mt90502ag2 Zarlink Semiconductor, mt90502ag2 Datasheet - Page 93

• Manufacturer Part Number: mt90502ag2
• Description: Multi-channel Aal2 Sar
• Manufacturer: Zarlink Semiconductor

2.9.3.1
PCM Law Table
PCM A-law and µ-law translation is supported by MT90502 on a per channel basis. For RX PCM channel, input law
(from received CPS packet) and output law (sent on TDM bus) are controlled through RX TDM Control Memory
Structures as shown in Figure 29, “RX Channel Association Memory (RX CAM),” on page 65.
For TX PCM channels, law translation is configured in PCM Law Table located at 1000h-11FEh.
DC Offset Calculation
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 98) 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.
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 Silent Suppression Operation
1000h
1002h
ch[x]:
b15 b14
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
b13 b12
b11 b10
Figure 53 - PCM Law Table
Zarlink Semiconductor Inc.
MT90502
b9 b8
93
ch[0]
ch[4]
b7 b6
...
ch[1]
ch[5]
b5 b4
...
ch[2]
ch[6]
b3 b2
...
ch[3]
ch[7]
b1 b0
...
Data Sheet