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參數(shù)資料
| 型號： | op495 |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | Rail to Rail Quad OP AMP(滿幅度四運算放大器) |
| 中文描述： | 軌至軌四路運算放大器（滿幅度四運算放大器） |
| 文件頁數(shù)： | 7/12頁 |
| 文件大?。?/td> | 337K |
| 代理商： | OP495 |
OP295/OP495
REV. B
–7–
APPLIC AT IONS
Rail-to-Rail Applications Information
T he OP295/OP495 has a wide common-mode input range ex-
tending from ground to within about 800 mV of the positive
supply. T here is a tendency to use the OP295/OP495 in buffer
applications where the input voltage could exceed the common-
mode input range. T his may initially appear to work because of
the high input range and rail-to-rail output range. But above the
common-mode input range the amplifier is, of course, highly
nonlinear. For this reason it is always required that there be
some minimal amount of gain when rail-to-rail output swing is
desired. Based on the input common-mode range this gain
should be at least 1.2.
Low Drop-Out Reference
T he OP295/OP495 can be used to gain up a 2.5 V or other low
voltage reference to 4.5 volts for use with high resolution A/D
converters that operate from +5 volt only supplies. T he circuit
in Figure 1 will supply up to 10 mA. Its no-load drop-out volt-
age is only 20 mV. T his circuit will supply over 3.5 mA with a
+5 volt supply.
16k
V
OUT
= 4.5V
1 TO 10
μ
F
10
0.001
μ
F
20k
REF43
2
6
4
+5V
+5V
1/2
OP295/
OP495
Figure 1. 4.5 Volt, Low Drop-Out Reference
Low Noise, Single Supply Preamplifier
Most single supply op amps are designed to draw low supply
current, at the expense of having higher voltage noise. T his
tradeoff may be necessary because the system must be powered
by a battery. However, this condition is worsened because all
circuit resistances tend to be higher; as a result, in addition to
the op amp’s voltage noise, Johnson noise (resistor thermal
noise) is also a significant contributor to the total noise of the
system.
T he choice of monolithic op amps that combine the characteris-
tics of low noise and single supply operation is rather limited.
Most single supply op amps have noise on the order of 30 nV/
√
Hz
to 60 nV/
√
Hz
and single supply amplifiers with noise below
5 nV/
√
Hz
do not exist.
In order to achieve both low noise and low supply voltage opera-
tion, discrete designs may provide the best solution. T he circuit
on Figure 2 uses the OP295/OP495 rail-to-rail amplifier and a
matched PNP transistor pair—the MAT 03—to achieve zero-in/
zero-out single supply operation with an input voltage noise of
3.1 nV/
√
Hz
at 100 Hz. R5 and R6 set the gain of 1000, making
this circuit ideal for maximizing dynamic range when amplifying
low level signals in single supply applications. T he OP295/OP495
provides rail-to-rail output swings, allowing this circuit to oper-
ate with 0 to 5 volt outputs. Only half of the OP295/OP495 is
used, leaving the other uncommitted op amp for use elsewhere.
MAT- 03
5
6
3
2
1
7
R3
R4
Q1
Q2
R1
R6
10
V
OUT
LED
1
8
4
3
2
R5
10k
C2
10
μ
F
R7
510
C1
1500pF
R8
100
R2
27k
V
IN
0.1
μ
F
10
μ
F
Q2
2N3906
OP295/
OP495
Figure 2. Low Noise Single Supply Preamplifier
T he input noise is controlled by the MAT 03 transistor pair and
the collector current level. Increasing the collector current re-
duces the voltage noise. T his particular circuit was tested with
1.85 mA and 0.5 mA of current. Under these two cases, the in-
put voltage noise was 3.1 nV/
√
Hz
and 10 nV/
√
Hz
, respectively.
T he high collector currents do lead to a tradeoff in supply cur-
rent, bias current, and current noise. All of these parameters will
increase with increasing collector current. For example, typically
the MAT 03 has an h
FE
= 165. T his leads to bias currents of
11
μ
A and 3
μ
A, respectively. Based on the high bias currents,
this circuit is best suited for applications with low source imped-
ance such as magnetic pickups or low impedance strain gages.
Furthermore, a high source impedance will degrade the noise
performance. For example, a 1 k
resistor generates 4 nV/
√
Hz
of broadband noise, which is already greater than the noise of
the preamp.
T he collector current is set by R1 in combination with the LED
and Q2. T he LED is a 1.6 V “Zener” that has a temperature co-
efficient close to that of Q2’s base-emitter junction, which pro-
vides a constant 1.0 V drop across R1. With R1 equal to 270
,
the tail current is 3.7 mA and the collector current is half that,
or 1.85 mA. T he value of R1 can be altered to adjust the collec-
tor current. Whenever R1 is changed, R3 and R4 should also be
adjusted. T o maintain a common-mode input range that in-
cludes ground, the collectors of the Q1 and Q2 should not go
above 0.5 V—otherwise they could saturate. T hus, R3 and R4
have to be small enough to prevent this condition. T heir values
and the overall performance for two different values of R1 are
summarized in T able I. Lastly, the potentiometer, R8, is needed
to adjust the offset voltage to null it to zero. Similar perfor-
mance can be obtained using an OP90 as the output amplifier
with a savings of about 185
μ
A of supply current. However, the
output swing will not include the positive rail, and the band-
width will reduce to approximately 250 Hz.
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| OP495AY/883 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Voltage-Feedback Operational Amplifier |
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| OP495GP | 制造商:Analog Devices 功能描述:OP Amp Quad GP R-R O/P 制造商:Rochester Electronics LLC 功能描述:QUAD RAIL-TO-RAIL AMP IC - Bulk 制造商:Analog Devices 功能描述:AMPLIFIER IC NUMBER OF CIRCUITS:1 |
| OP495GPZ | 功能描述:IC OPAMP GP R-R 85KHZ QUAD 14DIP RoHS:是 類別:集成電路 (IC) >> Linear - Amplifiers - Instrumentation 系列:- 標準包裝:2,500 系列:- 放大器類型:通用 電路數(shù):4 輸出類型:- 轉(zhuǎn)換速率:0.6 V/µs 增益帶寬積:1MHz -3db帶寬:- 電流 - 輸入偏壓:45nA 電壓 - 輸入偏移:2000µV 電流 - 電源:1.4mA 電流 - 輸出 / 通道:40mA 電壓 - 電源，單路/雙路(±):3 V ~ 32 V，±1.5 V ~ 16 V 工作溫度:0°C ~ 70°C 安裝類型:表面貼裝 封裝/外殼:14-TSSOP（0.173"，4.40mm 寬） 供應(yīng)商設(shè)備封裝:14-TSSOP 包裝:帶卷 (TR) 其它名稱:LM324ADTBR2G-NDLM324ADTBR2GOSTR |
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