MT90502_06 ZARLINK [Zarlink Semiconductor Inc], MT90502_06 Datasheet - Page 91

• Manufacturer Part Number: MT90502_06
• Description: Multi-Channel AAL2 SAR
• Manufacturer: ZARLINK [Zarlink Semiconductor Inc]

2.9
2.9.1
The Variable Bit Rate properties of the AAL2 standard permits the use of silent suppression. The MT90502 exploits
this feature to enable optimal bandwidth usage for voice communications. The MT90502 has the capability to
determine if an AAL2 CPS-Packet (transmitted or received) is considered silent. Two configurations can be
employed for silent suppression: simple silence suppression and complex silence suppression. Simple silence
suppression mode uses an external resource or the match & mask feature determines the silent status of the byte.
In complex silence suppression mode the MT90502 determines the silent status on the current CPS-Packet. The
MT90502 maintains a maximum channel capacity of 1023 channels with or without silence suppression enabled.
2.9.2
2.9.2.1
Simple Silent Suppression relies upon an external resource to perform the silent decision operation unless the
match and mask method is employed. The result yielded from the external resource is conveyed to the MT90502 by
a silent bit in the associated TSST (see Figure 50 on page 91). A one in silent bit indicates that the accompanying
PCM or ADPCM sample is a silence. The position of silent bit is programmable through register 500h. Upon the
reception of a complete CPS-Packet of silence, the CPS-Packet is considered silent and the process of generating
an SID CPS-Packet is initialized.
The Noise Level field in SID packet will contain an idle code (no noise).
2.9.2.2
This method is only available when TDM Format B is deployed. In this mode, external silence suppression engine
shall make the decision whether a CPS-Packet is silence or voice, and indicate a silent packet by putting 00h on the
last byte of that packet, together with PCM bit equal to 0 (see Figure 9 on page 34 and Figure 11 on page 36).
MT90502 calculates the average energy of the packet based on the Tx PCM unsigned magnitudes received on the
first TSST. Tx PCM magnitude given to MT90502 must be an unsigned value without DC offset. Upon detecting
silent packet pattern at the end of the packet, the MT90502 will discard that packet and start silence period. Should
a SID packet be sent out, MT90502 will insert the calculated energy level into SID byte.
2.9.2.3
The match and mask filtering operation operates in a similar method as the UTOPIA match and mask. There are
two match and mask registers: ‘Silent Pattern Detection Register A’ and ‘Silent Pattern Detection Register B’
address (512h and 514h respectively). The registers are configured to compare selected bits of the PCM value. The
mask field determines which bits to compare and the match field detects silent values. If the byte yields a 0 result
from the match and mask filter, then the byte is regarded as silent. Upon the reception of a complete CPS-Packet of
silence, the CPS-Packet is considered silent and the process of generating an SID CPS-Packet is initialized.
The Noise Level field in SID packet will contain an idle code (no noise).
Silence Suppression
Overview
Simple Silent Suppression
Silent Bit Indication
Last Byte Indication
Match and Mask Determines Silence
n is an even number
Figure 50 - Simple Silent Suppression Stream Configuration
ct_frame
ct_d[n+1]
ct_d[n]
Simple Silence Suppression TDM Channel Mapping
ct_c8
Silent
Zarlink Semiconductor Inc.
ADPCM Nibble or PCM Byte
MT90502
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Data Sheet