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PSB4860

Digital Answering Machine with Full Duplex Speakerphone SAM EC

Siemens AG 

PSB 4860

Functional Description

2.1

Functional Units

In this section the functional units of the PSB 4860 are described in detail. The functional

units can be individually enabled or disabled.

2.1.1

Full Duplex Speakerphone

The speakerphone unit (figure 10) is attached to four signals (microphone, loudspeaker,

line out and line in). The two input signals (microphone, line in) are preceded by a signal

summation point.

I1

microphone

a

line out

I2

c

o

u

s

t

i

Speakerphone

l

i

n

e

s

c

i

S12

S11

loudspeaker

s

i

d

d

e

line in

I3

e

I4

Figure 10 Speakerphone - Signal Connections

Internally, this unit can be divided into an echo cancellation unit and an echo suppression

unit (figure 11). The echo cancellation unit provides the attenuation Gc while the echo

suppression unit provides the attenuation Gs. The total attenuation ATT of the

speakerphone is therefore ATT=GC+Gs.

microphone

loudspeaker

Echo

Cancellation

Gc

Echo

Suppression

GS

line out

line in

Figure 11 Speakerphone - Block Diagram

The echo suppression unit can be enabled without the echo cancellation unit. If the echo

cancellation unit is disabled, the echo suppression unit still provides speakerphone

functionality, albeit only half duplex. As the echo cancellation must be disabled during

recording or playback of speech data, this option allows for speakerphone operation

Semiconductor Group

27

10.97

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