Scaled impedance replica for echo attenuation in digital transmission systems

Abstract

A device for echo attenuation in a digital transmission system comprises an impedance replica of the transmission path, wherein the impedance replica consists of a terminating resistor replica, a transformer replica and a transmission line replica. Further the device can comprise an additional bridged tap replica. The transformer replica and the bridged tap replica are located on chip and the main transformer inductance replica and all components of the bridged tap replica are made variable so that a software setting is possible.

Description

background of the invention

[0001] In a semiconductor-based digital transmission system, such as ISDN or XDSL, sending and receiving signals are performed on the same pair of metal wires from location A to B. As long as no special precautions are taken. The received signal, referred to below as the far-end signal, is overlaid by the own transmitter's signal, referred to as the echo, which brings about two disadvantages:

[0002] a) The receive path input must be designed with a high input level. The possible signal-to-noise ratio (S / N) is thus limited.

[0003] b) In common ISDN and XDSL transmission systems you can find digital linear echo compensators after the analog receive path. Such echo compensators are not capable of subtracting nonlinear distortion components from the echo. Thus the signal-to-distortion ratio (S / D) must be kept very low.

[0004] To overcome the above-mentioned problems, a proportional impedance replica of the transmission path consisting of resi...

Examples

Embodiment Construction

[0015] The receiver / transmitter chip (surrounded by thick lines) includes the line driver LD for driving the connector and ring signal lines TTIP and TRING. The signal received from the loop by the receiver / transmitter chip RTC is connected to the chip through the signal lines RTIP and RRING connected to the termination resistor R, the connector in front of R and the ring line TTIP, TRING. The received signal is sent to a part AGC of the chip TRC which acts as a subtractor.

[0016] Since the received far-end signal is superimposed by the echo signal generated by signal propagation through the line driver LD, the echo signal must be removed. This is accomplished by generating artificial or replica echo signals and subtracting them from the sum of the received far-end signal and the echo signal. Impedance replicas include a replica transmit tap line RTTIP and a replica transmit loop line RTRING connected to a transformer replica, a bridge tap replica and a signal loop replica ...

background of the invention

[0001] In a semiconductor-based digital transmission system, such as ISDN or XDSL, sending and receiving signals are performed on the same pair of metal wires from location A to B. As long as no special precautions are taken. The received signal, referred to below as the far-end signal, is overlaid by the own transmitter's signal, referred to as the echo, which brings about two disadvantages:

[0002] a) The receive path input must be designed with a high input level. The possible signal-to-noise ratio (S / N) is thus limited.

[0003] b) In common ISDN and XDSL transmission systems you can find digital linear echo compensators after the analog receive path. Such echo compensators are not capable of subtracting nonlinear distortion components from the echo. Thus the signal-to-distortion ratio (S / D) must be kept very low.

[0004] To overcome the above-mentioned problems, a proportional impedance replica of the transmission path consisting of resi...

Examples

Embodiment Construction

[0015] The receiver / transmitter chip (surrounded by thick lines) includes the line driver LD for driving the connector and ring signal lines TTIP and TRING. The signal received from the loop by the receiver / transmitter chip RTC is connected to the chip through the signal lines RTIP and RRING connected to the termination resistor R, the connector in front of R and the ring line TTIP, TRING. The received signal is sent to a part AGC of the chip TRC which acts as a subtractor.

[0016] Since the received far-end signal is superimposed by the echo signal generated by signal propagation through the line driver LD, the echo signal must be removed. This is accomplished by generating artificial or replica echo signals and subtracting them from the sum of the received far-end signal and the echo signal. Impedance replicas include a replica transmit tap line RTTIP and a replica transmit loop line RTRING connected to a transformer replica, a bridge tap replica and a signal loop replica ...

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