MAX4206
Precision Transimpedance Logarithmic
Amplifier with Over 5 Decades of Dynamic Range
_______________________________________________________________________________________ 9
SMALL-SIGNAL AC RESPONSE
I
LOG
TO V
LOGV1
MAX4206 toc27
FREQUENCY (Hz)
NORMALIZED GAIN (dB)
1M100k10k1k
-50
-40
-30
-20
-10
0
10
-60
100 10M
I
LOG
= 100
µ
A
I
LOG
= 1mA
I
LOG
= 10
µ
A
I
LOG
= 1
µ
A
I
LOG
= 100nA
C
COMP
= 33pF
R
COMP
= 330
Ω
SMALL-SIGNAL AC RESPONSE
I
LOG
TO V
LOGV1
MAX4206 toc28
FREQUENCY (Hz)
NORMALIZED GAIN (dB)
1M100k10k1k
-50
-40
-30
-20
-10
0
10
-60
100 10M
I
LOG
= 100
µ
A
I
LOG
= 1mA
I
LOG
= 10
µ
A
I
LOG
= 1
µ
A
I
LOG
= 100nA
C
COMP
= 100pF
R
COMP
= 1k
Ω
SMALL-SIGNAL AC RESPONSE
OF BUFFER
MAX4206 toc29
FREQUENCY (Hz)
NORMALIZED GAIN (dB)
10M1M100k
-9
-6
-3
0
3
-12
10k 100M
A
V
= 2V/V
A
V
= 4V/V
A
V
= 1V/V
Typical Operating Characteristics (continued)
(V
CC
= +5V, V
EE
= GND = 0V, I
REF
= 1µA, I
LOG
= 10µA, LOGV2 = SCALE, LOGV1 = OSADJ, CMVIN = CMVOUT, R
SET
> 1MΩ,
T
A
= +25°C, unless otherwise noted.)
Pin Description
PIN NAME FUNCTION
1, 9 N.C. No Connection. Not internally connected.
2
REFVOUT
1.238V Reference Voltage Output. Bypass REFVOUT to GND with a 0 to 1µF capacitor (optional).
3 GND Ground
4V
EE
Negative Power Supply. Bypass V
EE
to GND with a 0.1µF capacitor.
5 LOGV1 Logarithmic Amplifier Voltage Output 1. The output scale factor of LOGV1 is 0.25V/decade.
6 OSADJ
Offset Adjust Input. When operating from a single power supply, current applied to OSADJ adjusts
the output offset voltage (see the Output Offset section).
7 SCALE
Scale Factor Input. Adjust the output scale factor for LOGV2 using a resistive divider (see the Scale
Factor section).
8 LOGV2
Logarithmic Amplifier Voltage Output 2. Adjust the output scale factor for LOGV2 using a resistive
divider (see the Scale Factor section).
10 V
CC
Positive Power Supply. Bypass V
CC
to GND with a 0.1µF capacitor.
11 REFISET
Current Reference Adjust Input. A resistor (R
SET
), from REFISET to GND, adjusts the current at
REFIOUT (see the Adjusting the Logarithmic Intercept section).
12
CMVOUT
0.5V Common-Mode Voltage Reference Output. Bypass CMVOUT to GND with a 0.1µF capacitor.
13
REFIOUT
Current Reference Output. The internal current reference output is available at REFIOUT.
14 REFIIN
Current Reference Input. Apply an external reference current at REFIIN. I
REFIIN
is the reference
current used by the logarithmic amplifier when generating LOGV1.
15 LOGIIN
Current Input to Logarithmic Amplifier. LOGIIN is typically connected to a photodiode anode or other
external current source.
16 CMVIN
Common-Mode Voltage Input. V
CMVIN
is the common-mode voltage for the input and reference
amplifiers (see the Common Mode section).
