Single-ended loop test circuitry in a central office DSL modem

Details Single-ended loop test circuitry in a central office DSL modem Single-ended loop test circuitry in a central office DSL modem

2006-04-11

2006-04-11

Tran, Sinh (Department: 2646)

Telephonic communications

Subscriber line or transmission line interface

C379S399020, C379S402000, C379S345000, C379S026010, C379S026020, C379S027010, C379S027060, C379S029010

Reexamination Certificate

active

07027589

ABSTRACT:
A central office modem (50) that includes the capability of single-ended loop testing (SELT) is disclosed. The modem (50) includes a digital signal processor (54), a codec (56), line driver and receiver circuitry (58), and a hybrid circuit (60), by way of which a subscriber loop (LOOP) can be driven and sensed. The line driver and receiver circuitry (58) may include a transformer (74a,74b) for driving the loop (LOOP), or the output may be capacitively coupled. The line driver and receiver circuitry (58) includes active termination, by way of operational amplifiers (80a,80b). Switches (82a,82b;84a,84b) are provided to selectively enable and disable the active termination function, and to selectively bypass or include the hybrid circuit (60). This control of the line driver and receiver circuitry (58) provides the ability to calibrate out its own characteristics, providing high precision SELT measurements of the load impedance type, and of frequency domain reflectometry, and time domain reflectometry. A third set of switches (86a,86b) selectively bypass receive path filter circuitry (78), to permit upstream and downstream noise measurements.

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Bostoen, et al., “Estimation of the Transfer Function of a Subscriber Loop by Means of a One-Port Scattering Parameter Measurement at the Central Office”,J. Selected Areas in Communications, vol. 20, No. 5 (IEEE, Jun. 2002), pp. 936-948.
Galli, et al., “Loop Makeup Identification Via Single Ended Testing: Beyond Mere Loop Qualification”,J. Selected Areas in Communications, vol. 20, No. 5 (IEEE, Jun. 2002), pp. 923-935.

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