Modeling and calibrating a three-port time-domain reflectometry system
A three-port TDR front end comprises numerous components. An exemplary three-port TDR front end is a DSL modem. Information-bearing TDR signals are distorted as they pass through these components. With a perfect model of the response of its front-end, a TDR system usually can compensate for the effects of its front-end. In reality, however, the electrical characteristics of each component vary from design-to-design, board-to-board, and slowly over time. The result is imperfect knowledge about the true response of the front-end, errors in the model of the front-end, and degraded TDR performance. At least for this reason it is important to precisely calibrate the response of the TDR front-end through the use of a TDR modeling system.
1 . A method of predicting the response of a linear, time-invariant system comprising:
determining at least three system responses when a third port is connected to each of at least three different devices, wherein the electrical characteristics of the at least three devices are known;
determining three parameters that characterize a front-end; and
using the three parameters to predict the system response when the front-end is connected to any device.
2 . The method of claim 1 , wherein the devices are linear, time-invariant one-port electrical networks.
3 . The method of claim 1 , wherein the three parameters model a three-port time domain reflectometry front-end.
4 . The method of claim 3 , wherein the front-end model accounts for any linear, time-invariant implementation.
5 . A method of calibrating a DSL transceiver front-end for operation as a TDR system, the method comprising:
determining three independent parameters that characterize the DSL transceiver front-end.
6 . The method of claim 5 , wherein three different predetermined impedances are utilized to determine three echo responses.
7 . The method of claim 6 , further comprising:
connecting additional predetermined impedances to the DSL transceiver front-end; and
transmitting a waveform and receiving an echo response in the DSL transceiver for each of the additional predetermined impedances.