AM417 – Ratiometric instrumentation

amplifier with adjustable output stage

Analog Microelectronics GmbH

An der Fahrt 13, D – 55124 Mainz

July 2008 –Rev 3.1- Page 9/18

Phone:+49 (0)6131/91 073-0

Fax: +49 (0)6131/91 073-30

Internet: http://www.analogmicro.de

Email: info@analogmicro.de

If when calculating

VRO (Equation 11) a negative value is produced, the resistor R0 must be placed

in the left arm of the bridge (

RO’; see Figure 3):

Doing so changes the effective direction of

RO and its resistance is now expressed as:

IB

RO

O

I

V

R

)

(

2

'

−

⋅

=

(12a)

1

7

AM417

C

1

V

OUT

8

V

S

T

1

R

2

C

2

R

3

R

4

6

C

3

Ground

R

9 R

2

3

OP

IA

I

IB

Output-

stage

R

1

4

5

R

B1

R

B2

R

B3

R

B4

V

IN -

V

IN +

R

O

´

Figure 3: Circuit as in Figure 2 with R0’ (instead R0) at input pin 5 (IN-)