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參數資料
| 型號： | OP497 |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | Precision Picoampere Input Current Quad Operational Amplifier |
| 中文描述： | 精密Picoampere輸入電流四路運算放大器 |
| 文件頁數： | 9/12頁 |
| 文件大小： | 302K |
| 代理商： | OP497 |
REV. D
OP497
–9–
2
3
1
7
8
5
6
4
–
5V
+5V
REF43
6
2
4
+5V
R
R
R
2.5 V
R + R
R
F
V
OUT
V
REF
V
OUT
= V
REF
( R + R
R
F
R
1/4
OP497
1/4
OP497
Figure 9. A Simple Bridge Conditioning Amplifier Using
the OP497
NONLINEAR CIRCUITS
Due to its low input bias currents, the OP497 is an ideal log
amplifier in nonlinear circuits such as the square and square
root circuits shown in Figures 10 and 11. Using the squaring
circuit of Figure 10 as an example, the analysis begins by writing a
voltage-loop equation across transistors Q
1
, Q
2
, Q
3
, and Q
4
.
V
In
I
I
V
In
I
I
V
In II
I
V
In
I
I
T
IN
S
T
IN
S
T
O
S
T
REF
S
1
1
2
2
3
3
4
4
+
=
+
All the transistors of the MAT04 are precisely matched and at
the same temperature, so the I
S
and V
T
terms cancel, giving:
2InI
InI
InI
In I
I
IN
O
REF
O
REF
=
+
=
×
)
Exponentiating both sides of thick equation leads to:
I
I
I
O
IN
2
REF
=
(
)
Op amp A
2
forms a current-to-voltage converter which gives
V
OUT
= R2
×
I
O
. Substituting (V
IN
/R1) for I
IN
and the above
equation for I
O
, yields:
V
R2
I
V
R1
OUT
REF
IN
2
=
1
2
3
6
7
5
C1
100pF
V+
2
3
8
1
4
V
–
V
IN
I
IN
C2
100pF
6
5
7
V
OUT
I
O
9
8
10
Q1
Q3
Q2
14
12
Q4
13
–
15V
I
REF
MAT-04E
R1
133k
R2
33k
R3
50k
R4
50k
1/4
OP497
1/4
OP497
Figure 10. Squaring Amplifier
A similar analysis made for the square-root circuit of Figure 11
leads to its transfer function:
V
R2
V
(
I
R1
OUT
IN
REF
=
)(
)
In these circuits, I
REF
is a function of the negative power sup-
ply. To maintain accuracy, the negative supply should be well
regulated. For applications where very high accuracy is required,
a voltage reference may be used to set I
REF
. An important con-
sideration for the squaring circuit is that a sufficiently large
input voltage can force the output beyond the operating range
of the output op amp. Resistor R4 can be changed to scale I
REF
,
or Rl and R2 can be varied to keep the output voltage within
the usable range.
1
2
3
6
7
5
C1
100pF
V+
2
3
8
1
4
V
–
6
5
7
V
OUT
I
O
9
8
10
Q1
Q3
Q2
14
12
Q4
13
–
15V
I
REF
MAT-04E
I
IN
V
IN
R1
33k
R2
33k
R5
2k
R3
50k
R4
50k
C2
100pF
1/4
OP497
1/4
OP497
Figure 11. Square-Root Amplifier
Unadjusted accuracy of the square-root circuit is better than
0.1% over an input voltage range of 100 mV to 10 V. For a
similar input voltage range, the accuracy of the squaring circuit
is better than 0.5%.
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相關代理商/技術參數 |
參數描述 |
|---|---|
| OP-497 | 制造商:AD 制造商全稱:Analog Devices 功能描述:PRECISION PICOAMPERE INPUT CURRENT QUAD OPERATIONAL AMPLIFIER |
| OP4970027SR | 制造商:Analog Devices 功能描述: |
| OP497AY | 制造商:AD 制造商全稱:Analog Devices 功能描述:Precision Picoampere Input Current Quad Operational Amplifier |
| OP-497AY | 制造商:AD 制造商全稱:Analog Devices 功能描述:PRECISION PICOAMPERE INPUT CURRENT QUAD OPERATIONAL AMPLIFIER |
| OP-497BRC/883 | 制造商:AD 制造商全稱:Analog Devices 功能描述:PRECISION PICOAMPERE INPUT CURRENT QUAD OPERATIONAL AMPLIFIER |
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