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参数资料
| 型号： | LOG101 |
| 英文描述： | Precision LOGARITHMIC AND LOG RATIO AMPLIFIER |
| 中文描述： | 精密对数和对数比率放大器 |
| 文件页数： | 13/13页 |
| 文件大小： | 281K |
| 代理商： | LOG101 |
www.ti.com
LOG101
9
SBOS242B
TOTAL ERROR
The total error is the deviation (expressed in mV) of the
actual output from the ideal output of VOUT = 1V log (I1/I2).
Thus,
VOUT(ACTUAL) = VOUT(IDEAL) ± Total Error.
It represents the sum of all the individual components of error
normally associated with the log amp when operated in the
current input mode. The worst-case error for any given ratio
of I1/I2 is the largest of the two errors when I1 and I2 are
considered separately. Temperature can affect total error.
ERRORS RTO AND RTI
As with any transfer function, errors generated by the func-
tion itself may be Referred-to-Output (RTO) or Referred-to-
Input (RTI). In this respect, log amps have a unique property:
Given some error voltage at the log amp’s output, that error
corresponds to a constant percent of the input regardless of
the actual input level.
USING A LARGER REFERENCE VOLTAGE
REDUCES OFFSET ERRORS
Using a larger reference voltage to create the reference
current minimizes errors due to the LOG101’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 LOG101 configured with the reference
current connecting I1 and the photodiode current connecting
A
1
A
2
LOG101
Q
1
Q
2
OPA703
R
2
R
3
R
2
6
R
3
C
V
OUT
V
REF
I
REF
I
REF =
I
MIN to IMAX
V
REF
R
1
V
OUT = VREF –
(1V)LOG
(
)
R
2
R
3
I
REF
I
PHOTO
I
1
I
2
8
1
I
PHOTO
A/D
Converter
R
1
V
MIN to VMAX
3
FIGURE 13. Technique for Using Full-Scale Reference Current Such that VOUT Increases with Increasing Photodiode Current.
to I2 is shown in Figure 13. The OPA703 is configured as a
level shifter with inverting gain and is used to scale the
photodiode current directly into the A/D converter input
voltage range.
The wide dynamic range of the LOG101 is also useful for
measuring avalanche photodiode current (APD) (see Figure 14).
LOG CONFORMITY
For the LOG101, log conformity is calculated the same as
linearity and is plotted I1/I2 on a semi-log scale. In many
applications, log conformity is the most important specifica-
tion. This is because bias current errors are negligible
(5pA compared to input currents of 100pA and above) and
the scale factor and offset errors may be trimmed to zero or
removed by system calibration. This leaves log conformity as
the major source of error.
Log conformity is defined as the peak deviation from the best
fit straight line of the VOUT versus log (I1/I2) curve. This is
expressed as a percent of ideal full-scale output. Thus, the
nonlinearity error expressed in volts over m decades is:
VOUT(NONLIN) = 1V/dec 2NmV
where N is the log conformity error, in percent.
INDIVIDUAL ERROR COMPONENTS
The ideal transfer function with current input is:
VV
I
OUT =
( )
1
2
log
The actual transfer function with the major components of
error is:
VV
K
II
Nm
V
OUT
B
OS O
=
( ) ±
(
)
±±
11
2
11
22
log
–
(6)
(7)
(8)
(9)
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LOG101AID | 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 |
| LOG101AIDE4 | 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 |
| LOG101AIDR | 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 |
| LOG101AIDRE4 | 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 |
| LOG102 | 制造商:TI 制造商全称:Texas Instruments 功能描述:LOGARITHMIC AND LOG RATIO AMPLIFIER |
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