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PDF AD625 Data sheet ( Hoja de datos )
| Número de pieza | AD625 | |
| Descripción | Programmable Gain Instrumentation Amplifier | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de AD625 (archivo pdf) en la parte inferior de esta página. Total 15 Páginas | ||
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FEATURES
User Programmed Gains of 1 to 10,000
Low Gain Error: 0.02% Max
Low Gain TC: 5 ppm/؇C Max
Low Nonlinearity: 0.001% Max
Low Offset Voltage: 25 V
Low Noise 4 nV/√Hz (at 1 kHz) RTI
Gain Bandwidth Product: 25 MHz
16-Lead Ceramic or Plastic DIP Package,
20-Terminal LCC Package
Standard Military Drawing Available
MlL-Standard Parts Available
Low Cost
Programmable Gain
Instrumentation Amplifier
AD625
FUNCTIONAL BLOCK DIAGRAM
–INPUT
–GAIN
SENSE
–GAIN
DRIVE
50⍀
–+
+GAIN
DRIVE
+GAIN
SENSE
+INPUT
50⍀ – +
–+
VB
AD625
10k⍀
10k⍀
10k⍀
–
+
10k⍀
–+
SENSE
OUTPUT
REFERENCE
PRODUCT DESCRIPTION
The AD625 is a precision instrumentation amplifier specifically
designed to fulfill two major areas of application: 1) Circuits re-
quiring nonstandard gains (i.e., gains not easily achievable with
devices such as the AD524 and AD624). 2) Circuits requiring a
low cost, precision software programmable gain amplifier.
For low noise, high CMRR, and low drift the AD625JN is the
most cost effective instrumentation amplifier solution available.
An additional three resistors allow the user to set any gain from
1 to 10,000. The error contribution of the AD625JN is less than
0.05% gain error and under 5 ppm/°C gain TC; performance
limitations are primarily determined by the external resistors.
Common-mode rejection is independent of the feedback resistor
matching.
A software programmable gain amplifier (SPGA) can be config-
ured with the addition of a CMOS multiplexer (or other switch
network), and a suitable resistor network. Because the ON
resistance of the switches is removed from the signal path, an
AD625 based SPGA will deliver 12-bit precision, and can be
programmed for any set of gains between 1 and 10,000, with
completely user selected gain steps.
For the highest precision the AD625C offers an input offset
voltage drift of less than 0.25 µV/°C, output offset drift below
15 µV/°C, and a maximum nonlinearity of 0.001% at G = 1. All
grades exhibit excellent ac performance; a 25 MHz gain band-
width product, 5 V/µs slew rate and 15 µs settling time.
The AD625 is available in three accuracy grades (A, B, C) for
industrial (–40°C to +85°C) temperature range, two grades (J,
K) for commercial (0°C to +70°C) temperature range, and one
(S) grade rated over the extended (–55°C to +125°C) tempera-
ture range.
PRODUCT HIGHLIGHTS
1. The AD625 affords up to 16-bit precision for user selected
fixed gains from 1 to 10,000. Any gain in this range can be
programmed by 3 external resistors.
2. A 12-bit software programmable gain amplifier can be config-
ured using the AD625, a CMOS multiplexer and a resistor
network. Unlike previous instrumentation amplifier designs,
the ON resistance of a CMOS switch does not affect the gain
accuracy.
3. The gain accuracy and gain temperature coefficient of the
amplifier circuit are primarily dependent on the user selected
external resistors.
4. The AD625 provides totally independent input and output
offset nulling terminals for high precision applications. This
minimizes the effects of offset voltage in gain-ranging
applications.
5. The proprietary design of the AD625 provides input voltage
noise of 4 nV/√Hz at 1 kHz.
6. External resistor matching is not required to maintain high
common-mode rejection.
REV. D
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 2000
1 page  
20
15
10
25؇C
5
0
0 5 10 15 20
SUPPLY VOLTAGE – ؎V
Figure 1. Input Voltage Range vs.
Supply Voltage, G = 1
Typical Performance Characteristics–AD625
20 30
15
20
10
10
5
0
0 5 10 15 20
SUPPLY VOLTAGE – ؎V
Figure 2. Output Voltage Swing
vs. Supply Voltage
0
10 100 1k 10k
LOAD RESISTANCE – ⍀
Figure 3. Output Voltage Swing
vs. Load Resistance
–160
–140 G = 1000
–120 G = 100
–100 G = 10
–80 G = 1
–60
–40
–20
0
0 10 100 1k 10k 100k 10M
FREQUENCY – Hz
Figure 4. CMRR vs. Frequency
RTI, Zero to 1 kΩ Source Imbal-
ance
30
G = 1, 100
20
G = 500
BANDWIDTH
LIMITED
10
G = 100
G = 1000
0
1k 10k 100k
FREQUENCY – Hz
1M
Figure 5. Large Signal Frequency
Response
1000
100
10
1
100 1k
10k 100k
1M 10M
FREQUENCY – Hz
Figure 6. Gain vs. Frequency
–1
0
1
2
3
4
5
6
7
0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
WARM-UP TIME – Minutes
Figure 7. Offset Voltage, RTI, Turn
On Drift
160
140
G = 500
120
G = 100
100
G=1
80
–VS = –15V dc+
1V p-p SINEWAVE
60
40
20
0
10 100 1k 10k 100k
FREQUENCY – Hz
Figure 8. Negative PSRR vs.
Frequency
160
140
G = 500
120
G = 100
100
G=1
80
+VS = +15V dc+
1V p-p SINEWAVE
60
40
20
0
10 100 1k 10k 100k
FREQUENCY – Hz
Figure 9. Positive PSRR vs.
Frequency
REV. D
–5–
5 Page 
AD625
Offset voltage and offset voltage drift each have two compo-
nents: input and output. Input offset is that component of offset
that is generated at the input stage. Measured at the output it is
directly proportional to gain, i.e., input offset as measured at the
output at G = 100 is 100 times greater than that measured at
G = 1. Output offset is generated at the output and is constant
for all gains.
The input offset and drift are multiplied by the gain, while the
output terms are independent of gain, therefore, input errors
dominate at high gains and output errors dominate at low gains.
The output offset voltage (and drift) is normally specified at
G = 1 (where input effects are insignificant), while input offset
(and drift) is given at a high gain (where output effects are negli-
gible). All input-related parameters are specified referred to the
input (RTI) which is to say that the effect on the output is “G”
times larger. Offset voltage vs. power supply is also specified as
an RTI error.
By separating these errors, one can evaluate the total error inde-
pendent of the gain. For a given gain, both errors can be com-
bined to give a total error referred to the input (RTI) or output
(RTO) by the following formula:
Total Error RTI = input error + (output error/gain)
Total Error RTO = (Gain × input error) + output error
The AD625 provides for both input and output offset voltage
adjustment. This simplifies nulling in very high precision appli-
cations and minimizes offset voltage effects in switched gain
applications. In such applications the input offset is adjusted
first at the highest programmed gain, then the output offset is
adjusted at G = 1. If only a single null is desired, the input offset
null should be used. The most additional drift when using only
the input offset null is 0.9 µV/°C, RTO.
COMMON-MODE REJECTION
Common-mode rejection is a measure of the change in output
voltage when both inputs are changed by equal amounts. These
specifications are usually given for a full-range input voltage
change and a specified source imbalance.
In an instrumentation amplifier, degradation of common-mode
rejection is caused by a differential phase shift due to differences
in distributed stray capacitances. In many applications shielded
cables are used to minimize noise. This technique can create
+INPUT
100⍀
AD711
+VS
RF
RG AD625
RF
SENSE
VOUT
–INPUT
REFERENCE
–VS
Figure 32. Common-Mode Shield Driver
common-mode rejection errors unless the shield is properly
driven. Figures 32 and 33 show active data guards which are
configured to improve ac common-mode rejection by “boot-
strapping” the capacitances of the input cabling, thus minimiz-
ing differential phase shift.
100⍀
+INPUT
AD712
100⍀
RF
RG
–VS RF
+VS
AD625
SENSE
VOUT
REFERENCE
–INPUT
–VS
Figure 33. Differential Shield Driver
GROUNDING
In order to isolate low level analog signals from a noisy digital
environment, many data-acquisition components have two or
more ground pins. These grounds must eventually be tied to-
gether at one point. It would be convenient to use a single
ground line, however, current through ground wires and pc runs
of the circuit card can cause hundreds of millivolts of error.
Therefore, separate ground returns should be provided to mini-
mize the current flow from the sensitive points to the system
ground (see Figure 34). Since the AD625 output voltage is
developed with respect to the potential on the reference termi-
nal, it can solve many grounding problems.
REV. D
INPUT
SIGNAL
AD7502
AD625
–VS
+VS
HOLD
CAP
AD583
SAMPLE
AND
HOLD
–VS +VS
STATUS
ANALOG
OUT
+VS
AD574A
A/D
CONVERTER
–VS
VLOGIC
+VS –VS
DIGITAL
COMMON
ANALOG POWER
GROUND
Figure 34. Basic Grounding Practice for a Data Acquisition System
–11–
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet AD625.PDF ] | |
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