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參數(shù)資料
| 型號(hào)： | AN-242 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | LJT 18C 18#20 SKT RECP |
| 中文描述： | 應(yīng)用新的精密運(yùn)算放大器 |
| 文件頁數(shù)： | 4/16頁 |
| 文件大?。?/td> | 267K |
| 代理商： | AN-242 |
Bias current compensation is more difficult for non-inverting
amplifiers because the common-mode voltage varies. With
a voltage follower, everything can be bootstrapped to the
output and powered by a regulated current source, as
shown in Figure 6. The LM334 is a temperature sensor. It
regulates against voltage changes and its output varies lin-
early with temperature, so it fits the bill.
Although the LM334 can accommodate voltage changes
fast enough to work with the LM11, it is not fast enough for
the high-speed circuits to be described. But compensation
can still be obtained by using the zener diode pre-regulator
bootstrapped to the output and powered by either a resistor
or FET current source. The LM385 fits well here because
both the breakdown voltage and minimum operating current
are low.
With ordinary op amps, the collector base voltage of the
input transistors varies with the common-mode voltage. A
50% change in bias current over the common-mode range
is not unusual, so compensating the bias current of a follow-
er has limited value. However, the bootstrapped input stage
of the LM11 reduces this to about 2 pA for a
g
20V com-
mon-mode swing, giving a 2
c
10
13
X
common-mode input
resistance.
fast amplifiers
A precision DC amplifier, although slow, can be used to sta-
bilize the offset voltage of a less precise fast amplifier. As
shown in Figure 7, the slow amplifier senses the voltage
across the input terminals and supplies a correction signal
to the balance terminals of the fast amplifier. The LM11 is
particularly interesting in this respect as it does not degrade
the input bias current of the composite even when the fast
amplifier has a FET input.
Surprisingly, with the LM11, this will work for both inverting
and non-inverting connections because its common-mode
slew recovery is a lot faster than that of the main loop. This
was accomplished, even with circuitry running under
100 nA, by proper clamping and by bootstrapping of internal
stray capacitances.
TL/H/7479–7
Figure 6. This circuit shows how bias current compen-
sation can be used on a voltage follower.
TL/H/7479–8
Figure 7. A slow amplifier can be used to null the offset
of a fast amplifier.
4
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| AN-40 | Application Note 40 |
| AN-5002 | LJT 18C 18#20 SKT WALL RECP |
| AN-5025 | Applications Using the GTLP10B320 |
| AN-5026 | Circular Connector; No. of Contacts:19; Series:MS27656; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:15; Circular Contact Gender:Pin; Circular Shell Style:Wall Mount Receptacle; Insert Arrangement:15-19 RoHS Compliant: No |
| AN-5031 | GTLP Power Configuration |
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