PSB4860HV4.1 Lantiq, PSB4860HV4.1 Datasheet - Page 30

• Manufacturer Part Number: PSB4860HV4.1
• Manufacturer: Lantiq

Specifications of PSB4860HV4.1

• Lead Free Status / Rohs Status: Supplier Unconfirmed

Data Sheet
The echo suppression unit attenuates the receive or transmit path dependent on what
path is active. Without the echo cancellation unit and by using a high attenuation of the
echo suppression unit, the echo suppression unit provides a half-duplex speakerphone.
If the echo cancellation unit is active but cannot provide all of the required attenuation
itself, the echo suppression unit can be used to provide additional attenuation.
The echo cancellation must be disabled during recording or playback of speech data but
the echo suppression unit can run simultenously. This allows half-duplex speakerphone
operation even when recording or playback is on-going.
2.1.2
A simplified block diagram of the echo cancellation unit is shown in figure 13.
Figure 13 Echo Cancellation Unit - Block Diagram
The echo cancellation unit consists of a finite impulse response filter (FIR) that models
the expected acoustic echo, an NLMS based adaptation unit and a control unit. The
expected echo is subtracted from the actual input signal of the microphone. If the model
is exact and the echo does not exceed the length of the filter then the echo can be
cancelled completely. However, even if this ideal state can be achieved for one moment
the acoustic echo usually changes over time. Therefore the NLMS unit continuously
adapts the coefficients of the FIR filter. This adaptation process is steered by the control
unit. As an example, the adaptation is disabled as long as double talk is detected by the
control unit. Furthermore the control unit informs the echo suppression unit about the
achieved echo return loss.
Table 3 shows the registers associated with the echo cancellation unit.
loudspeaker
microphone
Echo Cancellation
Control
NLMS
30
Filter
FIR
-
PSB 4860
line out
line in
2000-01-14