Electronic Design

Voice Chips Reinvent Telephony Architecture

Existing plain-old-telephone-service/public-switched-telephone-network systems are patchworks of hardware designed for centralized circuit-switch functionality and four to 16 channels. But the industry is slowly changing to packet-centric systems that feature decentralized, multifunction hardware with one to 64 channels. The VoiceEdge architecture is at the forefront of this evolution.

This line of 20 chips from Legerity essentially reinvents the telephony infrastructure for packet-based technology (see the figure). The VE790 analog line interface chips focus on carrier applications like central office, DSL access multiplexer (DSLAM), and digital loop carrier. The VE880 VoicePort series targets network-edge equipment on the customer's premises.

Traditional architectures require separate circuits for packet processing, voice processing (DSP), subscriber-line audio-processing circuit (SLAC), and subscriber-line interface circuit (SLIC). The VE790 chips integrate the voice processing and SLAC functions in a single device, greatly simplifying design, speeding time-to-market, increasing board density, and reducing costs. The chips' fully integrated testing eliminates the need for the external, expensive test heads used in mid- to high-line-count systems.

Service providers can now solve most customer problems from the office by executing remote line-test measurements. This eliminates costly truck rolls and shortens response time to the customer, which dramatically reduces costs. According to Legerity, the VE790 sets are the first chips ever to integrate all of the functionality required to control and manage multiple telephone lines on a single line card.

The chip set handles ring sequencing, caller ID sequencing, call progress tone, and other functions, reducing the design effort to add voice to DSLAM systems. The VE790 series includes the Le79112 Digital Voice Processor, the Le79610 PacketSLAC, several dual SLACs, and an octal SLAC.

Legerity also claims that the VE880 VoicePort chips are the world's first single-device telephone-line interfaces to implement all BORSCHT functions from the high-voltage subscriber-line interface to the embedded micro interface. The VE880 series makes adding voice to broadband access equipment cheaper and easier. It should help speed voice-over-IP implementation and usage as well.

The fully software-programmable chips implement a highly functional line interface that meets the requirements of short, medium, and long loop applications. Key features include a high-voltage switching regulator, self test, line-test capability, integrated ringing (up to 140 V p-p), a flexible signal generator with tone cadencing, caller ID generation, and all BORSCHT functions.

The VE880 series promises to simplify design, lower component count, and provide the smallest footprint available. The Le88111, Le88311, and Le88211 are single-, one-and-a-half-, and two-channel devices, respectively. The Le88010/020 is the VoicePort codec.

The VE880 costs $2.50 per channel, and the VE790 costs $3.00 per line, both in high volume.

Legerity Inc.
(512) 288-5760

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