I
REF
kT
q
I
kT
q
LOG
=
=
=
=
ln
−
ln
kT
q
I
C
I
I
S
S
V
=
ln
BE
I
S
I
REF
kT
q
I
LOG
ln
−ln
I
I
S
S
where:
V
BE
= base-emitter voltage of a bipolar transistor
k = 1.381 x 10-23 J/K
kT
q
I
LOG
ln
I
REF
T = absolute temperature (K)
kT
q
I
LOG
q = 1.602 x 10 –19
C
ln(10) log
(
)
10
I
REF
I = collector current
C
I
I
LOG
I = reverse saturation current
S
=K × log
(see Figure 3)
10
REF
The logarithmic amplifier compares V
to the refer-
BE1
ence voltage V
, which is a logarithmic voltage for a
BE2
known reference current, I . The temperature depen-
REF
10 ______________________________________________________________________________________
Precision Transimpedance Logarithmic
Amplifier with Over 5 Decades of Dynamic Range
IDEAL TRANSFER FUNCTION
V
BE1
WITH VARYING K
V
CC
I
LOG
4
3
LOGIIN
CMVIN
K = 1
K = 0.5
K = 0.25
V
OUT
= K LOG (I /I
)
LOG REF
2
1
V
EE
0
-1
-2
-3
V
BE2
V
CC
I
REF
REFIIN
-4
0.001
0.1
10
1000
V
EE
CURRENT RATIO (I /I
)
LOG REF
Figure 2. Simplified Model of a Logarithmic Amplifier
Figure 3. Ideal Transfer Function with Varying K
where:
Referred-to-Input and Referred-to-Output Errors
The log nature of the MAX4206 insures that any addi-
tive error at LOGV1 corresponds to multiplicative error
at the input, regardless of input level.
K = scale factor (V/decade)
I
= the input current at LOGIIN
LOG
REF
I
= the reference current at REFIIN
Total Error
The MAX4206 uses internal temperature compensation
to virtually eliminate the effects of the thermal voltage,
(kT/q), on the amplifier’s scale factor, maintaining a
constant slope over temperature.
Total error, TE, is defined as the deviation of the output
voltage, V
, from the ideal transfer function (see
LOGV1
the Ideal Transfer Function section):
V
= V ± TE
LOGV1
IDEAL
Definitions
Transfer Function
The ideal logarithmic amplifier transfer function is:
Total error is a combination of the associated gain,
input offset current, input bias current, output offset
voltage, and transfer characteristic nonlinearity (log
conformity) errors:
I
I
LOG
V
=K × log
10
IDEAL
REF
I
−I
−I
LOG BIAS1
V
=K(1± ∆K) log
± 4 ±V ± V
LC OSOUT
(
)
LOGV2
10
I
Adjust K (see the Scale Factor section) to increase the
REF BIAS2
transfer-function slope as illustrated in Figure 3. Adjust
I
using REFISET (see the Adjusting the Logarithmic
where V and V
are the log conformity and out-
OSOUT
REF
LC
Intercept section) to shift the logarithmic intercept to the
put offset voltages, respectively. Output offset is
defined as the offset occurring at the output of the
left or right as illustrated in Figure 4.
MAX4206 when equal currents are presented to I
LOG
Log Conformity
Log conformity is the maximum deviation of the
MAX4206’s output from the best-fit straight line of the
) curve. It is expressed as
a percent of the full-scale output or an output voltage.
and I
. Because the MAX4206 is configured with
REF
a gain of K = 0.25V/decade, a 4 should multiply the
( V ) term, if V and V were derived
V
LC
OSOUT
LC
OSOUT
V
versus log (I
/I
LOGV1
LOG REF
from this default configuration.
______________________________________________________________________________________ 11
Precision Transimpedance Logarithmic
Amplifier with Over 5 Decades of Dynamic Range
I
and I
are currents on the order of 20pA,
BIAS2
BIAS1
significantly smaller than I
fore be eliminated:
and I
, and can there-
REF
LOG
IDEAL TRANSFER FUNCTION
WITH VARYING I
REF
I
I
LOG
1.5
1.0
0.5
0
V
≅K(1± ∆K) log
±4 ±V ±V
(
)
LOGV2
10
LC
OSOUT
REF
I
= 10nA
REF
Expanding this expression:
I
I
LOG
LOG
V
≅Klog
±K∆Klog
10
LOGV2
10
I
I
REF
REF
± 4K(1± ∆K) ±V ±V
-0.5
-1.0
LC
OSOUT
I
= 100µA
100µ
REF
I
= 1µA
REF
The first term of this expression is the ideal component
of V . The remainder of the expression is the total
LOGV1
error, TE:
-1.5
1n
10n 100n
1µ
10µ
1m
I
(A)
I
I
LOG
LOG
TE ≅ ±K∆Klog
± 4K(1± ∆K) ±V ±V
OSOUT
(
)
10
LC
REF
In the second term, one can generally remove the
products relating to ∆K, because ∆K is generally much
less than 1. Hence, a good approximation for TE is
given by:
Figure 4. Ideal Transfer Function with Varying I
REF
tributing to total error. For further accuracy, consider tem-
perature monitoring as part of the calibration process.
I
I
Applications Information
Input Current Range
Five decades of input current across a 10nA to 1mA
LOG
TE ≅ ±K ∆Klog
± 4 ±V ±V
LC OSOUT
(
)
10
REF
As an example, consider the following situation:
Full-scale input = 5V
range are acceptable for I
and I
LOG
. The effects of
REF
LOG
leakage currents increase as I
and I
fall below
REF
10nA. Bandwidth decreases at low I
values (see
LOG
I
I
= 100µA
= 100nA
LOG
REF
the Frequency Response and Noise Considerations
section). As I and I increase to 1mA or higher,
LOG
REF
K = 1 5% V/decade (note that the uncommitted ampli-
fier is configured for a gain of 4)
transistors become less logarithmic in nature. The
MAX4206 incorporates leakage current compensation
and high-current correction circuits to compensate for
these errors.
V
=
5mV (obtained from the Electrical Character-
istics table)
LC
V
= 2mV (typ)
OSOUT
Frequency Compensation
The MAX4206’s frequency response is a function of the
input current magnitude and the selected compensation
network at LOGIIN and REFIIN. The compensation net-
T = +25°C
A
Substituting into the total error approximation,
TE ≅
(1V/decade)(0.05log10 (100µA/100nA)
4 ( 5mV 2mV) = ꢀ0.15V 4( 7mV)ꢁ
work comprised of C
and R
ensures stability
COMP
COMP
over the specified range of input currents by introducing
an additional pole/zero to the system. For the typical
As a worst case, one finds TE ≅ 178mV or 3.6% of
full scale.
application, select C
= 100pF and R
= 100Ω.
COMP
COMP
Where high bandwidth at low current is required, C
COMP
When expressed as a voltage, TE increases in proportion
with an increase in gain as the contributing errors are
defined at a specific gain. Calibration using a look-up
table eliminates the effects of gain and output offset
errors, leaving conformity error as the only factor con-
= 32pF and R
sation values.
= 330Ω are suitable compen-
COMP
12 ______________________________________________________________________________________
Precision Transimpedance Logarithmic
Amplifier with Over 5 Decades of Dynamic Range
Frequency Response and Noise Considerations
The MAX4206 bandwidth is proportional to the magni-
Select R1 between 1kΩ and 100kΩ, with an ideal value
of 10kΩ. The noninverting amplifier ensures that the
overall scale factor is greater than or equal to
0.25V/decade for single-supply operation.
tude of the I
and I
currents, whereas the noise is
LOG
REF
inversely proportional to I
and I
currents.
LOG
REF
Common Mode
, of 0.5V is
Design Example
A common-mode input voltage, V
Desired:
CMVOUT
available at CMVOUT and can be used to bias the log-
ging and reference amplifier inputs by connecting
CMVOUT to CMVIN. An external voltage between 0.5V
and 1V can be applied to CMVIN to bias the logging
and reference transistor collectors and to optimize the
performance required for both single- and dual-supply
operation.
Single-Supply Operation
Logarithmic intercept: 100nA
Overall scale factor = 1V/decade
Because there is no offset current applied to the circuit
(R
= 0Ω), the reference current, I
, equals the log
REF
OS
intercept of 100µA. Therefore,
Adjusting the Logarithmic Intercept
0.5V
10×100nA
R
=
= 500kΩ
SET
Adjust the logarithmic intercept by changing the refer-
ence current, I
. A resistor from REFISET to GND
REF
Select R = 10kΩ:
(see Figures 5 and 6) adjusts the reference current,
according to the following equation:
1
1V/V
0.25
R2 =10kΩ
−1 = 30kΩ
V
10×I
REFISET
R
=
SET
REF
Dual-Supply Operation
When operating from dual 2.7 to 5.5V supplies, it is
not required that I be greater than I . A positive
where V
is 0.5V. Select R
between 5kΩ and
REFISET
SET
5MΩ. REFIOUT current range is 10nA to 10µA only.
LOG
REF
output voltage results at LOGV1 when I
exceeds
LOG
Single-Supply Operation
I
I
. A negative output voltage results at LOGV1 when
REF
LOG
When operating from a single +2.7V to +11V supply,
is less than I
. Bias the log and reference
REF
I
must be greater than I
, resulting in a positive
REF
LOG
amplifiers by connecting CMVOUT to CMVIN or con-
nect an external 0.5V to 1V reference to CMVIN. For
dual-supply operation with CMVIN < 0.5V, refer to the
MAX4207 data sheet.
slope of the log output voltages, LOGV1 and LOGV2.
Bias the log and reference amplifiers by connecting
CMVOUT to CMVIN or connecting an external voltage
reference between 0.5V and 1V to CMVIN. For single-
supply operation, connect V to GND.
EE
Output Offset
The uncommitted amplifier in the inverting configuration
utilized by the MAX4206 facilitates large output-offset
voltage adjustments when operated with dual supplies.
The magnitude of the offset voltage is given by the fol-
lowing equation:
Output Offset
to adjust the output offset voltage
Select R
and I
OS
OS
(see Figure 5). The magnitude of the offset voltage is
given by:
V
OS
= R
♦ I
OS OSADJ
Scale Factor
R
R
2
V
= V
1+
OS
OSADJ
The scale factor, K, is the slope of the logarithmic out-
put. For the LOGV1 amplifier, K = 0.25V/decade. When
operating in a single-supply configuration, adjust the
overall scale factor for the MAX4206 using the uncom-
mitted LOGV2 amplifier and the following equation,
which refers to Figure 5:
1
A resistive divider between REFVOUT, OSADJ, and
GND can be used to adjust V
(see Figure 6).
OSADJ
R
4
V
= V
REFOUT
OSADJ
R +R
3
4
K
0.25
R2 =R1
−1
______________________________________________________________________________________ 13
Precision Transimpedance Logarithmic
Amplifier with Over 5 Decades of Dynamic Range
V
CC
V
CC
CC
I
IN
I
IN
0.1µF
V
CC
V
OUT
0.1µF
V
LOGV2
SCALE
V
OUT
LOGV2
SCALE
LOGIIN
R2
40kΩ
LOGIIN
C
COMP
100pF
R2
30kΩ
C
100pF
COMP
REFIOUT
REFIIN
R
COMP
REFIOUT
REFIIN
100Ω
R
COMP
C
COMP
100pF
100Ω
R1
10kΩ
C
100pF
COMP
R1
10kΩ
MAX4206
R
COMP
LOGV1
MAX4206
100Ω
R
COMP
100Ω
REFVOUT
CMVIN
CMVOUT
LOGV1
0.1µF
CMVIN
R3
R4
REFVOUT
REFISET
0.1µF
CMVOUT
0.1µF
OSADJ
R
0Ω
OS
REFISET
OSADJ
GND
V
V
EE
R
SET
GND
V
EE
50kΩ
R
SET
500kΩ
0.1µF
EE
Figure 5. Single-Supply Typical Operating Circuit
Figure 6. Dual-Supply Typical Operating Circuit
Scale Factor
The scale factor, K, is the slope of the logarithmic output.
For the LOGV1 amplifier, K = 0.25V/decade. When oper-
ating from dual supplies, adjust the overall scale factor
for the MAX4206 using the uncommitted LOGV2 amplifi-
er and the following equation, which refers to Figure 6:
Measuring Optical Absorbance
A photodiode provides a convenient means of measur-
ing optical power, as diode current is proportional to
the incident optical power. Measure absolute optical
power using a single photodiode connected at LOGIIN,
with the MAX4206’s internal current reference driving
REFIIN. Alternatively, connect a photodiode to each of
the MAX4206’s logging inputs, LOGIIN and REFIIN, to
measure relative optical power (Figure 7).
K
R =R
2
1
0.25
In absorbance measurement instrumentation, a refer-
ence light source is split into two paths. The unfiltered
path is incident upon the photodiode of the reference
channel, REFIIN. The other path passes through a sam-
ple of interest, with the resulting filtered light incident on
the photodiode of the second channel, LOGIIN. The
MAX4206 outputs provide voltages proportional to the
log ratio of the two optical powers—an indicator of the
optical absorbance of the sample.
Select R between 1kΩ and 100kΩ.
2
Design Example
Desired:
Dual-Supply Operation
Logarithmic intercept: 1µA
Overall scale factor = 1V/decade
0.5V
In wavelength-locking applications, often found in
fiberoptic communication modules, two photodiode cur-
rents provide a means of determining whether a given
optical channel is tuned to the desired optical frequency.
In this application, two bandpass optical filters with over-
lapping “skirts” precede each photodiode. With proper fil-
ter selection, the MAX4206 output can vary monotonically
(ideally linearly) with optical frequency.
R
=
= 50kΩ
SET
10×1µA
Select R = 10kΩ:
1
1V/decade
0.25
R2 =10kΩ ×
= 40kΩ
14 ______________________________________________________________________________________
Precision Transimpedance Logarithmic
Amplifier with Over 5 Decades of Dynamic Range
Photodiode Current Monitoring
V
CC
Figure 8 shows the MAX4206 in a single-supply, optical-
power measurement circuit, common in fiberoptic
applications. The MAX4007 current monitor converts
the sensed APD current to an output current that drives
the MAX4206 LOGIIN input (APD current is scaled by
0.1). The MAX4007 also buffers the high-voltage APD
voltages from the lower MAX4206 voltages. The
MAX4206’s internal current reference sources 10nA
0.1µF
V
CC
CMVIN
0.1µF
REFISET
REFIIN
CMVOUT
REFVOUT
LOGV2
100pF
0.1µF
V
CC
(R
= 5MΩ) to the REFIIN input. This configuration
SET
R
R
2
MAX4206
100Ω
sets the logarithmic intercept to 10nA, corresponding to
an APD current of 100nA. The unity-gain configuration
of the output buffer maintains the 0.25V/decade gain
present at the LOGV1 output.
SCALE
LOGV1
R
1
LOGIIN
3
Capacitive Loads
The MAX4206 drives capacitive loads of up to 50pF.
Reactive loads decrease phase margin and can pro-
duce excessive ringing and oscillation. Use an isolation
resistor in series with LOGV1 or LOGV2 to reduce the
effect of large capacitive loads. Recall that the combi-
nation of the capacitive load and the small isolation
resistor limits AC performance.
100pF
OSADJ
REFIOUT
100Ω
R
4
V
EE
GND
Figure 7. Measuring Optical Absorbance
Power Dissipation
The LOGV1 and LOGV2 amplifiers are capable of
sourcing or sinking in excess of 30mA. Ensure that the
continuous power dissipation rating for the MAX4206 is
not exceeded.
noise immunity and a clean reference current. For low-
current operation, it is recommended to use metal
guard rings around LOGIIN, REFIIN, and REFISET.
Connect this guard ring to CMVOUT.
TQFN Package
The 16-lead thin QFN package has an exposed paddle
that provides a heat-removal path, as well as excellent
electrical grounding to the PC board. The MAX4206’s
Evaluation Kit
An evaluation kit is available for the MAX4206. The kit is
flexible and can be configured for either single-supply or
dual-supply operation. The scale factor and reference
current are selectable. Refer to the MAX4206 Evaluation
Kit data sheet for more information.
exposed pad is internally connected to V , and can
EE
either be connected to the PC board V plane or left
EE
unconnected. Ensure that only V
under the exposed paddle.
traces are routed
EE
Chip Information
TRANSISTOR COUNT: 754
Layout and Bypassing
Bypass V
and V
to GND with ceramic 0.1µF
EE
CC
capacitors. Place the capacitors as close to the device
as possible. Bypass REFVOUT and/or CMVOUT to
GND with a 0.1µF ceramic capacitor for increased
PROCESS: BiCMOS
______________________________________________________________________________________ 15
Precision Transimpedance Logarithmic
Amplifier with Over 5 Decades of Dynamic Range
V
CC
2.2µH
2.2µF
+2.7V TO +76V
PHOTODIODE BIAS
0.22µF
0.1µF
0.1µF
V
CC
BIAS
CLAMP
OUTPUT
REFVOUT
REFIOUT
REFIIN
LOGV2
SCALE
MAX4007
MAX4206
100pF
LOGV1
OSADJ
100Ω
REFISET
I /10
APD
I
APD
5MΩ
REF
OUT
100pF
CMVOUT
CMVIN
GND
TIA
100Ω
0.1µF
FIBER CABLE
APD
GND
V
EE
TO LIMITING
AMPLIFIER
HIGH-SPEED DATA PATH
Figure 8. Logarithmic Current-Sensing Amplifier with Sourcing Input
16 ______________________________________________________________________________________
Precision Transimpedance Logarithmic
Amplifier with Over 5 Decades of Dynamic Range
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
PACKAGE OUTLINE
12,16,20,24L QFN THIN, 4x4x0.8 mm
1
21-0139
B
2
PACKAGE OUTLINE
12,16,20,24L QFN THIN, 4x4x0.8 mm
2
21-0139
B
2
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implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 17
© 2003 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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