MLX90609

Angular Rate Sensor (Standard version)

390109060901

Page 8 of 22

Data Sheet

Rev 008

February/08

5. Detailed Description

5.1 The Working Principle

The MLX90609 is a Z-axis rate-sensing device, also called yaw-rate sensing. It produces an analog

positive going output voltage for clockwise (CW) rotation around the axis normal to the package

top, i.e., clockwise when looking down at the package lid as well as a digital SPI signal proportional

to the angular rate.

Figure 5-1. Angular rate (positive for clockwise rotation) to voltage output

The sensor is a MEMS gyroscope sensitive to Coriolis forces. To create a Coriolis force a

movement must be induced. The gyro has an actuated oscillating mechanical structure (primary

mode). The Coriolis force creates a second oscillating movement when the gyroscope rotates

(secondary mode). As Coriolis force is usually extremely weak the primary mode is driven into

resonance to keep the mechanical noise level low for the signal bandwidth used and to have a

good sensitivity. A capacitance change in the secondary mode is detected and transformed into an

output voltage by the electronic interface circuitry.

The electronic interface must convert a change in the sensor capacitance ∆C into a change in

transducer output voltage VOUT according to the following transfer equation:

e

AngularRat

Gain

Bias

V

OUT

∗

+

=

The bias and gain are adjustable over temperature in order to compensate for the TC of sensor and

readout. After adjusting the bias and gain values and after setting operating mode switches during

the calibration process the transducer output voltage versus angular rate must stay as shown in

Figure 5-1 over the specified temperature range.