PSB21373HV11XT Infineon Technologies, PSB21373HV11XT Datasheet - Page 124

• Manufacturer Part Number: PSB21373HV11XT
• Manufacturer: Infineon Technologies
• Type: PCMr

Specifications of PSB21373HV11XT

• Number Of Channels: 1
• Number Of Adc's: 1
• Number Of Dac's: 1
• Number Of Adc Inputs: 1
• Pin Count: 44
• Mounting: Surface Mount
• Lead Free Status / RoHS Status: Compliant

PSB 21373
•
Figure 64
Speech Detector Signal Flow Graph
4.4.3.1
Background Noise Monitor
The tasks of the noise monitor are to differentiate voice signals from background noise,
even if it exceeds the voice level, and to recognize voice signals without any delay.
Therefore the background noise monitor consists of the low-pass filter 2 (LP2) and the
offset in two separate branches. Basically it works on the burst-characteristic of the
speech: voice signals consist of short peaks with high power (bursts). In contrast,
background noise can be regarded approximately stationary from its average power.
Low-pass filter 2 provides different time constants for noise (non-detected speech) and
speech. It determines the average of the noise reference level. In case of background
noise the level at the output of LP2 is approximately the level of the input. Due to the
offset OFF the comparator remains in the initial state. In case of speech at the
comparator input the difference between the signal levels of the offset branch and of the
LP2-branch increases and the comparator changes state. At speech bursts the digital
signals arriving at the comparator via the offset branch change faster than those via the
LP2-branch so that the comparator changes its polarity. Hence two logical levels are
generated: one for speech and one for noise.
Data Sheet
124
2002-05-13