ZL38001 Data Sheet
10
Zarlink Semiconductor Inc.
1.0 Changes Summary
The following table captures the changes from the October 2006 issue.
2.0 Functional Description
The ZL38001 device contains an acoustic echo cancellers, as well as the many control functions necessary to
operate the echo canceller. The ZL38001 provides clear signal transmission in both audio path directions to ensure
reliable voice communication, even with low level signals. The ZL38001 does not use variable attenuators during
double-talk or single-talk periods of speech, as do many other acoustic echo cancellers for speakerphones.
Instead, the ZL38001 provides high performance full-duplex operation similar to network echo cancellers, so that
users experience clear speech and uninterrupted background signals during the conversation. This prevents
subjective sound quality problems associated with “noise gating” or “noise contrasting”.
The ZL38001 uses an advanced adaptive filter algorithm that is double-talk stable, which means that convergence
takes place even while both parties are talking
1
. This algorithm allows continual tracking of changes in the echo
path, regardless of double-talk, as long as a reference signal is available for the echo canceller.
The echo tail cancellation capability of the acoustic echo canceller has been sized appropriately (112 ms) to cancel
echo in an average sized office with a reverberation time of less than 112 ms.
In addition to the echo cancellers, the following functions are supported:
• Control of adaptive filter convergence speed during periods of double-talk, far end single-talk and near-end
echo path changes
• Control of Non-Linear Processor thresholds for suppression of residual non-linear echo
• Howling detector to identify when instability is starting to occur and to take action to prevent oscillation
• Narrow-Band Detector for preventing adaptive filter divergence caused by narrow-band signals
• Offset Nulling filters for removal of DC components in PCM channels
• Limiters that introduce controlled saturation levels
• Serial controller interface compatible with Motorola, National and Intel microcontrollers
• PCM encoder/decodercompatible with/A-Law ITU-T G.711, /A-Law Sign-Mag or linear 2’s complement
coding
• Automatic gain control on the receive speaker path
2.1 Adaptation Speed Control
The adaptation speed of the acoustic echo canceller is designed to optimize the convergence speed versus
divergence caused by interfering near-end signals. Adaptation speed algorithm takes into account many different
Page Item Change
1 Ordering Information Box Removed the ZL38001QDC and ZL38001DGA packages.
3 “Pin Description“ Table Removed QSOP Pin Descriptions.
3 “Pin Description“ Table Added SSOP Pin Descriptions.
46 QSOP Package Outline Removed mechanical drawing of the QSOP package.
46 SSOP Package Outline Added mechanical drawing of the SSOP package.
1. Patent pending.
