Dynamically adjustable digital gyrator having extendable feedback for stable DC load line
First Claim
1. A digital gyrator, comprising:
- a digital filter to emulate an inductance on a telephone line serviced by said digital filter, said digital filter being initially settable to a first cutoff frequency; and
an oscillation checker module to detect an amplitude of oscillation on said telephone line serviced by said digital filter, said oscillation checker module adapted to reset said digital filter to a second cutoff frequency lower than said first cutoff frequency as a function of said detected oscillation level;
wherein said gyrator resets said digital filter to a third cutoff frequency after a predetermined period of time after said digital gyrator causes telephone equipment to enter an off-hook condition.
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Accused Products
Abstract
A dynamically adjustable digital gyrator device for a telephone line interface (e.g., a DAA) utilizing extended feedback and a dynamically adjustable filter to achieve stable convergence in the control of DC line current on a telephone line a short period of time. The low pass filter of the digital gyrator includes at least two (2) different fast filter settings and at least two (2) different slow filter settings based on possible load terminations (e.g., PBX, TAS, etc.), which can be determined based on the dynamic detection of an oscillation on the line. For instance, in a disclosed example, a voice band modem system is allowed to go off-hook with a 1 Hz cutoff low pass filter, and then the output of the low pass filter is checked for an oscillation. If an oscillation is detected, then the poles and/or zeroes of the low pass filter cutoff are changed to a slower convergence rate cutoff frequency (e.g., to 0.1 Hz). As a result, the exemplary voice band modem will converge stably and quickly (e.g., in less than 1 second) before dialing begins. By controlling the DC line current digitally, software can be used to set the DC line current in accordance with predefined characteristics. Predefined characteristics can be set to accommodate varying country specifications instead of using switches to control resistors and capacitors.
30 Citations
22 Claims
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1. A digital gyrator, comprising:
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a digital filter to emulate an inductance on a telephone line serviced by said digital filter, said digital filter being initially settable to a first cutoff frequency; and
an oscillation checker module to detect an amplitude of oscillation on said telephone line serviced by said digital filter, said oscillation checker module adapted to reset said digital filter to a second cutoff frequency lower than said first cutoff frequency as a function of said detected oscillation level;
wherein said gyrator resets said digital filter to a third cutoff frequency after a predetermined period of time after said digital gyrator causes telephone equipment to enter an off-hook condition. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method of regulating a signal on a telephone line, comprising:
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digitizing a signal received from said telephone line;
filtering said digitized signal with a digital low pass filter having a first cutoff frequency;
detecting an amplitude of oscillation in said signal at said telephone line;
adjusting said digital low pass filter to have a second cutoff frequency lower than said first cutoff frequency to dampen said detected oscillation if an amplitude of said oscillation indicates an unstable pre-charge state of said telephone; and
after a pre-charge period of said telephone line, adjusting said digital low pass filter to have a third cutoff frequency relating to a steady state of said telephone line. - View Dependent Claims (10, 11, 12)
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13. Apparatus for regulating a signal on a telephone line, comprising:
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means for digitizing a signal received from said telephone line;
means for filtering said digitized signal with a digital low pass filter having a first cutoff frequency;
means for detecting an amplitude of oscillation in said signal on said telephone line;
means for adjusting said digital low pass filter to have a second cutoff frequency lower than said first cutoff frequency to dampen said detected oscillation if an amplitude of said oscillation indicates an unstable pre-charge state of said telephone; and
means for adjusting said digital low pass filter after a pre-charge period of said telephone line, to have a third cutoff frequency relating to a steady state of said telephone line. - View Dependent Claims (14, 15, 16)
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17. An integrated circuit including a digital gyrator, comprising:
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a digital filter to service a telephone line, said digital filter being initially settable to a first cutoff frequency; and
an oscillation checker module to detect a presence of undesirable oscillation on said telephone line serviced by said digital filter, said oscillation checker module adapted to reset said digital filter to a second cutoff frequency lower than said first cutoff frequency if said undesirable oscillation is present;
wherein said digital gyrator resets said digital filter to a third cutoff frequency associated with a steady state of said telephone line after a predetermined period of time after said digital gyrator causes telephone equipment to enter an off-hook condition. - View Dependent Claims (18, 19, 20, 21, 22)
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Specification