AN-763 [ADI]
Dual Universal Precision Op Amp Evaluation Board; 双路通用精密运算放大器评估板
| 型号： | AN-763 |
| 厂家： | 
ADI |
| 描述： | Dual Universal Precision Op Amp Evaluation Board |
| 文件： | 总4页 (文件大小：348K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
AN-763
APPLICATION NOTE
One Technology Way • P.O. Box 9106 • Norwood, MA 02062-9106 • Tel: 781/329-4700 • Fax: 781/326-8703 • www.analog.com
Dual Universal Precision Op Amp Evaluation Board
by Giampaolo Marino and Steve Ranta
The EVAL-PRAOPAMP-2R/2RU/2RM is an evaluation board
that accommodates dual op amps in SOIC, TSSOP, and
MSOPpackages. Itprovidestheuserwithmultiplechoices
and extensive flexibility for different application circuits
and configurations.
Choosing equal capacitor values minimizes the sensitivity
and also simplifies the expression for fC to
(3)
The value of Q determines the peaking of the gain versus
frequency (generally ringing in time domain). Commonly
chosen values for Q are near unity.
This board is not intended to be used with high frequency
componentsorhighspeedamplifiers.However,itprovides
the user with many combinations for various circuit types,
including active filters, instrumentation amplifiers, com-
posite amplifiers, and external frequency compensation
circuits. Several examples of application circuits are given
in this application note.
SettingQ=1/÷2yieldsminimumgainpeakingandminimum
ringing. Use Equation 3 to determine the values for R1 and
R2. For example, set Q = 1/÷2, R1/R2 = 2 in the circuit ex-
ample, and pick R1 = 5 k and R2 = 10 k for simplicity.The
second stage is a low-pass filter whose corner frequency
can be determined in a similar fashion:
TWO STAGE BAND-PASS FILTER
C3
680pF
R3 = R4 = R
R2
10k
V–
V–
2
4
R3
R4
6
5
1
4
8
V
C2
C1
33k
33k
OUT
3
7
10nF 10nF
C3
C4
8
1/2 OP2177
and
Q = 1/ 2
1/2 OP2177
C4
330pF
+
V1
–
V+
R1
20k
V+
HALF-WAVE, FULL-WAVE RECTIFIER
Figure 1. KRC Filter
Rectifying circuits are used in a multitude of applications.
One of the most popular uses is in the design of regulated
power supplies where a rectifier circuit is used to convert
an input sinusoid to a unipolar output voltage.There are
somepotentialproblemsforamplifiersusedinthismanner.
When the input voltageVIN is negative, the output is zero.
When the magnitude of VIN is doubled at the input of the
op amp, this voltage could exceed the power supply volt-
age which would damage the amplifiers permanently.The
op amp must come out of saturation whenVIN is negative.
This delays the output signal because the amplifier needs
timetoenteritslinearregion.TheAD8510/AD8512/AD8513
haveveryfastoverdriverecoverytime, whichmakesthem
agreatchoiceforrectificationoftransientsignals.Thesym-
metry of the positive and negative recovery time is also
very important in keeping the output signal undistorted.
The low offset voltage and high CMRR makes the OP2177
a great choice for precision filters such as the KRC filter
shown in Figure 1. This particular filter implementation
offers the flexibility to tune the gain and the cut-off fre-
quency independently. Since the common-mode voltage
into the amplifier varies with the input signal in the KRC
filter circuit, a high CMRR amplifier such as the OP2177
is required to minimize distortion. Furthermore, the low
offsetvoltageoftheOP2177allowsawiderdynamicrange
when the circuit gain is chosen to be high.
ThecircuitinFigure1consistsoftwostages.Thefirststage
is a simple high-pass filter whose corner frequency fC is
1
2π C1C2R1R2
(1)
(2)
and whose
R1
R2
Q = K
K = is the dc gain.
REV. B
AN-763
R2
10k
R3
10k
HIGH GAIN COMPOSITE AMPLIFIER
R1
1k
R2
5V
8
99k
V
EE
V
6
5
IN
4
2/2
3V p-p
V
CC
7
3
2
AD8512
1/2
OUT B
(HALF WAVE)
R1
1k
+
–
8
1
AD8512
AD8603
U5
V–
V+
AD8541
4
V+
V–
V
5V
IN
V
V
EE
CC
OUT A
(HALF WAVE)
R3
1k
R4
99k
Figure 2a. Half-Wave and Full-Wave Rectifier
Figure 3. High Gain Composite Amplifier
A composite amplifier can provide a very high gain in
applications where high closed-loop dc gain is needed.
The high gain achieved by the composite amplifier comes
at the expense of a loss in phase margin.
Placing a small capacitor, CF, in the feedback loop and
in parallel with R2 improves the phase margin. For the
circuit of Figure 3, picking a CF = 50 pF will yield a phase
margin of about 45.
R2
100k
V
EE
AD8603
R1
1k
TIME (1ms/DIV)
V
CC
R3
1k
R4
V–
V+
Figure 2b. Half-Wave Rectifier Signal (Output A)
100
V+
V–
V
IN
C2
AD8541
C3
V
CC
V
EE
Figure 4. Low Power Composite Amplifier
A composite amplifier can be used to optimize the dc
and ac characteristic. Figure 4 shows an example using
the AD8603 and the AD8541 that offers too many circuit
advantages.The bandwidth is increased substantially and
the input offset voltage and noise of theAD8541 becomes
insignificant since they are divided by the high gain of
the AD8603. The circuit offers a high bandwidth, a high
output current, and a very low power consumption of
less than 100 A.
TIME (1ms/DIV)
Figure 2c. Full-Wave Rectifier Signal (Output B)
Figure 2a is a typical representation of a rectifier circuit.
The first stage of the circuit is a half-wave rectifier. When
the sine wave applied at the input is positive, the output
follows the input response. During the negative cycle of
the input, the output tries to swing negative to follow the
input, but the power supplies restrains it to zero. Similarly,
the second stage is a follower during the positive cycle of
the sine wave and an inverter during the negative cycle.
Figure 2b and Figure 2c represents the signal response of
the circuit at Output A and Output B, respectively.
REV. B
–2–
AN-763
EXTERNAL COMPENSATIONTECHNIQUES
Snubber Network
Series Resistor Compensation
Another way to stabilize an op amp driving a capacitive
load is the use of a snubber, as shown in Figure 6a.This
method has the significant advantage of not reducing the
output swing because there is no isolation resistor in the
signal path.Also, the use of the snubber does not degrade
the gain accuracy or cause extra distortion when driving
a nonlinear load.The exact RS and CS combination can be
determined experimentally.
The use of external compensation networks may be
required to optimize certain applications. Figure 5a is a
typicalrepresentationofaseriesresistorcompensationto
stabilizeanopampdrivingcapacitiveloads.Thestabilizing
effect of the series resistor can be thought of as a means
to isolate the op amp output and the feedback network
from the capacitive load. The required amount of series
resistance depends on the part used, but values of 5 to
50 are usually sufficient to prevent local resonance.The
disadvantageofthistechniqueisareductioningainaccuracy
and extra distortion when driving nonlinear loads.
V
OUT
C
R
L
L
R
S
V
IN
C
S
R2
V
OUT
C
R
L
L
Figure 6a. Snubber Network
V
IN
R
C
= 10k
= 500pF
L
L
Figure 5a. Series Resistor Compensation
R
C
= 10k
= 2nF
L
L
GND
TIME (1s/DIV)
Figure 6b. Cap Load Drive Without Snubber
R
C
R
C
= 10k
= 500pF
= 100
= 1nF
L
L
S
S
TIME (10s/DIV)
Figure 5b. Cap Load Drive Without Resistor
R
R
C
C
= 10k
= 200
= 2nF
L
S
L
S
= 0.47F
GND
TIME (1s/DIV)
Figure 6c. Cap Load Drive with Snubber
TIME (10s/DIV)
Figure 5c. Cap Load Drive with Resistor
REV. B
–3–
AN-763
C4
R4
V
EE
1
AMPLIFIER A
R2
C2
–V1
R6
2
1
4
DUTA
1
VO1
R8
1
–INA
Rt1
3
G1
V
A
DUT
OUT
1
R 1
S
R 1
L
8
C 1
L
C1
G1
G5
1
C 1
S
+V1
R7
R5
1
G3
R1
+INA
C3
R3
Rt2
G2
1
1
G2
V
C5
CC
Figure 7. Dual Universal Precision Op Amp Evaluation Board Electrical Schematic
C7
R10
AMPLIFIER B
–V2
R12
6
5
1
7
DUTB
R14
VO2
1
–INB
G3
Rt3
B
V
OUT
1
R 2
R 2
C 2
DUT
L
S
L
G3
G6
1
C 2
S
+V2
R13
R11
1
G6
+INB
G4
C6
R9
Rt4
1
G4
C8
Figure 8. Dual Universal Precision Op Amp Evaluation Board
Figure 9. Layout Patterns
© 2012 Analog Devices, Inc. All rights reserved.Trademarks and registered trademarks are the property of their respective owners.
AN05284-0-9/12(B)
REV. B
–4–
相关型号：
AN-8019
Reliable USB Modem Design Using the Combination of an Integrated Load Switch and a Buck Converter
FAIRCHILD
©2020 ICPDF网 联系我们和版权申明