zl50211 Zarlink Semiconductor, zl50211 Datasheet - Page 14

• Manufacturer Part Number: zl50211
• Description: 256 Channel Voice Echo Canceller
• Manufacturer: Zarlink Semiconductor

1.8
Adaptive filters in general do not operate properly when a DC offset is present at any input. To remove the DC
component, each EVP incorporates Offset Null filters in both Rin and Sin inputs.
The offset null filters can be disabled by setting the HPFDis bit to “1” in Control Register 2.
1.9
Each EVP provides adjustable level pads at Rin, Rout, Sin and Sout. This setup allows signal strength to be
adjusted both inside and outside the echo path. Each signal level may be independently scaled with anywhere from
0 to -12 dB level, in 3 dB steps. Level values are set using the Gains register.
CAUTION: Gain adjustment can help interface the ZL50211 to a particular system in order to provide optimum echo
cancellation, but it can also degrade performance if not done carefully. Excessive loss may cause low signal levels
and slow convergence. Exercise great care when adjusting these values.
The -12 dB PAD bit in Control Register 1 is still supported as a legacy feature. Setting this bit will provide 12 dB of
attenuation at Rin, and override the values in the Gains register.
1.10
The ZL50211 has been certified G.168 (1997), (2000) and (2002) compliant in all 64 ms cancellation modes
(i.e. Normal and Back-to-Back configurations) by in-house testing with the DSPG ECT-1 echo canceller tester.
The ZL50211 has also been tested for G.168 compliance and all voice quality tests at AT&T Labs. The ZL50211
was classified as “carrier grade” echo canceller.
2.0
The EVP architecture contains 32 echo cancellers divided into 16 groups. Each group has two echo cancellers
which can be individually controlled (Echo Canceller A (ECA) and Echo Canceller B (ECB). They can be set in
three distinct configurations: Normal, Back-to-Back, and Extended Delay. See Figures 6, 7, and 8.
2.1
In Normal configuration, the two echo cancellers (Echo Canceller A and B) are positioned in parallel, as shown in
Figure 6, providing 64 milliseconds of echo cancellation in two channels simultaneously.
Offset Null Filter
Adjustable Level Pads
Normal Configuration
EVP Configuration
ITU-T G.168 Compliance
Zarlink Semiconductor Inc.
ZL50211
14
Data Sheet