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| 型號： | LB-9 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Universal Balancing Techniques |
| 中文描述： | 通用平衡技術(shù) |
| 文件頁數(shù)： | 1/3頁 |
| 文件大?。?/td> | 73K |
| 代理商： | LB-9 |
Universal Balancing
Techniques
IC op amps are widely accepted as a universal analog
component. Although the circuit designs may vary, most
devices are functionally interchangeable. However, offset
voltage balancing remains a personality trait of the particular
amplifier design. The techniques shown here allow offset
voltage balancing without regard to the internal circuitry of
the amplifier.
The circuit shown in
Figure 1
is used to balance out the
offset voltage of inverting amplifiers having a source resis-
tance of 10 k
or less. A small current is injected into the
summing node of the amplifier through R
1
. Since R
1
is 2000
times as large as the source resistance the voltage at the
arm of the pot is attenuated by a factor of 2000 at the
summing node. With the values given and
±
15V supplies the
output may be zeroed for offset voltages up to
±
7.5 mW.
If the value of the source resistance is much larger than 10
k
, the resistance needed for R
1
becomes too large. In this
case it is much easier to balance out the offset by supplying
a small voltage at the non-inverting input of the amplifier.
Figure 2
shows such a scheme. Resistors R
and R
divide
the voltage at the arm of the pot to supply a
±
7.5 mW
adjustment range with
±
15V supplies.
This adjustment method is also useful when the feedback
element is a capacitor or non-linear device.
This technique of supplying a small voltage effectively in
series with the input is also used for adjusting non-inverting
amplifiers. As is shown in
Figure 3
, divider R
1
, R
2
reduces
the voltage at the arm of the pot to
±
7.5 mW for offset
adjustment. Since R
2
appears in series with R
4
, R
2
should
be considered when calculating the gain. If R
4
is greater than
10 k
the error due to R
2
is less than 1%.
00846001
R1 = 2000 R3
\
R4
R4
\
R3
≤
10 k
FIGURE 1. Offset Voltage Adjustment for Inverting
Amplifiers Using 10 k
Source Resistance or Less
00846002
FIGURE 2. Offset Voltage Adjustment for Inverting
Amplifiers Using Any Type of Feedback Element
National Semiconductor
Linear Brief 9
August 1969
U
L
2002 National Semiconductor Corporation
AN008460
www.national.com
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