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參數(shù)資料
| 型號： | LOG100JP |
| 廠商： | TEXAS INSTRUMENTS INC |
| 元件分類： | 模擬運算功能 |
| 英文描述： | LOG OR ANTILOG AMPLIFIER, 0.045 MHz BAND WIDTH, CDIP14 |
| 封裝： | HERMETIC SEALED, CERAMIC, DIP-14 |
| 文件頁數(shù)： | 8/11頁 |
| 文件大小： | 112K |
| 代理商： | LOG100JP |
LOG100
6
Log conformity is defined as the peak deviation from the
best-fit straight line of the V
OUT versus log (I1/I2) curve. This
is expressed as a percent of peak-to-peak full scale output.
Thus, the nonlinearity error expressed in volts over m
decades is
V
OUT (NONLIN) = K 2Nm V
(12)
where N is the log conformity error, in percent.
INDIVIDUAL ERROR COMPONENTS
The ideal transfer function with current input is
V
OUT = K Log
(13)
The actual transfer function with the major components of
error is
V
OUT = K (1 ± K) log
±K 2Nm ± V
OS OUT
(14)
The individual component of error is
K = scale factor error (0.3%, typ)
I
B1 = bias current of A1 (1pA, typ)
I
B2 = bias current of A2 (1pA, typ)
N = log conformity error ( 0.05%, 0.1%, typ)
V
OS OUT = output offset voltage (1mV, typ)
m = number of decades over which N is specified:
0.05% for m = 5, 0.1% for m = 6
Example: what is the error with K = 3 when
I
1 = 1A and I2 = 100nA
V
OUT = 3(1 ± 0.003) log
±3(2)(0.0005)5±1mV
(15)
≈ 3.009 log
+ 0.015 + 0.001
(16)
= 3.009 (1) + 0.015 + 0.001
(17)
= 3.025V
(18)
Since the ideal output is 3.000V, the error as a percent of
reading is
% error =
x 100% = 0.83%
(19)
For the case of voltage inputs, the actual transfer function is
V
OUT = K(1 ± K) log
±K 2Nm ±V
OS OUT
(20)
FREQUENCY RESPONSE
The 3dB frequency response of the LOG100 is a function of
the magnitude of the input current levels and of the value of
the frequency compensation capacitor. See Typical Perfor-
mance Curves for details.
TOTAL ERROR
The total error is the deviation (expressed in mV) of the
actual output from the ideal output of V
OUT = K log (I1/I2).
Thus,
V
OUT (ACTUAL) = VOUT (IDEAL) ± Total Error.
It represents the sum of all the individual components of
error normally associated with the log amp when operated in
the current input mode. The worst-case error for any given
ratio of I
1/I2 is the largest of the two errors when I1 and I2 are
considered separately.
Example:
I
1 varies over a range of 10nA to 1A and I2 varies from
100nA to 10
A. What is the maximum error?
Table I shows the maximum errors for each decade combi-
nation of I
1 and I2.
Since the largest value of I
1/I2 is 10 and the smallest is 0.001,
K is set at 3V per decade so the output will range from +3V
to –9V. The maximum total error occurs when I
1 = 10nA and
is equal to K x 30mV. This represents a 0.75% of peak-to-
peak FSO error 3 x 0.030/12 x 100% = 0.75% where the full
scale output is 12V (from +3V to –9V).
ERRORS RTO AND RTI
As with any transfer function, errors generated by the
function itself may be Referred-to-Output (RTO) or Re-
ferred-to-Input (RTI). In this respect, log amps have a
unique property:
Given some error voltage at the log amp’s output, that
error corresponds to a constant percent of the input
regardless of the actual input level.
Refer to: Yu Jen Wong and William E. Ott, “Function
Circuits: Design & Applications”, McGraw-Hill Book, 1976.
LOG CONFORMITY
Log conformity corresponds to linearity when V
OUT is plot-
ted versus I
1/I2 on a semilog scale. In many applications, log
conformity is the most important specification. This is true
because bias current errors are negligible (1pA compared to
input currents of 1nA and above) and the scale factor and
offset errors may be trimmed to zero or removed by system
calibration. This leaves log conformity as the major source
of error.
I
2
I
1
I
1 – IB1
I
2 – IB2
TABLE I. I
1/I2 and Maximum Errors.
I
1 (maximum error)
(1)
I 2
(maximum
error)
(1)
NOTE: (1) Maximum errors are in parenthesis.
10nA
100nA
1
A
(30mV)
(25mV)
(20mV)
100nA
0.1
1
10
(25mV)
(30mV)
(25mV)
1
A
0.01
0.1
1
(20mV)
(30mV)
(25mV)
(20mV)
10
A
0.001
0.01
0.1
(25mV)
(30mV)
(25mV)
10–7 –10–12
10–6 –10–12
10–7
10–6
R
1
– I
B1 ±
R
1
V
1
R
2
– I
B2 ±
R
2
V
2
E
OS1
E
OS2
3
0.025
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LOG100JP-2 | 制造商:Rochester Electronics LLC 功能描述:LOGARITHMIC AMPLIFIER - Bulk |
| LOG100JP-3 | 制造商:Rochester Electronics LLC 功能描述:LOG & LOG RATIO - Bulk |
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| LOG101 | 制造商:BB 制造商全稱:BB 功能描述:Precision LOGARITHMIC AND LOG RATIO AMPLIFIER |
| LOG101AID | 功能描述:對數(shù)放大器 LOGARITHMIC AMP RoHS:否 制造商:Texas Instruments 通道數(shù)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 |
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