Innovative Solutions for the emerging LAN/WAN & Broadband Markets

  1394 Transceiver  USB 2.0 USB2.0 PHY UTMI

Data Communication involves conveying information by transmitting successive choices from a finite alphabet over a band-limited channel, with usually frequency selective distortion and various forms of noise. Another major issue which needs to be resolved with data communications is Carrier and  Clock Recovery. Soft Mixed Signal Corporation focuses on the Physical Layer products which require design and implementation of foundation technologies such as Modulation/Demodulation, Equalization, Cancellation of known disturbances, Coding/Decoding, and Synchronization.

Modulation:

    Before passing Digital Data to the transmission medium, the Base-Band  Data Signals need to be converted to Pass-Band by Modulators. At the receiver, the effects of Modulation are reversed by using Demodulators. Main methods of Modulation are FSK (Frequency Shift Keying), PSK (Phase Shift Keying), CAP (Carrierless Amplitude/Phase Modulation) and, QAM (Quadrature Amplitude Modulation). For Base-Band Channels (such as Twisted Pair channels used in 10Base-T and 100Base-TX) PAM (Pulse Amplitude Modulation) is widely used.

Synchronization:

    Digital Communication requires synchronization of receiver actions to the transmitter. For Coherent Communications of Pass-Band Signals Carrier Synchronization is necessary. For correct sampling of received data, Timing Synchronization (or recovery) is used. Timing recovery is also called Clock Recovery.

Channel Equalization:

    One of the largest impairments in most Wired Channels is ISI (Inter Symbol Interference). ISI is introduced by Linear Distortion in the Communication Channel. To combat ISI an Equalizer is used to translate received symbols into something similar to what has been transmitted. If the channel is known, a fixed Equalizer is used but mostly Adaptive Equalizers are needed because the channels vary between installations and over time (albeit slowly for wired channels). Adaptive Equalizers usually use LMS (Least Mean Square) as their adaptation technique.

NEXT and Echo Cancellation:

    NEXT (Near End Crosstalk) and Echo Cancellation can be used to enhance the SNR (Signal to Noise Ratio) of the Channel when needed. NEXT occurs when the transmitted signal couples to the wired channel used for reception. Because the Transmitted Signal is known, a large portion of NEXT can be cancelled at the receiver. Echo is caused by the Hybrid Devices which are used to transmit and receive at the same time using a single pair of wire or in Duplex Mode. Because the impedance matching of the Hybrid is not Perfect, some of the transmitted signal reflects to the receive path.

Copyright 2003 by Soft Mixed Signal Corporation

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