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| 型号： | LOG114AIRGVR |
| 厂商： | TEXAS INSTRUMENTS INC |
| 元件分类： | 模拟运算功能 |
| 英文描述： | LOG OR ANTILOG AMPLIFIER, PQCC16 |
| 封装： | 4 X 4 MM, GREEN, PLASTIC, QFN-16 |
| 文件页数： | 8/29页 |
| 文件大小： | 637K |
| 代理商： | LOG114AIRGVR |
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LOG114
SBOS301A MAY 2004 REVISED MARCH 2007
www.ti.com
16
SETTING THE REFERENCE CURRENT
When the LOG114 is used to compute logarithms, ei-
ther I1 or I2 can be held constant to become the refer-
ence current to which the other is compared.
If IREF is set to the lowest current in the span of the signal
current (as shown in the front page figure), VLOGOUT will
range from:
V
LOGOUT + 0.375
log
10
I
1 min
I
1 max signal
^ 0V
to some maximum value:
V
LOGOUT + 0.375
log
10
I
1 min
I
1 max signal
While convenient, this approach does not usually result
in best performance, because I1 min accuracy is difficult
to achieve, particularly if it is < 20nA.
A better way to achieve higher accuracy is to choose
IREF to be in the center of the full signal range. For
example, for a signal range of 1nA to 1mA, it is better
to use this approach:
I
REF
+ I
SIGNAL min
1mA 1nA
+ 1mAdc
than it is to set IREF = 1nA. It is much easier and more
precise (that is, dc accuracy, temperature stability, and
lower noise) to establish a 1mA dc current level than a
1nA level for the reference current.
The reference current may be derived from a voltage
source with one or more resistors. When a single resis-
tor is used, the value may be large depending on IREF.
If IREF is 10nA and +2.5V is used:
RREF = 2.5V/10nA = 250M
A voltage divider may be used to reduce the value of the
resistor, as shown in Figure 5. When using this method,
one must consider the possible errors caused by the
amplifier input offset voltage. The input offset voltage of
amplifier A1 has a maximum value of 4mV in a ±5V sup-
ply system, and a maximum value of 7mV in a +5V sup-
ply system. Resistor temperature stability and noise
contributions should also be considered.
A
1
+
R
2
R
1
+5V
R
3
V
REF =100mV
R
3 >> R2
I
REF
V
OS
1
Figure 5. T-Network for Reference Current.
VREF may be an external precision voltage reference, or
the on-chip 2.5V voltage reference of the LOG114.
IREF can be derived from an external current source,
such as that shown in Figure 6.
2N2905
I
REF
R
REF
2N2905
+15V
15V
I
REF =
6V
R
REF
3.6k
6V
IN834
Figure 6. Temperature-Compensated Current Source.
(14)
(15)
(16)
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LOG114AIRGVRG4 | 功能描述:对数放大器 Prec High-Speed 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 |
| LOG114AIRGVT | 功能描述:对数放大器 Precision High-Speed 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 |
| LOG114AIRGVTG4 | 功能描述:对数放大器 Prec High-Speed 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 |
| LOG114EVM | 功能描述:放大器 IC 开发工具 LOG114 Eval Mod RoHS:否 制造商:International Rectifier 产品:Demonstration Boards 类型:Power Amplifiers 工具用于评估:IR4302 工作电源电压:13 V to 23 V |
| LOG1527 | 制造商:未知厂家 制造商全称:未知厂家 功能描述:由CMOS工艺设计制造的可内烧的学习码编码IC. |
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