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參數(shù)資料
| 型號(hào)： | MAX4207 |
| 廠商： | Maxim Integrated Products, Inc. |
| 元件分類： | 運(yùn)動(dòng)控制電子 |
| 英文描述： | Precision Transimpedance Logarithmic Amplifier with Over 5 Decades of Dynamic Range |
| 中文描述： | 高精度互阻對(duì)數(shù)放大器，動(dòng)態(tài)范圍大于105 |
| 文件頁數(shù)： | 12/15頁 |
| 文件大小： | 386K |
| 代理商： | MAX4207 |
M
Precision Transimpedance Logarithmic
Amplifier with Over 5 Decades of Dynamic Range
12
______________________________________________________________________________________
Output Offset
The inverting configuration utilized by the MAX4207
facilitates large output-offset voltage adjustments. The
magnitude of the offset voltage is given by the following
equation:
A resistive divider between REFVOUT, OSADJ, and
GND can be used to adjust V
OSADJ
(see Figure 5).
Scale Factor
The scale factor, K, is the slope of the logarithmic output.
For the LOGV1 amplifier, K = -0.25V/decade. Adjust the
overall scale factor for the MAX4207 using the uncom-
mitted LOGV2 amplifier and the following equation,
which refers to Figure 5:
Select R
2
between 1k
and 100k
.
Design Example
Desired:
Logarithmic intercept: 1μA
Overall scale factor = +1V/decade
Select R
1
= 10k
:
Photodiode Current Monitoring
Figure 6 shows the MAX4207 in an optical-power
measurement circuit, common in fiberoptic applications.
The MAX4007 current monitor converts the sensed APD
current to an output current that drives the MAX4207
LOGIIN input (APD current is scaled by 0.1). The
MAX4007 also buffers the high-voltage APD voltages
from the lower MAX4207 voltages. The MAX4207’s inter-
nal current reference sources 10nA (R
SET
= 5M
) to the
REFIIN input. This configuration sets the logarithmic inter-
cept 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.
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 MAX4207’s internal current reference driving
REFIIN. Alternatively, connect a photodiode to each of
the MAX4207’s logging inputs, LOGIIN and REFIIN, to
measure relative optical power (Figure 7).
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
MAX4207 outputs provide voltages proportional to the
log ratio of the two optical powers—an indicator of the
optical absorbance of the sample.
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 frequen-
cy. In this application, two bandpass optical filters with
overlapping “skirts” precede each photodiode. With
proper filter selection, the MAX4207 output can vary
monotonically (ideally linearly) with optical frequency.
R
k
V decade
1
0 25
.
k
2 10
40
×
=
/
R
V
μ
A
k
SET
=
=
0 5
.
10 1
50
R
R
K
.
2
1
0 25
=
V
V
R
R
R
OSADJ
REFOUT
=
+
4
3
4
V
V
R
R
OS
OSADJ
=
+
1
2
1
Table 1. MAX4207 Example Configurations
LOGV2 AMPLIFIER CONFIGURATION
INPUT CONDITIONS
I
LOG
> I
REF
(constant)
I
LOG
< I
REF
(constant)
I
LOG
> I
REF
(constant)
I
LOG
< I
REF
(constant)
V
LOGV1
Negative
Positive
Negative
Positive
V
LOGV2
Positive
Negative
Negative
Positive
Inverting
Noninverting
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MAX4207ETE | 功能描述:對(duì)數(shù)放大器 Transimpedance w/ 100Db Dynamic Range RoHS:否 制造商:Texas Instruments 通道數(shù)量:3 帶寬:3 dB 共模抑制比（最小值）: 輸入補(bǔ)償電壓:+/- 7 mV 輸入電壓范圍（最大值）:5.5 V 工作電源電壓:4.5 V to 5.5 V 電源電流:+/- 15 mA 工作溫度范圍:- 40 C to +85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-16 封裝:Reel |
| MAX4207ETE+ | 功能描述:對(duì)數(shù)放大器 Transimpedance w/ 100Db Dynamic Range RoHS:否 制造商:Texas Instruments 通道數(shù)量:3 帶寬:3 dB 共模抑制比（最小值）: 輸入補(bǔ)償電壓:+/- 7 mV 輸入電壓范圍（最大值）:5.5 V 工作電源電壓:4.5 V to 5.5 V 電源電流:+/- 15 mA 工作溫度范圍:- 40 C to +85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-16 封裝:Reel |
| MAX4207ETE+T | 功能描述:對(duì)數(shù)放大器 Transimpedance w/ 100Db Dynamic Range RoHS:否 制造商:Texas Instruments 通道數(shù)量:3 帶寬:3 dB 共模抑制比（最小值）: 輸入補(bǔ)償電壓:+/- 7 mV 輸入電壓范圍（最大值）:5.5 V 工作電源電壓:4.5 V to 5.5 V 電源電流:+/- 15 mA 工作溫度范圍:- 40 C to +85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-16 封裝:Reel |
| MAX4207ETE-T | 功能描述:對(duì)數(shù)放大器 Transimpedance w/ 100Db Dynamic Range RoHS:否 制造商:Texas Instruments 通道數(shù)量:3 帶寬:3 dB 共模抑制比（最小值）: 輸入補(bǔ)償電壓:+/- 7 mV 輸入電壓范圍（最大值）:5.5 V 工作電源電壓:4.5 V to 5.5 V 電源電流:+/- 15 mA 工作溫度范圍:- 40 C to +85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-16 封裝:Reel |
| MAX4208AUA+ | 功能描述:儀表放大器 Low Offset/Drift Instrumentation Amp RoHS:否 制造商:Texas Instruments 通道數(shù)量: 輸入補(bǔ)償電壓:150 V 可用增益調(diào)整: 最大輸入電阻:10 kOhms 共模抑制比（最小值）:88 dB 工作電源電壓:2.7 V to 36 V 電源電流:200 uA 最大工作溫度:+ 125 C 最小工作溫度:- 40 C 封裝 / 箱體:MSOP-8 封裝:Bulk |
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