US 6,226,322 B1 · Analog receive equalizer for digital-subscriber-line communications system

Abstract

Digital subscriber modems (8, 15) for use in Asynchronous Digital Subscriber Line (ADSL) communications are disclosed. Each modem includes a digital transceiver function (10, 13) and an analog front end function (10, 11), where the analog front end function (10, 11) is integrated into a single integrated circuit. According to the disclosed embodiments, the analog front end functions (10, 11) each include a transmit and a receive side. The transmit side includes oversampled registers (44C, 44R) and digital filters (46C, 46R) which serve to increase the sample rates of the digital data to be transmitted, so that the analog-to-digital converter (48C, 48R) operates in an oversampled manner, and so that the downstream analog low pass filters (50C, 50R) can be realized with relatively simple, low-order filters. On the receive side, digital filter functions (64C, 64R) are included downstream from the analog-to-digital converters (62C, 62R), to minimize the complexity of the receive-side analog filters (58C, 58R). The remote DSL modem (8) also includes an equalizer function (57) to boost the signal amplitude with increasing frequency, to overcome the effects of line attenuation on the high frequency downstream transmissions.

Claims27

Dependent claims

A receive equalizer circuit, comprising:

a first stage, comprising:
a first operational amplifier, having an input and an output;
a first input impedance network, coupled between an input of the receive equalizer circuit and the input of the first operational amplifier, having an impedance selected from one of a first plurality of input impedance values to define a first dominant zero in a frequency characteristic of the receive equalizer circuit, and comprised of a capacitor and a variable resistance connected in parallel with the capacitor;
and
a first feedback impedance network, coupled between the output and the input of the first operational amplifier, and having an impedance selected from one of a first plurality of feedback impedance values and that is comprised of a capacitor and a variable resistance connected in parallel with the capacitor;
and
a second stage, comprising:
a second operational amplifier, having an input, and an output;
a second input impedance network, coupled between the output of the first operational amplifier and the input of the second operational amplifier, to define a second dominant zero in the frequency characteristic of the receive equalizer circuit;
and
a second feedback impedance network, coupled between the output and the input of the second operational amplifier;
wherein each of the variable resistances comprise a plurality of resistors connected in parallel with one another, each of the plurality of resistors capable of being selectably enabled and disabled.

9 more elements

A receive equalizer circuit, comprising:

a first stage, comprising:
a first operational amplifier having a non-inverting input and an inverting input, and a non-inverting output and an inverting output;
a first input impedance network, coupled between a first input of the receive equalizer circuit and the inverting input of the first operational amplifier, and having an impedance selected from one of a first plurality of input impedance values;
and
a first feedback impedance network coupled between the non-inverting output and the inverting input of the first operational amplifier, and having an impedance selected from one of a first plurality of feedback impedance values;
and
a second stage, comprising:
a second operational amplifier, having an input, and an output;
a second input impedance network, coupled between the output of the first operational amplifier and the input of the second operational amplifier;
and
a second feedback impedance network, coupled between the output and the input of the second operational amplifier;
a third input impedance network, coupled between a second input of the receive equalizer circuit and the noninverting input of the first operational amplifier, and having an impedance selected from one of a third plurality of input impedance values;
and
a third feedback impedance network, coupled between the inverting output and the noninverting input of the first operational amplifier, and having an impedance selected from one of a third plurality of input impedance values.

11 more elements

An analog front end circuit for a modem, integrated into a single integrated circuit, and comprising:

a digital interface, for communication of digital signals;
a digital-to-analog converter, coupled to the digital interface, for converting digital signals received from the digital interface into analog signals;
a transmit filter, for filtering the analog signals into a first transmit frequency band;
a receive equalizer for amplifymg the received analog signals according to a frequency response, comprising:
a first stage, comprising:
a first operational amplifier, having an input and an output;
a first input impedance network, for applying received analog signals, in a first receive frequency band, to the input of the first operational amplifier, and having an impedance selected from one of a first plurality of input impedance values;
and
a first feedback impedance network, coupled between the output and the input of the first operational amplifier, and having an impedance selected from one of a first plurality of feedback impedance values;
and
a second stage, comprising:
a second operational amplifier, having an input, and an output;
a second input impedance network, coupled between the output of the first operational amplifier and the input of the second operational amplifier;
and
a second feedback impedance network, coupled between the output and the input of the second operational amplifier;
an analog-to-digital converter, coupled to the receive analog filter, for converting the filtered analog signals into digital signals;
and
a receive digital filter, coupled to the analog-to-digital converter, for applying a digital filter function to the converted digital signals, and having an output coupled to the digital interface.

15 more elements

A digital subscriber line modem, comprising:

a host interface;
a digital transceiver function coupled to the host interface;
an analog line driver, for driving and receiving analog signals over a telephone facility;
and
an analog front end circuit, integrated into a single integrated circuit, and comprising:
a digital interface, for communication of digital signals;
a digital-to-analog converter, coupled to the digital interface, for converting digital signals received from the digital interface into analog signals;
a transmit filter, for filtering the analog signals into a first transmit frequency band;
a receive equalizer for amplifying the received analog signals according to a frequency response, comprising:
a first stage, comprising:
a first operational amplifier, having an input and an output;
a first input impedance network, for applying received analog signals, in a first receive frequency band, to the input of the first operational amplifier, and having an impedance selected from one of a first plurality of input impedance values;
and
a first feedback impedance network, coupled between the output and the input of the first operational amplifier, and having an impedance selected from one of a first plurality of feedback impedance values;
and
a second stage, comprising:
a second operational amplifier, having an input, and an output;
a second input impedance network, coupled between the output of the first operational amplifier and the input of the second operational amplifier;
and
a second feedback impedance network, coupled between the output and the input of the second operational amplifier;
an analog-to-digital converter, coupled to the receive analog filter, for converting the filtered analog signals into digital signals;
and
a receive digital filter, coupled to the analog-to-digital converter, for applying a digital filter function to the converted digital signals, and having an output coupled to the digital interface.

20 more elements

Dependencies are inferred from the claim text.

Analog receive equalizer for digital-subscriber-line communications system

Life of this patent

Analog receive equalizer for digital-subscriber-line communications system

Life of this patent

Abstract

Claims27