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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： | 15/18页 |
| 文件大小： | 490K |
| 代理商： | LOG102AIDR |
www.ti.com
LOG102
6
SBOS211B
14
I
1
I
2
1
10
8
11
3
12
7
4
5
6
V+
9
V–
10
F
Amplifier A
4 not being used.
C
10
F
LOG102
V
OUT
R
2
V
LOGOUT
V
OUT = G VLOGOUT
R
1
1000pF
Unused amplifiers should
have positive inputs grounded
and negative inputs tied to
their respective outputs.
FIGURE 1. Basic Connections with Output Gain Factor of the
LOG102.
APPLICATION INFORMATION
The LOG102 is a true logarithmic amplifier that uses the
base-emitter voltage relationship of bipolar transistors to
compute the logarithm, or logarithmic ratio, of a current ratio.
With two uncommitted on-chip operational amplifiers, the
LOG102 provides design flexibility and simplicity.
Figure 1 shows the basic connections required for operation
of the LOG102 with a gain factor. In order to reduce the
influence of lead inductance of power supply lines, it is
recommended that each supply be bypassed with a 10
F
tantalum capacitor in parallel with a 1000pF ceramic capaci-
tor, as shown in Figure 1. Connecting the capacitors as close
to the LOG102 as possible will contribute to noise reduction
as well.
INPUT CURRENT RANGE
To maintain specified accuracy, the input current range of the
LOG102 should be limited from 1nA to 1mA. Input currents
outside of this range may compromise LOG102 performance.
Input currents larger than 1mA result in increased nonlinearity.
An absolute maximum input current rating of 10mA is included
to prevent excessive power dissipation that may damage the
logging transistor.
On
±5V supplies the total input current (I
1 + I2) is limited to
1.1mA. Due to compliance issues internal to the LOG102, to
accommodate larger total input currents, supplies should be
increased.
Currents smaller than 1nA will result in increased errors due
the input bias currents of op amps A1 and A2 (typically 5pA).
The input bias currents may be compensated for, as shown in
Figure 2. The input stages of the amplifiers have FET inputs,
with input bias current doubling every 10
°C, which makes the
nulling technique shown practical only where the temperature
is fairly stable.
FIGURE 2. Bias Current Nulling.
V–
R
1'
> 1M
I
2
I
1
R
2'
10k
R
1
1M
R
2
10k
V+
14
1
9
10
5
V
OUT
6
V–
V+
C
LOG102
2N2905
I
REF
R
REF
2N2905
+15V
–15V
I
REF =
6V
R
REF
3.6k
6V
IN834
FIGURE 3. Temperature Compensated Current Source.
SETTING THE REFERENCE CURRENT
When the LOG102 is used to compute logarithms, either I1 or
I2 can be held constant and becomes the reference current to
which the other is compared.
VLOGOUT is expressed as:
VLOGOUT = (1V) log (I1/I2)
(1)
IREF can be derived from an external current source (such as
shown in Figure 3), or it may be derived from a voltage
source with one or more resistors. When a single resistor 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
1
+
R
2
R
1
+5V
R
3
V
REF = 100mV
R
3 >> R2
I
REF
–
V
OS
14
FIGURE 4. T Network for Reference Current.
A voltage divider may be used to reduce the value of the
resistor (as shown in Figure 4). When using this method, one
must consider the possible errors caused by the amplifier’s
input offset voltage. The input offset voltage of amplifier A1
has a maximum value of 1.5mV, making VREF a suggested
value of 100mV.
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参数描述 |
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| 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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| 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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