DSP应用与实例2 .pdf

DSP APPLICATIONS SECTION 9 DSP APPLICATIONS High Performance Modems for Plain Old Telephone Service (POTS) Remote Access Server (RAS) Modems ADSL (Assymetric Digital Subscriber Line) Digital Cellular Telephones GSM Handset Using SoftFone™ Baseband Processor and Othello™ Radio Analog Cellular Basestations Digital Cellular Basestations Motor Control Codecs and DSPs in Voiceband and Audio Applications A Sigma-Delta ADC with Programmable Digital Filter 9.a DSP APPLICATIONS 9.b DSP APPLICATIONS SECTION 9 DSP APPLICATIONS Walt Kester HIGH PERFORMANCE MODEMS FOR PLAIN OLD TELEPHONE SERVICE (POTS) Modems (Modulator/Demodulator) are widely used to transmit and receive digital data using analog modulation over the Plain Old Telephone Service (POTS) network as well as private lines. Although the data to be transmitted is digital, the telephone channel is designed to carry voice signals having a bandwidth of approximately 300 to 3300Hz. The telephone transmission channel suffers from delay distortion, noise, crosstalk, impedance mismatches, near-end and far-end echoes, and other imperfections. While certain levels of these signal degradations are perfectly acceptable for voice communication, they can cause high error rates in digital data transmission. The fundamental purpose of the transmitter portion of the modem is to prepare the digital data for transmission over the analog voice line. The purpose of the receiver portion of the modem is to receive the signal which contains the analog representation of the data , and reconstruct the original digital data at an acceptable error rate. High performance modems make use