Electronic Design

Embedded Speech Processor Eases Voice-Activated Dialing

The ADSP-21ESP202 embedded speech processor targets full-duplex hands-free cellular communication in an vehicles. A wide variety of features lets it act as a single-chip solution for other applications as well.

The processor is derived from the 50-MIPS ADSP-218x programmable 16-bit fixed-point DSP core. It includes dual voice-band 16-bit codecs and dual high-speed comparators. Two current switch outputs, 40 kbytes of on-chip RAM, and 8 kwords of program ROM are packed onto the device. So are a byte DMA controller, a 16-bit internal DMA port, high-speed serial ports, enhanced timers, and extensive interrupt abilities.

DSP product manager Ken Waurin says that the ADSP-21ESP202 also offers sufficient memory for code to reside on the chip. The 8 kwords or 24 kbytes of on-board ROM provide the differentiating code. With sufficient ROM, the processor can be programmed with standard functions or customer-defined features for differentiation.

To permit both instruction and data storage on-chip, the 40-kbyte RAM is configured as 8 kwords (24 bits) of program memory and 8 kwords (16 bits) of data RAM. The three-bus architecture allows dual-operand fetches in every instruction cycle, enabling single-cycle instruction execution. The instruction cycle time is 20.3 ns. It provides the option of using the internal DMA port for fast access to on-chip memory or a byte DMA controller for accessing memory off-chip.

With the internal DMA port, the user can download code from an external processor. Likewise, the byte DMA controller gives the DSP access to an external nonvolatile memory. Meanwhile, the voice-band codecs employ delta-sigma technology to support a sampling rate up to 64 ksamples/s. It also provides a 75-dB signal-to-noise ratio for the analog-to-digital converter and a 70-dB SNR for the digital-to-analog converter. Furthermore, it supplies programmable input gain and output attenuation.

Implemented in a 0.35-µm triple metal layer CMOS process, the speech processor operates at 3.3 V with 5-V tolerant I/O. Since this part was still being characterized at press time, the power consumption for the device was unavailable. However, the typical consumption for the ADSP-218x DSP core is about 160 mW at 3.3 V. It comes in a 128-lead LQFP package. While the speaker-dependent software for hands-free applications is available now, the code for continuous speech recognition is expected in the fourth quarter.

In 1000-piece quantities, the ADSP-21ESP202 costs $15.95.

Analog Devices Inc., One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106; (800) 262-5643; Internet: www.analog.com.

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