Sensors

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Freescale Semiconductor, Inc.

MMA16xxKW

3.5

Acceleration Signal Path

3.5.1

Transducer

The device transducer is an overdamped mass-spring-damper system described by the following transfer function:

where:

ζ = Damping Ratio

Reference Section 2.8 for transducer parameters.

3.5.2

ΣΔ Converter

The sigma delta converter provides the interface between the g-cell and the DSP block. The output of the

ΣΔ converter is a

data stream at a nominal frequency of 1 MHz.

Figure 12.

ΣΔ Converter Block Diagram

3.5.3

Digital Signal Processing Block

A digital signal processing (DSP) block is used to perform signal filtering and compensation operations. A diagram illustrating

Figure 13. Signal Chain Diagram

Hs

()

ω

n

2

s

2

2

ξω

n

s

⋅⋅

⋅

ω

n

2

++

------------------------------------------------------

=

1-BIT

QUANTIZER

FIRST

INTEGRATOR

SECOND

INTEGRATOR

g-cell

ΣΔ_OUT

V =

ADC

DAC

V =

ΣΔ_OUT

Sinc Filter

1z D

–

–

D1

z 1

–

–

()

×

---------------------------------

3

a

0

n

11

n

12

z 1

–

⋅

()

n

13

z 2

–

⋅

()

++

d

11

d

12

z 1

–

⋅

()

d

13

z 2

–

⋅

()

++

-----------------------------------------------------------------------------

n

21

n

22

z 1

–

⋅

()

n

23

z 2

–

⋅

()

++

d

21

d

22

z 1

–

⋅

()

d

23

z 2

–

⋅

()

++

-----------------------------------------------------------------------------

⋅⋅

Low-Pass Filter

Output

OUTPUT

Compensation

A

B

E

C

D

F

Interpolation

Scaling