Telephone line interface with AC and DC transconductance loops

• US 5,500,894 A
• Filed: 12/03/1993
• Issued: 03/19/1996
• Est. Priority Date: 12/03/1993
• Status: Expired due to Term

• Current Assignee: Maxim Integrated Products, Inc. (Analog Devices, Inc.)
• Original Assignee: Silicon Systems, Inc. (Texas Instruments, Inc.)
• Inventors: Hershbarger, Russell A.
• Primary Examiner(s): Hofsass, Jeffery
• Assistant Examiner(s): Wolinsky, Scott
• Application Number:
  US08/161,740
• Time in Patent Office: 837 Days
• Field of Search: 379/399, 379/414, 379/415, 379/413, 379/405, 379/324
• US Class Current: 379/399.02
• CPC Class Codes: H04M 3/005 Interface circuits for subscriber lines current supply H04M19/00 and subgroups; supervisory, monitoring or testing arrangements H04M3/22 and subgroups; in key telephone systems H04M9/006

Abstract

A method and apparatus for providing a telephone line interface having selectable termination characteristics, such as impedance parameters, is provided using AC and DC transconductance loops. The present invention may be used with modem apparatus to provide regulatory compliance of line termination characteristics in multiple countries having different, even conflicting, standards or regulations. The preferred embodiment of the present invention uses a programmable switched capacitor filter to drive a transconductance driver that drives the telephone line. An AC transconductance loop controls AC transconductance characteristics, while a DC transconductance loop controls DC transconductance characteristics.

Claims

1. A method for controlling the characteristics of a telephone line interface circuit comprising the steps of:

using a DC transconductance loop to control DC characteristics of a telephone apparatus;

using an AC transconductance loop to control AC characteristics of said telephone apparatus, said AC transconductance loop deriving a power supply voltage from a telephone line, wherein Said step of using an AC transconductance loop to control said AC characteristics of said telephone apparatus comprises the steps of;

AC coupling a telephone line input to a first switched capacitor filter;

coupling a first filter output of said first switched capacitor filter to a first input of a first transconductance driver;

coupling a first telephone line output from said first transconductance driver to a telephone line;

and wherein said step of using a DC transconductance loop to control said DC characteristics of said telephone apparatus comprises the steps of;

DC coupling a telephone line input to a programmable continuous time filter;

coupling a second filter output from said programmable continuous time filter to a second input of a second transconductance driver;

coupling a second telephone line output from said second transconductance driver to said telephone line.

2. A telephone line interface comprising:

an AC transconductance loop for controlling AC characteristics, said AC transconductance loop deriving a power supply voltage from a telephone line, wherein said AC transconductance loop comprises;

an AC coupling component;

a first switched capacitor filter for receiving a telephone line input signal and for providing a first filter output signal;

a transconductance driver for receiving said first filter output signal and for providing a first telephone line output signal;

said telephone line interface further comprising;

a DC transconductance loop for controlling DC characteristics, wherein said DC transconductance loop comprises;

a programmable continuous time filter for receiving a telephone line input signal and for providing a second filter output signal;

a transconductance driver for receiving said second filter output signal and for providing a second telephone line output signal.

3. The telephone line interface of claim 2 wherein said AC coupling component comprises a capacitor.