MT9123 Ver la hoja de datos (PDF) - Mitel Networks
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MT9123 Datasheet PDF : 32 Pages
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MT9123
Preliminary Information
Echo Canceller A, Flat Delay Register
Echo Canceller B, Flat Delay Register
FD
FD7
FD6
FD5
FD4
FD3
FD2
7
6
5
4
3
2
Echo Canceller A, Decay Step Number Register
Echo Canceller B, Decay Step Number Register
NS
NS7
NS6
NS5
NS4
NS3
NS2
7
6
5
4
3
2
ADDRESS = 04h WRITE/READ VERIFY
ADDRESS = 24h WRITE/READ VERIFY
FD1
FD0
1
0
Power Reset Value
00h
ADDRESS = 07h WRITE/READ VERIFY
ADDRESS = 27h WRITE/READ VERIFY
NS1
NS0
1
0
Power Reset Value
00h
Echo Canceller A, Decay Step Size Control Register
Echo Canceller B, Decay Step Size Control Register
ADDRESS = 06h WRITE/READ VERIFY
ADDRESS = 26h WRITE/READ VERIFY
SSC
0
0
0
0
0
SSC2 SSC1 SSC0
7
6
5
4
3
2
1
0
Power Reset Value
04h
Note: Bits marked with “0” are reserved bits and should be written “0”.
Amplitude of MU
1.0
FIR Filter Length (512 or 1024 taps)
Step Size (SS)
Flat Delay (FD7-0)
2-16
Time
Number of Steps (NS7-0)
The Exponential Decay registers (Decay Step Number and Decay Step Size) and Flat Delay register allow the LMS adaptation
step-size (MU) to be programmed over the length of the FIR filter. A programmable MU profile allows the performance of the echo
canceller to be optimized for specific applications. For example, if the characteristic of the echo response is known to have a flat
delay of several milliseconds and a roughly exponential decay of the echo impulse response, then the MU profile can be
programmed to approximate this expected impulse response thereby improving the convergence characteristics of the adaptive
filter. Note that in the following register descriptions, one tap is equivalent to 125µs (64ms/512 taps).
FD7-0
Flat Delay: This register defines the flat delay of the MU profile, (i.e., where the MU value is 2-16). The delay is defined
as FD7-0 x 8 taps. For example; if FD7-0 = 5, then MU=2-16 for the first 40 taps of the echo canceller FIR filter. The valid
range of FD7-0 is: 0 <= FD7-0 <= 64 in normal mode and 0 <= FD7-0 <= 128 in extended-delay mode. The default value of
FD7-0 is zero.
SSC2-0
Decay Step Size Control: This register controls the step size (SS) to be used during the exponential decay of MU. The
decay rate is defined as a decrease of MU by a factor of 2 every SS taps of the FIR filter, where SS = 4 x2SSC2-0. For
example; If SSC2-0 = 4, then MU is reduced by a factor of 2 every 64 taps of the FIR filter. The default value of SSC2-0
is 04h.
NS7-0
Decay Step Number: This register defines the number of steps to be used for the decay of MU where each step has a
period of SS taps (see SSC2-0). The start of the exponential decay is defined as:
Filter Length (512 or 1024) - [ Decay Step Number (NS7-0) x Step Size (SS) ] where SS = 4 x2SSC2-0.
For example, if NS7-0=4 and SSC2-0=4, then the exponential decay start value is 512 - [NS7-0 x SS] = 512 - [4 x (4x24)] =
256 taps for a filter length of 512 taps.
8-62
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