TMS320WP010

DIGITAL SIGNAL PROCESSOR

FOR AEC/LEC/ANS

SPRS040–OCTOBER 1995

1

POST OFFICE BOX 655303

Hands-Free Use of Cellular Phones in

Automobiles

– Eliminates Echo Created by Speaker

Output Feeding Back Into the

Microphone

– IS-54B, IS-136, GSM, AMPS, IS-95

Changing Acoustic Environment

– Initial System Training Not Required

Microcontrollers

TCM320AC36

– Length of Echo Path up to 44 ms

– Initial Adaptation Rate

>20 dB/s for

Speech Signals

– Zero Speech Delay

– Echo Return Loss up to 30 dB for

Speech Echo in Automobiles and 41 dB

for Sine Wave Input

– Up to 10 dB Noise Suppression for

Hands-Free Use of Cellular Phones in

Automobiles Without Distorting Speech

Signals

– 16 ms Processing Delay

– Continuous Adaptation

– Allows Evaluation of Software Algorithm

Performance in Lab and Automobile

– Ability to Enable/Disable AEC, ANS, and

LEC

description

For the cellular phone cradle market, the TMS320WP010 provides enhanced quality, full-duplex, hands-free

communications. The ’WP010 is a ROM-coded DSP that provides all the adaptive filtering and processing

necessary for acoustic echo cancellation (AEC), line echo cancellation (LEC), and adaptive noise suppression

(ANS).

The ’WP010’s acoustic echo cancellation function is based on a Finite Impulse Response (FIR) filter with an

adaptive coefficient updating algorithm. The adaptive algorithm updates continuously so that it can constantly

track acoustic path changes from the speaker to the microphone. Based upon FIR filter coefficients, the echo

signal can be estimated and subtracted from the observed signal at the microphone. The acoustic echo

cancellation function provides continuous adaptation and needs no initial system training. It is capable of

canceling an echo path of up to 44 milliseconds and provides up to 30 dB cancellation for speech signals. In

addition, the initial convergence rate is faster than 20 dB per second.

The line echo cancellation function cancels the near-end speech that has been reflected at the network switch

and transmitted back to the cellular phone. The principle of the line echo cancellation function is very similar

to that of the acoustic echo cancellation function. The difference is that the line echo cancellation function is

designed to cancel the echo signal caused by network feedback due to impedance mismatch in the network

circuit. The line echo cancellation function is capable of canceling a line echo path of up to 16 milliseconds.

The received signal at the microphone consists of the near-end speech signal, acoustic feedback echo, and

ambient noise from the environment. The purpose of the adaptive noise suppression function is to suppress

ambient noise components without distorting near-end speech. The initial adaptation rate is about 3 dB per

second without initial system training. It tracks the changes of the noise characteristics and suppresses noise

accordingly. The adaptive noise suppression provides up to 10 dB of noise cancellation without degrading

near-end speech.

Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of

Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.

PRODUCTION DATA information is current as of publication date.

Products conform to specifications per the terms of Texas Instruments

standard warranty. Production processing does not necessarily include

testing of all parameters.

Copyright

© 1995, Texas Instruments Incorporated