ZL50234GDC ZARLINK [Zarlink Semiconductor Inc], ZL50234GDC Datasheet - Page 9

• Manufacturer Part Number: ZL50234GDC
• Description: 8 Channel Voice Echo Canceller
• Manufacturer: ZARLINK [Zarlink Semiconductor Inc]

Data Sheet
by the following equation:
where NLPTHR is the Non-Linear Processor Threshold register value and Lrin is the relative power level expressed
in dBm0. The NLPTHR register is 16 bits wide. The register value in hexadecimal can be calculated with the following
equation:
where 0 < NLPTHR
When the level of residual error signal falls below TSUP, the NLP is activated further attenuating the residual signal
by an additional 30 dB. To prevent a perceived decrease in background noise due to the activation of the NLP, a
spectrally-shaped comfort noise, equivalent in power level to the background noise, is injected. This keeps the
perceived noise level constant. Consequently, the user does not hear the activation and de-activation of the NLP.
The NLP processor can be disabled by setting the NLPDis bit to “1” in Control Register 2.
The comfort noise injector can be disabled by setting the INJDis bit to “1” in Control Register 1. It should be noted
that the NLPTHR is valid and the comfort noise injection is active only when the NLP is enabled.
The patented Advanced NLP provides a number of new and improved features over the original NLP found in
previous generation devices. Differences between the Advanced NLP and the original NLP are summarized in Table
1.
The NLPSel bit in Control Register 3 selects which NLP is used. A “1” will select the Advanced NLP, “0” selects the
original NLP. ( See page 29 - Control Register 3 bit description)
The Advanced NLP uses a new noise ramping scheme to quickly and more accurately estimate the background
noise level. The noise ramping method of the original NLP can also be used. The InjCtrl bit in Control Register 3
selects the ramping scheme.
The NLInc sub-register in Noise Control is used to set the ramping speed. When InjCtrl = 1 (such as with the
Advanced NLP), a lower value will give faster ramping. When InjCtrl = 0 (such as with the original NLP), a higher
value will give faster ramping. NLInc is a 4-bit value, so only values from 0 to F(hex) are valid.
NLP Selection
Reject uncanceled echo as noise
Reject double-talk as noise
Noise level estimator ramping scheme
Noise level ramping rate
Noise level scaling
Feature
(dec)
< 1
Table 1 - Comparison of NLP Types
NLPTHR
TSUP = Lrin + 20log
NLPSel (Control Register 3)
NLRun1 (Control Register 3)
NLRun2 (Control Register 3)
InjCtrl (Control Register 3)
NLInc (Noise Control)
Noise Scaling
(hex)
Zarlink Semiconductor Inc.
Register or Bit(s)
= hex(NLPTHR
10
(NLPTHR)
(dec)
* 32768)
NLP Default
Advanced
16(hex)
5(hex)
Value
1
1
1
1
not supported)
not supported)
not supported)
not supported)
Default Value
Original NLP
0 (feature
0 (feature
0 (feature
0 (feature
74(hex)
C(hex)
ZL50234
9