廬
APPLICATION BULLETIN
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
EXTENDING THE COMMON-MODE RANGE
OF DIFFERENCE AMPLIFIERS
By R. Mark Stitt (602) 746-7445
Extending the common-mode range of difference amplifiers
allows their use in a wider variety of reduced power-supply
applications.
The INA117 has a specified common-mode input range of
鹵200V
when operating on standard
鹵15V
power supplies. At
power-supply voltages above
鹵13V,
the INA117 input range
is limited to
鹵200V
by the power capabilities of its internal
input resistors. On reduced power supplies, the input range
is limited by the common mode input range of the internal
op amp.
The linear common-mode input range of the internal op amp
extends to within 3V of its power supply voltage. For
example, with a
鹵15V
power supply, the common-mode
input range of the internal op amp is
鹵12V.
Because the
INA117 internal resistor network divides the input by 20, the
actual input range of the INA117 would be 20 鈥?(鹵12V), or
240V, for
鹵15V
power supplies. Similarly, reducing the
power supply voltage to
鹵6V
will limit the input common-
mode voltage to
鹵60V.
There are two approaches to boosting the common-mode
input range for reduced power supply applications: Offset-
ting the common-mode range by a fixed amount, and dy-
namically adjusting the common-mode range to follow the
input common-mode signal.
OFFSETTING THE INPUT COMMON-MODE
RANGE WITH A CONSTANT VOLTAGE
In many applications, the common-mode signal range is
known and the common-mode input range of the difference
amplifier can be adjusted to coincide with the required
range. For example, the
鹵60V
common-mode range of the
INA117 operating on
鹵6V
supplies could be shifted to range
from +0V to +120V, or +50V to +170V.
To offset the common-mode range, the reference connection
of the difference amplifier is connected to an offsetting
voltage, V
X
, instead of ground. With the reference connected
to an offsetting potential, a second difference amplifier must
be used to refer the output back to ground.
One way to offset the input voltage is to connect the
reference pins 1 and 5 to the negative supply voltage as
shown in Figure 1. Another possibility is to derive the offset
voltage from a zener diode connected to the negative power
supply as shown in Figure 2. In either case, the total
common-mode range of the INA117 is unchanged and
shifted by 鈥?9 鈥?(V
X
).
V+
7
R
1
380k鈩?/div>
R
2
380k鈩?/div>
7
R
3
380k鈩?/div>
R
1
25k鈩?/div>
R
2
25k鈩?/div>
V
2
2
6
2
5
V
3
3
R
5
21.1k鈩?/div>
8
1
5
R
4
20k鈩?/div>
4
6
A
1
INA117
3
R
3
25k鈩?/div>
A
2
R
4
25k鈩?/div>
INA105
1
V
O
= V
3
鈥?V
2
鈥?V > V
O
> 鈥?0V
Swap A
2
pins 2 and 3 for:
10V > V
O
> 3V
also;
((V+) 鈥?5V) > V
O
> ((V鈥? + 3V)
V鈥?/div>
4
V
X
= V鈥?/div>
FIGURE 1. Offsetting the INA117 Common-Mode Input Range Using the Negative Power Supply as a Reference.
漏
1990 Burr-Brown Corporation
AB-015
AB-015
Printed in U.S.A. August, 1990
AB-015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
-
英文版
AB-003 - VOLTAGE-REFERENCE FILTERS
ETC
-
英文版
AB-004 - MAKE A PRECISION -10V REFERENCE
ETC
-
英文版
AB-005 - Make A Precision -10V Reference
ETC
-
英文版
AB-006 - Make a -10V to +10V Adjustable Precision Voltage So...
ETC
-
英文版
AB-007 - CLASSICAL OP AMP OR CURRENT-FEEDBACK OP AMP?
ETC
-
英文版
AB-008 - AC COUPLING INSTRUMENTATION AND DIFFERENCE AMPLIFIE...
ETC
-
英文版
AB-009 - SINGLE-SUPPLY OPERATION OF ISOLATION AMPLIFIERS
ETC
-
英文版
AB-010 - -200V DIFFERENCE AMPLIFIER WITH COMMON-MODE VOLTAGE...
ETC
-
英文版
AB-011 - LOW POWER SUPPLY VOLTAGE OPERATION OF REF102 10.0V ...
ETC
-
英文版
AB-012 - BOOST ISO120 BANDWIDTH TO MORE THAN 100kHz
ETC
-
英文版
AB-013 - INCREASING ADC603 INPUT RANGE
ETC
-
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
-
英文版
AB-016 - BOOST AMPLIFIER OUTPUT SWING WITH SIMPLE MODIFICATI...
ETC
-
英文版
AB-017 - Sallen-Key Low-Pass Filter Design Program
ETC
-
英文版
AB-018 - 0 TO 20mA RECEIVER USING RCV420
ETC
-
英文版
AB-019 - USING THE ADS7800 12 BIT ADC WITH UNIPOLAR INPUT SI...
ETC
-
英文版
AB-020 - BURR-BROWN SPICE BASED MACROMODELS. REV. F
ETC
1
2
3
4
5
