Digital two-to-four wire converter for full duplex signals
AssigneeInternational Telephone and Telegraph Corporation
InventorRobert Treiber
Life of this patent
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Abstract
A digital electronic hybrid circuit for a telephone line circuit is described wherein the two-to-four wire conversion function is provided with an improved synthesized automatic impedance match between the telephone subscriber line and the digital central office. More particularly, an impedance at the input to the line circuit is simulated without the use of discrete components and which closely matches the subscriber line impedance. The circuit digitally separates the full duplex signals on a two-wire transmission path to a pair of digital signals.
Claims17
A circuit for digitally separating full duplex transmit and receive information signals on a two-wire path to a pair of digital signals, each separate from the other, comprising:
- coder means for converting analog transmit and receive signals to a composite digital data stream;
- means for deriving coefficient control data representative of the transmission characteristics of said two-wire path;
- first digital filter means having said transmit signal coupled thereto, and including a coefficient matrix, said transmit signal being multiplied by said coefficient matrix to adjust the digital output of said first digital filter to derive a signal representative of an undesired signal portion from said transmit signal, said coefficient matrix being derived from said coefficient control data, such that a substantially infinite signal return loss is provided between the separated transmit and receive digital signals;
- second digital filter means having said transmit digital signal coupled thereto, and including a variable coefficient matrix controlled by said coefficient control data for providing a synthesized impedance match to said two-wire path;
- decoder means for converting said transmit signal to an analog receive signal, including transconductance amplifier means having a substantially infinite output impedance;
- and
- means for combining said output from said first digital filter with said composite digital data stream to cancel the unwanted return transmit signal from said digital data stream, and having an output consisting of said receive signal.
In a digital two-to-four wire conversion circuit for a telephone subscriber line, the improvement comprising:
- coefficient derivation means including a digital filter for deriving a set of updated digital filter coefficients for said digital filter and related to the subscriber line impedance, said coefficients being derived while said subscriber line is in the OFF-Hook condition, such that said line is terminated in a synthesized matched impedance in said OFF-Hook condition;
- means for comparing said updated digital filter coefficients to a reference to derive an error term;
- means for providing a reduced number of updated filter coefficients for a further digital filter, said further digital filter having a digital return signal coupled thereto for multiplication by said reduced number of filter coefficients to derived a representation of said return signal having opposite polarity from said return signal;
- summation means for combining said representation with a transmission signal including said return signal to eliminate said return signal from said transmission signal;
- and
- decoder means for converting the output of said further digital filter to an analog speech signal.
Dependencies are inferred from the claim text.