Zarlink voice echo canceller eases design of converged network equipment

The rapid growth of VoIP (voice-over-IP) services is driving demand for a new class of telecom 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.

The ZL38015 voice processing platform is built on a voice optimized 100 MHz (200 effective MIPS) DSP with an integrated 1024 tap filter co-processor, 16 KW instruction and 8 KB data memory, hardware accelerators, SPI (serial peripheral interface), UART (universal asynchronous receiver/transmitter) and TDM (time division multiplexing) interfaces, multiprotocol TDM ports, flexible clocking scheme support and 10 GPIOs (general purpose input/outputs).

The ZLS38233 is a four-channel VEC with echo tail programmable up to 64 ms 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 ms to 64 ms without compromise.

The ZLS38233 firmware also integrates a range of features to support superior voice quality. A highly flexible DTMF (dual-tone multi-frequency) transmit programmable tone generator can generate dual DTMF or single tones, with burst mode support from zero to four seconds and programmable output gains from –18 db to 24 db in 6 db steps to allow for the generation of DTMF, CNG (comfort noise generator), central office and other telecom signaling functions. An integrated four-channel DTMF receiver detects standard dual tone DTMF tones, and accepts a minimum tone duration on 40 ms. The DTMF Rx supports sensitivity of greater than –37 dbm and accept and reject of less than –5 dbm.

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

The ZLS38233 builds on Zarlink’s extensive portfolio of VEC devices with capabilities that exceed ITU-T G.168 requirements, including double-talk, and advanced NLP (non-linear processor) and echo cancellation performance.

Availability and packaging

Zarlink’s ZL38015 VEC with integrated ZLS38233 firmware is in volume production. The device is offered as a lead-free 100-pin QFP (quad flat package) measuring 14 mm x 14 mm. For information, please visit http://products.zarlink.com/product_profiles/ZL38015.htm.