參數(shù)資料
型號(hào)： LOG114AIRGVT
元件分類： 對(duì)數(shù)放大器
英文描述： Single-Supply, High-Speed, Precision LOGARITHMIC AMPLIFIER
中文描述： 單電源，高速，精密對(duì)數(shù)放大器
文件頁(yè)數(shù)： 11/30頁(yè)
文件大?。?/td> 616K
代理商： LOG114AIRGVT
"#$$%
SBOS301A MAY 2004 REVISED MARCH 2007
www.ti.com
11
APPLICATIONS INFORMATION
OVERVIEW
The LOG114 is a precision logarithmic amplifier that is
capable of measuring currents over a dynamic range of
eight decades. It computes the logarithm, or log ratio,
of an input current relative to a reference current ac-
cording to equation (1).
V
LOGOUT
0.375
log
10
I
1
I
2
The output at V
LOGOUT
can be digitized directly, or scaled
for an ADC input using an uncommitted or external op
amp.
An offsetting voltage (V
Com
) can be connected to the
Com pin to raise the voltage at V
LOGOUT
. When an
offsetting voltage is used, the transfer function
becomes:
V
LOGOUT
0.375
log
10
I
1
I
2
V
Com
Either I
1
or I
2
can be held constant to serve as the refer-
ence current, with the other input being used for the in-
put signal. The value of the reference current is selected
such that the output at V
LOGOUT
(pin 9) is zero when the
reference current and input current are equal. An on-
chip 2.5V reference is provided for use in generating the
reference current.
Two additional amplifiers, A
4
and A
5
, are included in the
LOG114 for use in scaling, offsetting, filtering, threshold
detection, or other functions.
BASIC CONNECTIONS
Figure 1 and Figure 2 show the LOG114 in typical dual
and single-supply configurations, respectively. To re-
duce the influence of lead inductance of power-supply
lines, it is recommended that each supply be bypassed
with a 10
μ
F tantalum capacitor in parallel with a 1000pF
ceramic capacitor as shown in Figure 1 and Figure 2.
Connecting these capacitors as close to the LOG114
V+ supply pin to ground as possible improves supply
related noise rejection.
Q
1
R
1
R
2
R
5
100k
R
6
66.5k
R
7
100k
R
8
56.2k
R
3
R
2.5M
R
4
V
O4(2)
IN
4
+IN
4
V
LOGOUT(1)
+IN
5
IN
5
14
V
O5
V
CMIN
I
1
4
11
10
9
5
3
15
13
12
16 V
REF
2.5V
REF
V
6
Com
V
REF GND
Q
2
A
3
A
1
A
2
A
4
A
5
I
REF
1
F
Input Signal
100pAto10mA
I
2
V+
8
1
7
+5V
+
+
5V
1000pF
1000pF
10
μ
F
10
μ
F
LOG114
NOTE: (1) V
LOGOUT
= 0.375
×
log(I
/I
)
(2) V
O4
0.249
×
log(I
1
/I
2
) + 1.5V
Figure 1. Dual Supply Configuration Example for Best Accuracy Over Eight Decades.
(1)
(2)
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LOG1527 制造商:未知廠家 制造商全稱:未知廠家 功能描述:由CMOS工藝設(shè)計(jì)制造的可內(nèi)燒的學(xué)習(xí)碼編碼IC.
LOG2112 制造商:TI 制造商全稱:Texas Instruments 功能描述:LOGARITHMIC AND LOG RATIO AMPLIFIERS
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