參數(shù)資料
型號: OP297FSZ-REEL
廠商: Analog Devices Inc
文件頁數(shù): 4/16頁
文件大?。?/td> 0K
描述: IC OPAMP GP 500KHZ DUAL 8SOIC
標(biāo)準(zhǔn)包裝: 2,500
放大器類型: 通用
電路數(shù): 2
轉(zhuǎn)換速率: 0.15 V/µs
增益帶寬積: 500kHz
電流 - 輸入偏壓: 35pA
電壓 - 輸入偏移: 50µV
電流 - 電源: 525µA
電壓 - 電源,單路/雙路(±): 4 V ~ 40 V,±2 V ~ 20 V
工作溫度: -40°C ~ 85°C
安裝類型: 表面貼裝
封裝/外殼: 8-SOIC(0.154",3.90mm 寬)
供應(yīng)商設(shè)備封裝: 8-SO
包裝: 帶卷 (TR)
OP297
Rev. G | Page 12 of 16
NONLINEAR CIRCUITS
Due to its low input bias currents, the OP297 is an ideal log
amplifier in nonlinear circuits such as the square and square
root circuits shown in Figure 35 and Figure 36. Using the
squaring circuit of Figure 35 as an example, the analysis begins
by writing a voltage loop equation across Transistor Q1,
Transistor Q2, Transistor Q3, and Transistor Q4.
+
=
+
S4
REF
T4
S3
OUT
T3
S
IN
T2
S1
IN
T1
I
V
I
V
I
V
I
V
ln
2
All the transistors of the MAT04 are precisely matched and at
the same temperature, so the IS and VT terms cancel, where
2lnIIN = lnIOUT + lnIREF = ln(IOUT × IREF)
Exponentiating both sides of the equation leads to
()
REF
IN
OUT
I
2
=
Op Amp A2 forms a current-to-voltage converter, which gives
VOUT = R2 × IOUT. Substituting (VIN/R1) for IIN and the previous
equation for IOUT yields
2
=
R1
V
I
R2
V
IN
REF
OUT
A similar analysis made for the square root circuit of Figure 36
leads to its transfer function
()(
)
R1
I
V
R2
V
REF
IN
OUT =
7
6
5
–15V
1
2
3
V+
V–
Q3
Q1
Q2
Q4
13
14
12
8
9
10
4
8
6
5
7
2
3
1
MAT04E
+
1/2
OP297
+
1/2
OP297
VIN
R1
33k
C1
100pF
R3
50k
R4
50k
IREF
C2
100pF
R2
33k
VOUT
IOUT
003
00-
035
Figure 35. Squaring Amplifier
7
6
5
IOUT
–15V
1
2
3
V+
V–
Q1
7
9
10
4
8
3
1
MAT04E
8
Q3
5
6
Q4
13
12
14
Q2
R2
33k
C2
100pF
C1
100pF
R1
33k
R3
50k
R4
50k
VOUT
IREF
+
1/2
OP297
+
1/2
OP297
VIN
00300-
036
Figure 36. Square Root Amplifier
In these circuits, IREF is a function of the negative power supply.
To maintain accuracy, the negative supply should be well regu-
lated. For applications where very high accuracy is required, a
voltage reference can be used to set IREF.
An important consideration 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 IREF or R1; R2 can be varied to keep the output
voltage within the usable range.
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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