MAX4207ETE+T Maxim Integrated Products, MAX4207ETE+T Datasheet - Page 9

• Manufacturer Part Number: MAX4207ETE+T
• Description: IC AMP TRANS LOG 16-TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX4207ETE+T

• Amplifier Type: Logarithmic
• Number Of Circuits: 1
• Slew Rate: 12 V/µs
• Gain Bandwidth Product: 5MHz
• -3db Bandwidth: 1MHz
• Current - Input Bias: 10pA
• Voltage - Input Offset: 600µV
• Current - Supply: 5mA
• Current - Output / Channel: 58mA
• Voltage - Supply, Single/dual (±): 2.7 V ~ 11 V, ±2.7 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-TQFN Exposed Pad
• Number Of Channels: 1
• Input Offset Voltage: 2 mV
• Supply Current: 6 mA
• Operating Temperature Range: + 85 C
• Mounting Style: SMD/SMT
• Power Dissipation: 1349 mW
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Output Type: -
• Lead Free Status / Rohs Status: Details

Figure 2. Simplified Model of a Logarithmic Amplifier
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:
where:
The logarithmic amplifier compares V
ence voltage V
known reference current, I
dencies of a logarithmic amplifier relate to the thermal
voltage, (kT/q), and I
the I
following manner:
Amplifier with Over 5 Decades of Dynamic Range
V
k = 1.381 x 10
T = absolute temperature (K)
q = 1.602 x 10
I
I
C
S
BE
S
LOGIIN
CMVIN
REFIIN
= reverse saturation current
= collector current
temperature dependence of the amplifier in the
= base-emitter voltage of a bipolar transistor
I
I
REF
LOG
BE2
-23
V
–19
_______________________________________________________________________________________
, which is a logarithmic voltage for a
BE
J/K
C
S
=
Detailed Description
. Matched transistors eliminate
Precision Transimpedance Logarithmic



V
V
V
V
kT
CC
EE
CC
EE
q
REF



. The temperature depen-
ln



I
I
C
S



BE1
to the refer-
V
V
BE1
BE2
Theory
where:
k = scale factor (V/decade)
I
I
The MAX4207 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.
The ideal logarithmic amplifier transfer function is:
Adjust K (see the Scale Factor section) to increase the
transfer-function slope as illustrated in Figure 3. Adjust
I
Intercept section) to shift the logarithmic intercept to
the left or right as illustrated in Figure 4.
Log conformity is the maximum deviation of the
MAX4207’s output from the best-fit straight line of the
V
a percent of the full-scale output or an output voltage.
The log nature of the MAX4207 insures that any addi-
tive error at LOGV1 corresponds to multiplicative error
at the input, regardless of input level.
LOG
REF
REF
LOGV1
Referred-to-Input and Referred-to-Output Errors
= the reference current at REFIIN
using REFISET (see the Adjusting the Logarithmic
= the input current at LOGIIN
versus log (I
V
=
=
=
=
= ×
OUT
K












kT
kT
kT
kT
q
q
q
q
V
log
IDEAL












=
(








ln
V
ln
ln
ln( ) log
10
BE













10
I
LOG
I



1
I
I
LOG
LOG
REF
LOG
I
=
I
I
−
S
LOG
I
REF
S
)
K
V




BE
/I

 −



 

 −

×
REF







2
10
log
ln



) curve. It is expressed as






kT
q
I
10
I
I
LOG
REF
REF
I



S



ln
I
I
LOG
REF









Transfer Function








I
REF
I
Log Conformity
S



(see Figure 3)



Definitions




9