Subscriber line interface circuit for controlling AC and DC output impedance
First Claim
1. A subscriber line interface circuit (SLIC) having first and second inputs, comprising:
- first means coupled to the first and second inputs of the SLIC for receiving first and second transmission signals having AC and DC signal levels, said first means sensing AC common mode variation and AC differential variation of said first and second transmission signals for providing a common mode feedback signal and a differential feedback signal, said first means including,(a) a first amplifier having first and second inputs and an output, said output being coupled to said first input of said first amplifier, said first amplifier receiving first and second power supply potentials less than said DC signal level on said first transmission signal,(b) a second amplifier having first and second inputs and an output, said output being coupled to said first input of said second amplifier, said second amplifier receiving said first and second power supply potentials less than said DC signal level on said second transmission signal,(c) a first resistor and a first capacitor serially coupled between the first input of the SLIC and said second input of said first amplifier,(d) a second resistor and a second capacitor serially coupled between the first input of the SLIC and said second input of said first amplifier,(e) a third resistor coupled between said output of said first amplifier and a first node, and(f) a fourth resistor coupled between said output of said second amplifier and said first node for providing said common mode feedback signal; and
second means coupled to the first and second inputs of the SLIC for providing an AC output impedance, said second means receiving said common mode feedback signal and said differential feedback signal for controlling said AC output impedance.
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Accused Products
Abstract
A subscriber line interface circuit (SLIC) sets AC and DC output impedances as seen by first and second transmission signals. The common mode variation and differential variation of the first and second transmission signals is AC-sensed to provide a common mode feedback signal and a differential feedback signal which in turn controls the AC output impedance. The DC component of the first and second transmission signals is blocked allowing downstream amplifiers to operate at reduced power supply potentials. The DC variation of the first and second transmission signals is also sensed for providing a DC feedback signal to control the DC output impedance.
93 Citations
10 Claims
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1. A subscriber line interface circuit (SLIC) having first and second inputs, comprising:
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first means coupled to the first and second inputs of the SLIC for receiving first and second transmission signals having AC and DC signal levels, said first means sensing AC common mode variation and AC differential variation of said first and second transmission signals for providing a common mode feedback signal and a differential feedback signal, said first means including, (a) a first amplifier having first and second inputs and an output, said output being coupled to said first input of said first amplifier, said first amplifier receiving first and second power supply potentials less than said DC signal level on said first transmission signal, (b) a second amplifier having first and second inputs and an output, said output being coupled to said first input of said second amplifier, said second amplifier receiving said first and second power supply potentials less than said DC signal level on said second transmission signal, (c) a first resistor and a first capacitor serially coupled between the first input of the SLIC and said second input of said first amplifier, (d) a second resistor and a second capacitor serially coupled between the first input of the SLIC and said second input of said first amplifier, (e) a third resistor coupled between said output of said first amplifier and a first node, and (f) a fourth resistor coupled between said output of said second amplifier and said first node for providing said common mode feedback signal; and second means coupled to the first and second inputs of the SLIC for providing an AC output impedance, said second means receiving said common mode feedback signal and said differential feedback signal for controlling said AC output impedance. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A subscriber line interface circuit (SLIC) having first and second inputs, comprising:
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first means coupled to the first and second inputs of the SLIC for receiving first and second transmission signals having AC and DC signal levels, said first means sensing DC variation of said first and second transmission signals for providing a DC feedback signal, said first means including, (a) a first amplifier having first and second inputs and an output, said first input of said first amplifier receiving a first power supply potential, (b) a first resistor coupled between the first input of the SLIC and a first node, (c) second and third resistors serially coupled between said first node and said second input of said first amplifier, and (d) a fourth resistor coupled between said output of said first amplifier and said second input of said first amplifier; and second means coupled to the first and second inputs of the SLIC for providing a DC output impedance in response to said DC feedback signal, said second means including (e) a second amplifier having first and second inputs and an output, (f) a fifth resistor coupled between said output of said first amplifier and said first input of said second amplifier, (g) a sixth resistor coupled between said first input of said second amplifier and said first node, (h) a seventh resistor coupled between said first node and said output of said second amplifier, and (i) an eighth resistor coupled between said output of said second amplifier and said second input of said second amplifier. - View Dependent Claims (9, 10)
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Specification