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參數資料
| 型號： | LOG114AIRGVRG4 |
| 元件分類： | 對數放大器 |
| 英文描述： | Single-Supply, High-Speed, Precision LOGARITHMIC AMPLIFIER |
| 中文描述： | 單電源，高速，精密對數放大器 |
| 文件頁數： | 21/30頁 |
| 文件大?。?/td> | 616K |
| 代理商： | LOG114AIRGVRG4 |
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"#$$%
SBOS301A MAY 2004 REVISED MARCH 2007
www.ti.com
21
INSIDE THE LOG114
The LOG114 uses two matched logarithmic amplifiers
(A
1
and A
2
with logging diodes in the feedback loops) to
generate the outputs log (I
1
) and log (I
2
), respectively.
The gain of 6.25 differential amplifier (A
3
) subtracts the
output of A
2
from the output of A
1
, resulting in [log (I
1
)
log (I
2
)], or log (I
1
/I
2
). The symmetrical design of the
A
1
and A
2
logarithmic amps allows I
1
and I
2
to be used
interchangeably, and provides good bandwidth and
phase characteristics with frequency.
DEFINITION OF TERMS
Transfer Function
The ideal transfer function of the LOG114 is:
V
LOGOUT
0.375
log
I
1
1
2
This transfer function can be seen graphically in the typ-
ical characteristic curve,
V
LOGOUT
vs I
REF
.
When a pedestal, or offset, voltage (V
Com
)
is connected
to the Com pin, an additional offset term is introduced
into the equation:
V
LOGOUT
0.375
log
I
1
1
2
V
Com
Accuracy
Accuracy considerations for a log ratio amplifier are
somewhat more complicated than for other amplifiers.
This complexity exists because the transfer function is
nonlinear and has two inputs, each of which can vary
over
a
dynamic range. The accuracy for any combination of
inputs is determined from the total error specification.
wide
Total Error
The total error is the deviation of the actual output from
the ideal output. Thus,
V
LOGOUT(ACTUAL)
= V
LOGOUT(IDEAL)
±
Total Error
It represents the sum of all the individual components
of error normally associated with the log amp when op-
erating in the current input mode. The worst-case error
for any given ratio of I
1
/I
2
is the largest of the two errors
when I
1
and I
2
are considered separately. Temperature
can also affect total error.
Errors RTO and RTI
As with any transfer function, errors generated by the
function 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 out-
put, that error corresponds to a constant percent of the
input, regardless of the actual input level.
Log Conformity
For the LOG114, log conformity is calculated in the
same way as linearity and is plotted as I
1
/I
2
on a semi-
log scale. In many applications, log conformity is the
most important specification. This condition is true be-
cause bias current errors are negligible (5pA for the
LOG114), and the scale factor and offset errors may be
trimmed to zero or removed by system calibration.
These factors leave log conformity as the major source
of error.
Log conformity is defined as the peak deviation from the
best fit straight line of the V
LOGOUT
versus log (I
1
/I
2
)
curve. Log conformity is then expressed as a percent of
ideal fullscale output. Thus, the nonlinearity error ex-
pressed in volts over
m
decades is:
V
LOGOUT (NONLIN)
= 0.375V/decade
2Nm
where N is the log conformity error, in percent.
INDIVIDUAL ERROR COMPONENTS
The ideal transfer function with current input is:
V
LOGOUT IDEAL
0.375
log
I
1
1
2
The actual transfer function with the major components
of error is:
0.375(1
K)
log
I
1
I
2
2Nm
V
OSO
where:
K = gain error (0.4%, typ, as specified in the
Electri-
cal Characteristics
table)
I
B1
= bias current of A
1
(5pA, typ)
I
B2
= bias current of A
2
(5pA, typ)
m = number of decades over which the log
conformity error is specified
N = log conformity error (0.1%, typ for m = 5 decades;
0.9% typ for m = 7.5 decades)
V
OSO
= output offset voltage (11mV, typ for
±
5V sup-
plies; 14mV, typ for +5V supplies)
To determine the typical error resulting from these error
components, first compute the ideal output. Then calcu-
late the output again, this time including the individual
error components. Then determine the error in percent
using Equation (21):
%error
V
LOGOUT IDEAL
V
LOGOUT TYP
V
LOGOUTIDEAL
100%
(17)
(18)
(19)
(20)
(21)
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相關代理商/技術參數 |
參數描述 |
|---|---|
| LOG114AIRGVT | 功能描述:對數放大器 Precision High-Speed RoHS:否 制造商:Texas Instruments 通道數量:3 帶寬:3 dB 共模抑制比（最小值）: 輸入補償電壓:+/- 7 mV 輸入電壓范圍（最大值）:5.5 V 工作電源電壓:4.5 V to 5.5 V 電源電流:+/- 15 mA 工作溫度范圍:- 40 C to +85 C 安裝風格:SMD/SMT 封裝 / 箱體:VQFN-16 封裝:Reel |
| LOG114AIRGVTG4 | 功能描述:對數放大器 Prec High-Speed Logarithmic Amp RoHS:否 制造商:Texas Instruments 通道數量:3 帶寬:3 dB 共模抑制比（最小值）: 輸入補償電壓:+/- 7 mV 輸入電壓范圍（最大值）:5.5 V 工作電源電壓:4.5 V to 5.5 V 電源電流:+/- 15 mA 工作溫度范圍:- 40 C to +85 C 安裝風格:SMD/SMT 封裝 / 箱體:VQFN-16 封裝:Reel |
| LOG114EVM | 功能描述:放大器 IC 開發(fā)工具 LOG114 Eval Mod RoHS:否 制造商:International Rectifier 產品:Demonstration Boards 類型:Power Amplifiers 工具用于評估:IR4302 工作電源電壓:13 V to 23 V |
| LOG1527 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:由CMOS工藝設計制造的可內燒的學習碼編碼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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