Echo and distortion cancellation arrangement

• US 6,636,605 B1
• Filed: 12/21/1999
• Issued: 10/21/2003
• Est. Priority Date: 12/22/1998
• Status: Expired due to Term

• Current Assignee: Unwired Planet LLC (JP Morgan Chase & Co)
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Randahl, Torbjörn, Barkarö, Stefan
• Primary Examiner(s): BARNIE, REXFORD N
• Application Number:
  US09/468,365
• Time in Patent Office: 1,400 Days
• Field of Search: 379/399.01, 379/400, 379/402, 379/413.02, 379/413.04, 379/414, 379/412, 379/403, 379/398, 379/406.01, 379/406.02, 379/406.03, 379/406.04, 379/406.06, 370/286, 381/94.1
• US Class Current: 379/406.01
• CPC Class Codes: H04B 3/23 using a replica of transmitted signal in the time domain, e.g. echo cancellers

Abstract

At the output of a line driver (1) connected to a long transmission line, signals received on the transmission line are only a fraction of signals transmitted by the line driver on the transmission line. To minimize the transmitted signal with its distortion and noise in the receive path of the line driver, an additional driver (4) having the same voltages and currents in the signal path, is added. The additional driver (4) drives an additional load (Z2). The signal transmitted to the transmission line together with its superimposed received signal, is subtracted from the signal from the additional driver (4), which is not superimposed on any received signal. The resulting signal is reduced from transmitted signal, transmitted distortion and transmitted noise. To minimize die size and power consumption, the additional driver (4) is scaled, but the distortion remains unchanged compared to the “normal” line driver.

Claims

1. An echo and distortion cancellation arrangement for a line driver comprising:

two input terminals;

two output terminals, wherein the output terminals of the line driver are connected to respective wire of a two-wire transmission line as well as to input terminals of receiving means for receiving incoming signals on the transmission line, and wherein the input terminals of the line driver are connected to output terminals of a signal source for generating output signals on the transmission line,

an additional driver having two input terminals and two output terminals, wherein the output terminals of the additional driver are connected to a load as well as to additional input terminals of said receiving means, the input terminals of the additional driver are connected to the output terminals of the signal source for generating signals across the load, and the receiving means subtract the signals generated across the load from the signals appearing on the transmission line to cancel echo, distortion and noise from the incoming signals on the transmission line.

2. The arrangement as claimed in claim 1, wherein the output terminals of the line driver are connected to the respective wire of the two-wire transmission line via terminating impedances

wherein the output terminals of the additional driver are connected to the load via impedances,

wherein the load has an impedance value that is k times the impedance value between the output terminals of the line driver, k being an integer, and

wherein said impedances have an impedance value that is k times the impedance value of the terminating impedances.

3. The arrangement as claimed in claim 1, wherein the input terminals of the line driver are connected to output terminals of a first current-to-voltage converter connected with its input terminals to the wires of the transmission line,

wherein the load has an impedance value that is k times the impedance value between the output terminals of the line driver, k being an integer, and

wherein the input terminals of the additional driver are connected to output terminals of a second current-to-voltage converter connected with its input terminals to the output terminals of the additional driver, the second current-to-voltage converter having a current-to-voltage conversion factor that is k times the current-to-voltage conversion factor of the first current-to-voltage converter.

4. The arrangement as claimed in claim 3, wherein the line driver comprises two first current amplifiers connected with their outputs to the wires of the two-wire transmission line, and connected with one of their inputs to the outputs of the first voltage-to-current converter, the inputs of which being connected to the transmission line, the signal source being connected with its outputs to the other input of the first current amplifiers to generate output signals on the transmission line, wherein the additional driver comprises two second current amplifiers having a current amplification factor that is 1/k times the current amplification factor of the first current amplifiers, connected with their outputs to the load, and connected with one of their inputs to the outputs from the second voltage-to-current converter, the inputs of which being connected to said load, the other inputs of said second current amplifiers being connected to outputs of said signal source for generating the signals across the load.

5. The arrangement as claimed in claim 4, wherein each of the first and the second current amplifiers comprises:

an operational amplifier;

a first resistor connected between the output terminal of the operational amplifier and the output terminal of the current amplifier;

a second resistor connected between the output terminal of the current amplifier and the input terminal of the operational amplifier; and

a third resistor connected between the output terminal of the operational amplifier and the input terminal of the operational amplifier, wherein the resistance of the first resistor in the second current amplifiers is k times the resistance of the first resistor in the first current amplifiers.

6. The arrangement as claimed in claim 1, characterized in that output transistors of the additional driver are 1/k times the size of output transistors of the line driver.