PSB21473FV13XT Infineon Technologies, PSB21473FV13XT Datasheet - Page 377

• Manufacturer Part Number: PSB21473FV13XT
• Manufacturer: Infineon Technologies

Specifications of PSB21473FV13XT

• Operating Supply Voltage (typ): 3.3V
• Operating Supply Voltage (min): 3.135V
• Operating Supply Voltage (max): 3.6V
• Operating Temp Range: 0C to 70C
• Operating Temperature Classification: Commercial
• Mounting: Surface Mount
• Pin Count: 144
• Lead Free Status / RoHS Status: Compliant

Figure 20-5 Echo Cancellation Unit (Fullband Mode) - 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 from 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 given
moment, the acoustic echo usually changes over the 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 inhibited 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. The length of the FIR can be programmed by
the parameters FBLEN. Furthermore, the number of FIR parameters that are adapted
can be programmed by the parameter FBADA.
With the parameter QU, the echo cancellation unit can be set into two different fullband
modes (section 20.1.1.1). The fullband mode 1 is similar to the mode provided in the PSB
2170 Version 1.1. In this mode, the parameter FBADA has no effect and the noise
reduction cannot be enabled. The delay added in this mode is 0.25 ms. In the fullband
mode two, the delay is shorter than 2 ms. If this delay is not acceptable, the delay can
be reduced to less than 1 ms by setting the bit ERD. The performance of the fullband
mode may suffer in this reduced mode but please note that enabling the noise reduction
will add some additional delay (section 20.1.2).
In order to detect double talk, the remaining speech signal after the echo cancellation
(signal after summation point in figure 20-5) is compared to the signal expected by the
echo cancellation unit (after the signal summation point in figure 20-5). The difference of
the energy of these signals is considered. If this energy is greater than allowed by the
parameter AECDTM, double talk is detected.
Data Sheet
loudspeaker
microphone
Control
NLMS
377
Filter
FIR
Digital Signal Processor
-
PSB 21473
line out
line in
2003-03-31
INCA-D