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US 2003/0169872 A1Published application
Voltage reference filter for subscriber line interface circuit
AssigneeIntersil Americas Inc.
InventorsLeonel E. Enriquez, Douglas L. Youngblood
Life of this patent
Estimating the term…
Abstract
A voltage reference filter for a subscriber line interface circuit removes unwanted noise on a DC reference voltage sourced by a device, such as a codec, and employed by the subscriber line circuit as a differential mode voltage baseline. The DC reference voltage is coupled via a high pass filter to the sense amplifier. The filter blocks the DC component of the reference voltage and passes noise components to the sense amplifier. The reference port of an amplifier between the sense amplifier and a codec receives the same (noisy) reference voltage AC-coupled to the sense amplifier, and performs common mode rejection of noise components riding on the DC reference.
Claims18
An apparatus comprising:
- an input port to which an input signal is applied;
- an output port from which an output signal is derived;
- a signal processing circuit coupled between said input and output ports, and being operative to process said input signal applied to said input port and to generate said output signal, in accordance with a prescribed relationship between said input signal and a DC reference applied to a reference port of said signal processing circuit, said DC reference being subject to the presence of unwanted noise components;
- and
- an AC filter having an input coupled to receive said DC reference, and an output coupled to a signal transport path through which said input signal is coupled to said input port, said AC filter having a transfer function that is operative to pass said noise components that may be present on said DC reference to said input port, but to block the DC component of said DC reference from application to said input port;
- said signal processing circuit performing common mode rejection of said noise components that may be present on said DC reference, so that said output signal at said output port has substantially reduced noise components which, when coupled to downstream differential mode processing circuitry that is coupled to said DC reference, are effectively canceled.
3 more elements
A subscriber line interface circuit comprising:
- an input signal receiving unit, that is operative to interface input signals, supplied from a digitally programmable signal generation and processing unit;
- a multi-mode tip/ring amplifier unit, having tip and ring outputs adapted to be coupled to tip and ring conductors of a subscriber loop pair, and inputs coupled to receive and amplify said input signals, in accordance with the mode of operation of said subscriber line interface circuit;
- a sense amplifier coupled to outputs of said tip and ring amplifier sections of said dual mode tip/ring amplifier and being operative to provide a voice signal summation for differential mode voice signals, and mutual cancellation of common mode signals;
- an operational amplifier having a first input coupled to receive a DC reference from an external device to which said subscriber line interface circuit is coupled, and a second, opposite polarity, input coupled to receive the output of said sense amplifier, said operational amplifier having an output coupled as an input to said external device;
- and
- an AC filter having an input coupled to receive said DC reference, and an output coupled to an input of said sense amplifier, said AC filter having a transfer function that is operative to pass noise components that may be present on said DC reference, but to block the DC component of said DC reference from application to said sense amplifier;
- said operational amplifier circuit performing common mode rejection of said noise components that may be present on said DC reference, so that the output of said operational amplifier has substantially reduced noise components which, when coupled to downstream differential mode processing circuitry that is coupled to said DC reference, are effectively canceled.
4 more elements
A method for interfacing communication signals with a wireline pair comprising the steps of:
- (a) providing a subscriber line interface circuit having an input signal receiving unit, that is operative to interface input signals with a tip/ring amplifier unit, having tip and ring outputs thereof coupled to tip and ring conductors of said wireline pair, and inputs coupled to receive and amplify said input signals, a sense amplifier coupled to outputs of said tip and ring amplifier sections of said dual mode tip/ring amplifier and being operative to provide a voice signal summation for differential mode voice signals, and mutual cancellation of common mode signals, and an operational amplifier having a first input coupled to receive a DC reference from an external device to which said subscriber line interface circuit is coupled, and a second, opposite polarity, input coupled to receive the output of said sense amplifier, said operational amplifier having an output coupled as an input to said external device;
- and
- (b) coupling an input of an AC filter to said DC reference, and an output to an input of said sense amplifier, said AC filter having a transfer function that is operative to pass to said tip/ring signals and noise components that may be present on said DC reference, but to block said DC reference from application to said sense amplifier, whereby said operational amplifier performs common mode rejection of said noise components that may be present on said DC reference, so that the output of said operational amplifier has substantially reduced noise components which, when coupled to downstream differential mode processing circuitry that is coupled to said DC reference, are effectively canceled.
Dependencies are inferred from the claim text.