參數(shù)資料
型號(hào): LOG104AIDR
廠商: TEXAS INSTRUMENTS INC
元件分類: 模擬運(yùn)算功能
英文描述: LOG OR ANTILOG AMPLIFIER, 0.01 MHz BAND WIDTH, PDSO8
封裝: ROHS COMPLIANT, PLASTIC, MS-012AA, SOIC-8
文件頁(yè)數(shù): 10/14頁(yè)
文件大小: 294K
代理商: LOG104AIDR
www.ti.com
LOG104
5
SBOS243C
TYPICAL CHARACTERISTICS (Cont.)
At TA = +25°C, VS = ±5V, RL = 10k, unless otherwise noted.
17
15
13
11
9
7
5
3
1
–1
Input Current (I
1 or I2)
Log
Conformity
(mV)
LOG CONFORMITY vs INPUT CURRENT
+85
°C
+75
°C
–40
°C to +25°C
100pA
1nA
10nA
100nA
1
A10A 100A1mA
LOG CONFORMITY vs TEMPERATURE
Log
Conformity
(m%)
350
300
250
200
150
100
50
0
–40 –30 –20 –10 0
10 20
30 4050 6070 8090
Temperature (
°C)
7 Decades
(100pA to 1mA)
6 Decades
(1nA to 1mA)
5 Decades
(1nA to 100
A)
8
1
6
3
4
5
V–
V+
10
F
LOG104
1000pF
10
F
1000pF
I
1
I
2
V
OUT
C
FIGURE 1. Basic Connections of the LOG104.
APPLICATION INFORMATION
The LOG104 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.
Figure 1 shows the basic connections required for operation
of the LOG104. 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 capacitor, as shown in
Figure 1. Connecting the capacitors as close to the LOG104
as possible will contribute to noise reduction as well.
INPUT CURRENT RANGE
To maintain specified accuracy, the input current range of the
LOG104 should be limited from 100pA to 3.5mA. Input currents
outside of this range may compromise LOG104 performance.
Input currents larger than 3.5mA 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
4.5mA. Due to compliance issues internal to the LOG104, to
accommodate larger total input currents, supplies should be
increased.
Currents smaller than 100pA 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+
8
1
4
6
3
V
OUT
5
V–
V+
C
LOG104
GND
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