Mailing Address: PO Box 11400 鈥?Tucson, AZ 85734 鈥?Street Address: 6730 S. Tucson Blvd. 鈥?Tucson, AZ 85706
Tel: (602) 746-1111 鈥?Twx: 910-952-111 鈥?Telex: 066-6491 鈥?FAX (602) 889-1510 鈥?Immediate Product Info: (800) 548-6132
DIFFERENCE AMPLIFIER 鈥?/div>
INA105 AND INA106 G = 1, 10 DIFFERENCE AMPLIFIERS 鈥?INA101, INA102, INA103, INA110, INA120
INSTRUMENTATION AMPLIFIERS
By R. Mark Stitt (602) 746-7445
The need to glean AC signals from DC in the presence of
common-mode noise frequently occurs in signal condition-
ing applications. AC coupling to an instrumentation ampli-
fier (IA) or difference amplifier can be used to accurately
extract the AC signal while rejecting DC and common-mode
noise.
Adding capacitors and resistors to AC couple the inputs of
an instrumentation amplifier or difference amplifier seems
like an obvious approach for AC coupling, but it has prob-
lems. The DC restoration circuits shown in this bulletin have
the same transfer function but without the foibles.
Common-mode rejection of a difference amplifier depends
on extremely precise matching of input source impedance.
Adding RC networks to the inputs of either an IA or a
difference amplifier can significantly degrade the CMR,
especially for AC inputs. Even if the CMR is trimmed,
maintaining performance over temperature can be a prob-
lem.
The DC restoration circuits shown solve this problem by
placing a low-pass network in the feedback to the reference
pin of the IA or difference amplifier. The low-pass pole
translates into a high-pass function as referred to the input
with f
鈥?dB
= Gain/2鈥⑾€鈥鈥. The Gain term refers to the Gain
from the reference pin to the output of the IA or difference
amplifier. The selection guide shows this Gain term as the
鈥淗igh-pass multiplier鈥?
R
1
V
2
2
380k鈩?/div>
The DC-restored INA117 is shown in Figure 1. With the
values shown, the high-pass zero is
鈮?.5Hz.
The INA117BM has a CMR of 86dB min. If improved CMR
is required for the DC restored INA117, use the circuit
shown in Figure 2. Since the trim resistors are small, they
will not degrade the stability or drift performance of the
INA117.
The INA117 has a common-mode input range and differen-
tial offset range of up to
鹵200V.
If a lower common-mode
and differential offset range of
鹵100V
is acceptable, the
INA106 can be used for lower noise and twice the small
signal bandwidth (400kHz vs 200kHz).
R
1
V
2
2
380k鈩?/div>
R
2
380k鈩?/div>
R
3
V
3
3
380k鈩?/div>
6
V
OUT
= V
3
鈥?V
2
R
5
21.1k鈩?/div>
R
4
20k鈩?/div>
INA117
8
1
20
鈩?/div>
CMR
Trim
5
10
鈩?/div>
C
1
0.47碌F
R
1
1M鈩?/div>
R
2
380k鈩?/div>
R
3
V
3
3
380k鈩?/div>
6
V
OUT
= V
3
鈥?V
2
OPA602
R
5
21.1k鈩?/div>
R
4
20k鈩?/div>
INA117
8
1
5
C
1
0.47碌F
R
1
1M鈩?/div>
FIGURE 2. AC-Coupled INA117 with CMR Trim.
The simplest circuit for the DC-restored INA106 is shown in
Figure 3. The INA106 is reversed from its normal Gain-of-
10 configuration. The 100k鈩? 10k鈩?resistors form a 11/1
voltage divider on the input so that
鹵100V
at pins 1 and 5 are
divided down to less than
鹵10V
at the op amp inputs. The
R
5
, R
6
network provides the proper feedback Gain for an
overall unity-gain transfer function. Since the precise resis-
tor matching of the INA106 is disturbed by the R
5
, R
6
network this circuit requires trims for both CMR and Gain.
AB-008A
Printed in U.S.A. August, 1991
OPA602
FIGURE 1. AC-Coupled INA117.
漏
1990 Burr-Brown Corporation
AB-008相關(guān)型號PDF文件下載
-
型號
版本
描述
廠商
下載
-
英文版
AB-001 - INCREASING INA117 DIFFERENTIAL INPUT RANGE
ETC
-
英文版
AB-002 - MAKE A PRECISION CURRENT SOURCE OR CURRENT SINK
ETC
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英文版
AB-003 - VOLTAGE-REFERENCE FILTERS
ETC
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英文版
AB-004 - MAKE A PRECISION -10V REFERENCE
ETC
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英文版
AB-005 - Make A Precision -10V Reference
ETC
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英文版
AB-006 - Make a -10V to +10V Adjustable Precision Voltage So...
ETC
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英文版
AB-007 - CLASSICAL OP AMP OR CURRENT-FEEDBACK OP AMP?
ETC
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英文版
AB-008 - AC COUPLING INSTRUMENTATION AND DIFFERENCE AMPLIFIE...
ETC
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英文版
AB-009 - SINGLE-SUPPLY OPERATION OF ISOLATION AMPLIFIERS
ETC
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英文版
AB-010 - -200V DIFFERENCE AMPLIFIER WITH COMMON-MODE VOLTAGE...
ETC
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英文版
AB-011 - LOW POWER SUPPLY VOLTAGE OPERATION OF REF102 10.0V ...
ETC
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英文版
AB-012 - BOOST ISO120 BANDWIDTH TO MORE THAN 100kHz
ETC
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英文版
AB-013 - INCREASING ADC603 INPUT RANGE
ETC
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英文版
AB-014 - INPUT OVERLOAD PROTECTION FOR THE RCV420 4-20mA CUR...
ETC
-
英文版
AB-015 - EXTENDING THE COMMON-MODE RANGE OF DIFFERENCE AMPLI...
ETC
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英文版
AB-016 - BOOST AMPLIFIER OUTPUT SWING WITH SIMPLE MODIFICATI...
ETC
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英文版
AB-017 - Sallen-Key Low-Pass Filter Design Program
ETC
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英文版
AB-018 - 0 TO 20mA RECEIVER USING RCV420
ETC
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英文版
AB-019 - USING THE ADS7800 12 BIT ADC WITH UNIPOLAR INPUT SI...
ETC
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英文版
AB-020 - BURR-BROWN SPICE BASED MACROMODELS. REV. F
ETC
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