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参数资料
| 型号： | LOG102AIDR |
| 厂商： | TEXAS INSTRUMENTS INC |
| 元件分类： | 模拟运算功能 |
| 英文描述： | LOG OR ANTILOG AMPLIFIER, 1.4 MHz BAND WIDTH, PDSO14 |
| 封装： | GREEN, PLASTIC, MS-012AB, SOIC-14 |
| 文件页数： | 18/18页 |
| 文件大小： | 490K |
| 代理商： | LOG102AIDR |
www.ti.com
LOG102
9
SBOS211B
A
2
A
1
I
1
Q
1
Q
2
V
OUT = (1V) LOG
I
1
I
2
I
2
I
1
I
2
++
––
R
2
V
OUT
V
L
R
1
V
BE1
V
BE2
also
VV
RR
R
I
V
RR
R
nV
I
OUT
L
OUT
T
=
+
=
+
12
1
2
12
1
2
1
log
Using the base-emitter voltage relationship of matched
bipolar transistors, the LOG102 establishes a logarith-
mic function of input current ratios. Beginning with the
base-emitter voltage defined as
VV
I
where V
kT
q
BE
T
C
S
T
==
ln
:
k = Boltzmann’s constant = 1.381 10–23
T = Absolute temperature in degrees Kelvin
q = Electron charge = 1.602 10–19 Coulombs
IC = Collector current
IS = Reverse saturation current
From the circuit in Figure 11, we see that
VV
V
LBE
BE
=
12
–
Substituting (1) into (2) yields
VV
I
V
I
LT
S
T
S
=
1
2
ln
–
ln
If the transistors are matched and isothermal and
VTI = VT2, then (3) becomes:
VV
I
VV
I
and
ce
xx
Vn V
I
LT
SS
LT
=
=
1
12
1
2
10
1
2
23
ln
– ln
ln
sin
ln
. log
log
where n = 2.3
INSIDE THE LOG102
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(9)
(10)
(11)
FIGURE 11. Simplified Model of Log Amplifier.
(8)
or
It should be noted that the temperature dependance
associated with VT = kT/q is internally compensated on
the LOG102 by making R1 a temperature sensitive resis-
tor with the required positive temperature coefficient.
USING A LARGER REFERENCE VOLTAGE
REDUCES OFFSET ERRORS
Using a larger reference voltage to create the reference
current minimizes errors due to the LOG102’s input offset
voltage. Maintaining an increasing output voltage as a func-
tion of increasing photodiode current is also important in
many optical sensing applications. All zeros from the A/D
converter output represent zero or low scale photodiode
current. Inputting the reference current into I1, and designing
IREF such that it is as large or larger than the expected
maximum photodiode current is accomplished using this
requirement. The LOG102 configured with the reference
current connecting I1 and the photodiode current connecting
to I2 is shown in Figure 12. A3 is configured as a level shifter
with inverting gain and is used to scale the photodiode
current directly into the A/D input voltage range.
The wide dynamic range of the LOG102 is useful for measuring
avalanche photodiode current (APD) (see Figure 13).
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LOG102AIDRG4 | 功能描述:对数放大器 Logarithmic and Log Ratio Amp RoHS:否 制造商:Texas Instruments 通道数量:3 带宽:3 dB 共模抑制比（最小值）: 输入补偿电压:+/- 7 mV 输入电压范围（最大值）:5.5 V 工作电源电压:4.5 V to 5.5 V 电源电流:+/- 15 mA 工作温度范围:- 40 C to +85 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-16 封装:Reel |
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| LOG104AID | 功能描述:对数放大器 LOGARITHMIC AMP RoHS:否 制造商:Texas Instruments 通道数量:3 带宽:3 dB 共模抑制比（最小值）: 输入补偿电压:+/- 7 mV 输入电压范围（最大值）:5.5 V 工作电源电压:4.5 V to 5.5 V 电源电流:+/- 15 mA 工作温度范围:- 40 C to +85 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-16 封装:Reel |
| LOG104AID | 制造商:Texas Instruments 功能描述:IC AMP LOG SMD SOIC8 104 |
| LOG104AIDE4 | 功能描述:对数放大器 LOGARITHMIC AMP RoHS:否 制造商:Texas Instruments 通道数量:3 带宽:3 dB 共模抑制比（最小值）: 输入补偿电压:+/- 7 mV 输入电压范围（最大值）:5.5 V 工作电源电压:4.5 V to 5.5 V 电源电流:+/- 15 mA 工作温度范围:- 40 C to +85 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-16 封装:Reel |
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