參數(shù)資料
型號(hào)： OP484
廠商： Analog Devices, Inc.
英文描述： Precision Rail-to-Rail Input & Output Operational Amplifiers(精密滿幅度輸入輸出運(yùn)放)
中文描述： 精密軌到軌輸入
文件頁(yè)數(shù)： 10/20頁(yè)
文件大?。?/td> 370K
代理商： OP484
REV. 0
–10–
OP184/OP284/OP484
FREQUENCY – Hz
T
0.1
0.010
0.000520
100
10k
1k
0.001
20k
V
O
=
±
0.75V
V
O
=
±
2.5V
V
O
=
±
1.5V
A
V
= 1000
V
S
=
±
2.5V
R
L
= 2k
Figure 40. Total Harmonic Distortion
vs. Frequency
10
0%
100
90
500ns
100mV
V
S
=
±
1.5V
A
V
= 1
NO LOAD
T
A
= +25
°
C
200mV
0V
–200mV
Figure 38. Small Signal Transient
Response
200mV
0V
–200mV
10
0%
100
90
1μs
100mV
V
S
=
±
0.75V
A
V
= 1
NO LOAD
T
A
= +25
°
C
Figure 39. Small Signal Transient
Response
APPLIC AT IONS
Functional Description
T he OP284 and OP484 are precision single-supply, rail-to-rail
operational amplifiers. Intended for the portable instrumenta-
tion marketplace, the OP184/OP284/OP484 combines the at-
tributes of precision, wide bandwidth, and low noise to make it
a superb choice in those single supply applications that require
both ac and precision dc performance. Other low supply voltage
applications for which the OP284 is well suited are active filters,
audio microphone preamplifiers, power supply control, and tele-
com. T o combine all of these attributes with rail-to-rail input/
output operation, novel circuit design techniques are used.
D1
D2
Q4
R2
4k
V
POS
I1
R1
4k
Q3
Q1
Q2
R4
3k
I2
R3
3k
V
01
–IN
V
02
V
NEG
+IN
Figure 41. OP284 Equivalent Input Circuit
For example, Figure 41 illustrates a simplified equivalent circuit
for the OP184/OP284/OP484’s input stage. It is comprised of
an NPN differential pair, Q1-Q2, and a PNP differential pair,
Q3-Q4, operating concurrently. Diode network D1-D2 serves
to clamp the applied differential input voltage to the OP284,
thereby protecting the input transistors against avalanche dam-
age. Input stage voltage gains are kept low for input rail-to-rail
operation. T he two pairs of differential output voltages are con-
nected to the OP284’s second stage which is a compound folded
cascode gain stage. It is also in the second gain stage where the
two pairs of differential output voltages are combined into a
single-ended output signal voltage used to drive the output
stage. A key issue in the input stage is the behavior of the input
bias currents over the input common-mode voltage range. Input
bias currents in the OP284 are the arithmetic sum of the base
currents in Q1-Q3 and in Q2-Q4. As a result of this design
approach, the input bias currents in the OP284 not only exhibit
different amplitudes, but also exhibit different polarities. T his
effect is best illustrated in Figure 8. It is, therefore, of para-
mount importance that the effective source impedances con-
nected to the OP284’s inputs be balanced for optimum dc and
ac performance.
In order to achieve rail-to-rail output, the OP284 output stage
design employs a unique topology for both sourcing and sinking
current. T his circuit topology is illustrated in Figure 42. As
previously mentioned, the output stage is voltage-driven from
the second gain stage. T he signal path through the output stage
is inverting; that is, for positive input signals, Q1 provides the
base current drive to Q6 so that it conducts (sinks) current. For
negative input signals, the signal path via Q1-Q2-D1-Q4-Q3
provides the base current drive for Q5 to conduct (source) cur-
rent. Both amplifiers provide output current until they are
forced into saturation which occurs at approximately 20 mV
from negative rail and 100 mV from the positive supply rail.
V
POS
I2
I1
Q1
Q3
Q4
Q2
V
NEG
Q5
V
OUT
Q6
R6
R3
R2
R1
R4
INPUT FROM
SECOND GAIN
STAGE
R5
D1
Figure 42. OP284 Equivalent Output Circuit
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
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