Texas Instruments (TI) announced a mixed-signal voice coding-decoding device (codec) designed for use in Code Division Multiple Access-based (CDMA) wireless handset applications. The new voice-band audio processor (VBAP) provides designers with greater programming flexibility and ease of design, while at the same time improving system voice quality and reducing power consumption.

"TI pioneered voice codecs with its original VBAP products," said Gilles Delfassy, worldwide director of the Texas Instruments Wireless Communications Business Unit and TI vice president. "Now the TWL1101 Voice-Band Audio Processor enhances TI's leadership in wireless analog/mixed-signal technology with features that make the device more widely applicable and provide more system-level control through programming."

A Next-Generation Voice Codec

The TWL1101 is an enhancement of TI's existing family of VBAP products, which are used extensively in wireless cellular and personal communications systems (PCS) phones, as well as in many other applications. Like the earlier VBAPs, the TWL1101 performs the transmit encoding (analog-to-digital conversion) and receive decoding (digital-to-analog conversion) and provides transmit and receive filtering for wireless phones and other voice-band communications systems.

In addition to supporting CDMA systems, the device is also compatible with any other type of application requiring an interface between a human voice and a digital signal processor (DSP) or microcontroller. Systems that can benefit include hands-free cellular kits, speakerphones, answering machines, voice modems, digital intercoms, digital public exchanges (PBXs), wireless local loop handsets, voice interfaces to computers, and voice-activated security systems.

Among the TWL1101 enhancements are Sigma-Delta technology and digital filtering, which require less power and produce a higher-quality voice signal compared to earlier codecs. Added sidetone produces a more natural voice sound from the speaker and also simplifies DSP programming by offloading sidetone algorithms. To simplify system clocking, the device generates all necessary internal clocks.

All the new features of the TWL1101 VBAP are fully programmable through the I²C Busı serial interface. This programmability gives designers added flexibility for controlling all channeling, filter response and bi-directional gain settings and allows selection between 13-bit linear or 8-bit ı-law companded data mode. Two selectable microphone inputs and two selectable speaker outputs ease the implementation of after-market car kits.

"The announcement of the TWL1101, coupled with TIıs new LinEPIC III process technology, establishes a solid foundation for TI to provide an analog/mixed-signal roadmap for third-generation wireless communication systems," concluded Delfassy.

There is little that annoys this Editor more than marketing "throwaways." The big one with this product announcement is in the last line linking the product with TI's new LinEPIC III process (see Technology Diary entry for August 31, 1998 on Analog Avenue), offering the illusion that this product is manufactured in that process. It is not, it is manufactured in the earlier LinEPIC II process. I also had a real hard time understanding the basics of what TI was trying to achieve with this product until I was able to actually go through the engineering data and see what some of the cute marketing material was not letting me see (and indeed misleading me in a couple of places.)

This is actually a great step-forward product but instead of thinking of it as just a codec think of its as a voice/PCM codec. The provisions of two microphone inputs and two earphone outputs (one single-ended without crackle/pop protection) are for after-market mounting in hands-off vehicle operations, while the gain controls are extensive. The input microphone (switched between one or the other) can have a fixed gain of either 2.6 or 5.4 dB and a further PGA in the chain after digitizing provides for 2-dB step gains over 6 dB. On the receive channel 18 dB of gain is provided (in 2-dB steps) before conversion back to analog and the earphone channels have 12 dB gain variation in 1 dB steps. There are ample opportunities to go off-chip for special gain and filtering. Sidetone cancellation is also provided, programmable and variable over 12 dB, or mute. I don't understand TI's strange use of terminology such as "Analog Modulator" when talking about the analog-to-digital conversion in the transmit channel, and "Digital Modulator" when talking about the digital-to-analog conversion in the receive channel.

This part will be a major success for uses other than just CDMA work. The numbers are right, the specs are right, the power conditions are right, and the price is right. The TWL1101 is in a 48-lead TQFP and will also be offered in a BGA later in the year; it is priced at $3.45 in 1000-piece lots and is in production.