MT90502 Datasheet, PDF (86/191 Pages) Zarlink Semiconductor Inc – Multi-Channel AAL2 SAR

MT90502
Preliminary Datasheet
b15 b14
1000h
1002h
b13 b12
b11 b10
b9 b8 b7 b6
ch[0]
ch[4]
...
b5 b4
ch[1]
ch[5]
...
b3 b2
ch[2]
ch[6]
...
b1 b0
ch[3]
ch[7]
...
ch[x]: Law translation for TX PCM channel number X.
00 - µ-law to µ-law
01 - µ-law to A-law
10 - A-law to µ-law
11 - No translation
2.9.3.1.2 DC Offset Calculation
Figure 53 - PCM Law Table
The DC component is calculated in both remote and local voice PCM bytes. The MT90502 is able to perform
an accumulation of the PCM linear values over a number of PCM samples (see Local and Remote DC Offset
Figure 61 on page 91) in the reception direction. Accumulation of DC offset is enabled only when CPS-Packet
Assembly Structure is in DC Calculation state. After obtaining DC offsets a short while after a call begins, the
CPU is then required to change the Assembly Structure to Transition state, and write the DC Offset Correction
into the Structure. After that, the Structure can be configured to Suppression state where suppression circuit is
activated. No silence is suppressed in either DC calculation state or Transition state.
2.9.3.1.3 Signal Energy Calculation
To obtain the signal energy, the linear PCM value with consideration of the DC offset correction is squared. The
MT90502 sums all the byte energy values contained in a CPS-Packet and divides the result by the length of the
CPS-Packet to obtain an average energy per byte. Then the MT90502 calculates the linear energy value into
its decibel value.
The same process is employed with ADPCM; however, an external CODEC is required to convert the ADPCM
to PCM. ADPCM silent suppression TDM streams are associated in groups of 4: for example, the ADPCM
channel in transmission is mapped on stream 3, while the local PCM channel is mapped on stream 0, the
ADPCM reception channel is mapped on stream 2, and the remote PCM channel on stream 1 (see Figure 54
and Figure 55).
Complex Silence Suppression TDM Channel Mapping
ct_c8
ct_frame
ct_d[0]
ct_d[1]
ct_d[2]
ct_d[3]
Local ADPCM Nibble
Local PCM Byte
Remote PCM Byte
ct_c8
ct_frame
ct_d[0]
ct_d[1]
Local PCM Byte
Remote PCM Byte
Figure 54 - Complex Silent Suppression Stream Configuration
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