Decimator for use with a modem with time invariant echo path

Abstract

Abstract An ISDN modem. The modem includes an independent clock which controls the modem's input and output filters and two dependent clocks whose rates are functions of the independent clock and which are synchronized with external timing signals. When a dependent clock is synchronized, timing adjustment signals to other components of the modem specify the type and direction of synchronization. One of the dependent clocks and the independent clock are used to control a decimator which provides two samples of a symbol which are one independent clock cycle apart. The decimator, in conjunction with other elements, employs low frequency filters in selectively providing time-invariant samples. Advantageously, the use of low frequency filters reduces the overall circuit complexity and power consumption of the decimator. One of the samples is a primary sample from which the symbol is interpreted and the other is a secondary sample which is used to continually train a jitter canceller. When a clock is synchronized, the secondary sample becomes the primary sample, providing the modem with a time-invariant echo path. On clock synchronization, the jitter canceller responds to the timing adjustment signals by providing adaptation information to the linear echo canceller.

Inventors

• 👤 Oscar Ernesto Agazzi

Bibliographic Details