Canceller copes with complex echo issues

Echo canceller combines hardware and firmware to provide superior voice performance across converging networks.

Zarlink Semiconductor has expanded its voice echo canceller product portfolio with a hardware and firmware platform for next-generation telecomms equipment that support voice services over converging networks.

The highly integrated ZL38015 hardware and ZLS38233 firmware solution helps manufacturers simplify design, reduce time to market and lower bill-of-material and resource costs.

The rapid growth of VoIP services is driving demand for a new class of telecomms equipment that ensures superior voice performance across converging networks.

For example, enterprise media gateways, VoIP phone sets and IADs (integrated access devices) must seamlessly handle voice traffic across circuit and packet networks, with no discernable loss in quality for the end-user.

"Converging voice networks present a challenge for conventional VECs, which must handle complex echo issues that may be further emphasised by the longer signal processing and transmission delays associated with packet infrastructures", says Jarrod Thorne, Product Marketing Manager of Zarlink's Telecom Networking portfolio.

"The ZL38015 hardware and ZLS38233 firmware supports full-band echo cancellation and advanced algorithms while offloading the heavy MIPs consuming VEC and DTMF functions from the main processor".

"Compared with competing solutions that require significant integration resources, Zarlink's VEC platform is a drop-in solution that simplifies design and ensures high-quality voice with field-upgradeable firmware to easily support future applications".

The ZL38015 voice processing platform is built on a voice optimised 100MHz (200MIPS effective) DSP with an integrated 1024 tap filter coprocessor, 16Kword instruction and 8Kbyte data memory, hardware accelerators, SPI, UART and TDM interfaces, multiprotocol TDM ports, flexible clocking scheme support and 10 general-purpose I/Os.

The ZLS38233 is a four-channel VEC with echo tail programmable up to 64ms per channel.

Where competing solutions will often employ windowing algorithms in the DSP to locate and cancel peaks in echo profiles, the ZLS38233 VEC supports full band echo cancellation.

Windowing algorithms may not detect multiple echo paths in a signal, resulting in incomplete echo cancellation.

In addition, echo tails outside the windowing algorithm may not be cancelled.

In comparison, the ZLS38233 VEC eliminates echo from 0 to 64ms without compromise.

The ZLS38233 firmware also integrates a range of features to support superior voice quality.

A highly flexible DTMF transmit programmable tone generator can generate dual DTMF or single tones, with burst mode support from 0 to 4s and programmable output gains from -18 to 24dB in 6dB steps to allow for the generation of DTMF, CNG (comfort noise generator), central office and other telecomms signalling functions.

An integrated four-channel DTMF receiver detects standard dual tone DTMF tones, and accepts a minimum tone duration on 40ms.

The DTMF Rx supports sensitivity of greater than -37dBm and accept and reject of less than -5dBm.

All four channels of the ZLS38233 support G.169 automatic level control to help maintain a stable voice connection and prevent instability in the echo path through a programmable gain range from 0 to -24 to 24dB.

The ZLS38233 builds on Zarlink's extensive portfolio of voice echo canceller devices with capabilities that exceed ITU-T G.168 requirements, including double-talk, and advanced nonlinear processor and echo cancellation performance.

Zarlink's ZL38015 voice echo canceller with integrated ZLS38233 firmware is in volume production.

The device is offered as a lead-free 100-pin QFP (quad flat package) measuring 14mm square.

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