ZL38001 参数 Datasheet PDF下载

ZL38001

1.3

Narrow Band Signal Detector (NBSD)

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Data Sheet

Single or multi-frequency tones (e.g,. DTMF, or signalling tones) present in the reference input of an echo canceller

for a prolonged period of time may cause the adaptive filter to diverge. The Narrow Band Signal Detector (NBSD) is

designed to prevent this divergence by detecting single or multi-tones of arbitrary frequency, phase, and amplitude.

When narrow band signals are detected, the filter adaptation process is stopped but the echo canceller continues to

cancel echo.

The NBSD can be disabled by setting the NB- bit to 1 in the MC control registers.

1.4

Howling Detector (HWLD)

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The Howling detector is part of an Anti-Howling control, designed to prevent oscillation as a result of positive

feedback in the audio paths.

The HWLD can be disabled by setting the AH- bit to 1 in the (MC) control register.

1.5

Offset Null Filter

To ensure robust performance of the adaptive filters at all times, any DC offset that may be present on either the

Rin signal or the Sin signal, is removed by highpass filters. These filters have a corner frequency placed at 40 Hz.

The offset null filters can be disabled by setting the HPF- bit to 1 in the AEC control registers.

1.6

Limiters

To prevent clipping in the echo paths, two limiters with variable thresholds are provided at the outputs.

The Rout limiter threshold is in Rout Limiter Register 1 and 2. The Sout limiter threshold is in Sout Limiter Register.

Both output limiters are always enabled.

1.7

User Gain

The user gain function provides the ability for users to adjust the audio gain in the receive path (speaker path). This

gain is adjustable from -24 dB to +48 dB in 3 dB steps. It is important to use ONLY this user gain function to adjust

the speaker volume. The user gain function in the ZL38001 is optimally placed between the two echo cancellers

such that no reconvergence is necessary after gain changes.

The gain can be accessed through Receive Gain Control Register.

1. Patent Pending

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Zarlink Semiconductor Inc.