AM417 – Ratiometric instrumentation

amplifier with adjustable output stage

Analog Microelectronics GmbH

An der Fahrt 13, D – 55124 Mainz

July 2008 –Rev 3.1- Page 10/18

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

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

Email: info@analogmicro.de

EXAMPLES

By way of example the equations shall be calculated using typical values for piezoresistive sensing

elements [2] in an attempt to illustrate how various sensing elements can be calibrated and

compensated with very few external components. The aim of the exercise is to calibrate the output

voltage of AM417 to

Example 1: Piezoresistive pressure sensing element in a bridge circuit with a positive offset

The sensing element is to be supplied with constant current as this provides a simple way of

compensating the temperature behavior of the span (see:

TEMPERATURE COMPENSATION OF

THE OUTPUT SPAN).

Taking the maximum output voltage at pin 2 (

IB) into account the supply current is selected as

At pin 2 (

IB) the voltage is:

V

V

mA

k

V

I

R

V

VR

BR

BR

IB

5

.

3

5

.

0

1

3

=

+

⋅

Ω

=

+

⋅

=

.

Considering a typical positive temperature coefficient of the sensing element bridge resistor

The bridge voltage is:

V

k

mA

R

I

V

BR

BR

BR

3

3

1

'

=

Ω

⋅

=

⋅

=

.

The output voltage of the sensing element given for

bridge voltages:

mV

V

V

mV

V

OUTME

96

5

3

160

'

=

⋅

=

bridge voltages:

mV

V

V

mV

V

OSME

6

5

3

10

'

=

⋅

=

Applying Equation 5 the following is accrued:

166

.

4

10

96

4

=

⋅

=

mV

V

G

OUT