Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Amplitude control
Reexamination Certificate
1999-11-10
2001-03-20
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Amplitude control
C327S074000, C330S257000
Reexamination Certificate
active
06204716
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to transient signal detectors, and in particular, to transient signal detectors for detecting transient signal excursions which exceed threshold levels in both positive and negative directions.
2. Description of the Related Art
Many circuit applications can benefit from, or in many cases absolutely require, some form of transient signal detection whereby signals within the monitored signal path which exceed some predetermined threshold and which are frequently transient in nature can be reliably detected. This will allow appropriate responsive action to be initiated, such as filtering or suppression of such transient signals.
One such circuit application is that of a subscriber line interface circuit (SLIC) for telecommunications. Signal transients in a telecommunication environment are quite common. For example, aside from any transient signals introduced by the operating environment (e.g., electrical motors, lightning strikes, ground loops, etc.), transients due to transitions between on-hook and off-hook conditions and normal dialing impulses caused by rotary telephones are often encountered. For many applications, such transients can be problematic and result in unreliable or otherwise unacceptable circuit performance.
Monitoring transient signals in a SLIC application, while already difficult, can be further complicated by the fact that the signal environment is differential in nature due to the “tip” and “ring” signal connections. Accordingly, transient signals with both positive and negative differential signal polarities can be and often are encountered. Accordingly, it would be desirable to have a simple transient signal detection circuit which can detect both positive and negative signal transients in a differential signal environment.
SUMMARY OF THE INVENTION
A transient signal detector in accordance with the present invention provides for the monitoring of a signal line and the generating of a control signal which indicates when the magnitude of the differential signal on the line exceeds either a positive or negative threshold value. Such threshold value can be defined by a single circuit parameter, such as a current, thereby allowing for a single, simple adjustment of the threshold for both the positive and negative threshold values.
In accordance with one embodiment of the present invention, a transient signal detector for monitoring a signal and indicating when such signal has a magnitude which extends in either direction outside of a range defined by positive and negative threshold values includes a differential buffer circuit, an output circuit and a current sinking circuit. The differential buffer circuit is configured to receive a differential signal and in accordance therewith selectively provide first and second currents. The first current is provided when the differential signal has a first polarity and a magnitude which exceeds a first threshold value. The second current is provided when the differential signal has a second polarity and a magnitude which exceeds a second threshold value. The output circuit is configured to selectively convey a third current. The current sinking circuit is coupled to the differential buffer circuit and the output circuit and is configured to: sink the first current when the differential signal has the first polarity and the differential signal magnitude exceeds the first threshold value; sink the second current when the differential signal has the second polarity and the differential signal magnitude exceeds the second threshold value; sink the third current when the differential signal has the first polarity and the differential signal magnitude is less than the first threshold value; and sink the third current when the differential signal has the second polarity and the differential signal magnitude is less than the second threshold value.
In accordance with another embodiment of the present invention, a method of monitoring a signal and indicating when such signal has a magnitude which extends in either direction outside of a range defined by positive and negative threshold values includes the steps of:
receiving a differential signal and in accordance therewith
generating a first internal current when the differential signal has a first polarity and a magnitude which exceeds a first threshold value, and
generating a second internal current when the differential signal has a second polarity and a magnitude which exceeds a second threshold value;
sinking the first internal current when the differential signal has the first polarity and the differential signal magnitude exceeds the first threshold value;
sinking the second internal current when the differential signal has the second polarity and the differential signal magnitude exceeds the second threshold value;
sinking an external current when the differential signal has the first polarity and the differential signal magnitude is less than the first threshold value; and
sinking the external current when the differential signal has the second polarity and the differential signal magnitude is less than the second threshold value.
These and other features and advantages of the present invention will be understood upon consideration of the following detailed description of the invention and the accompanying drawings.
REFERENCES:
patent: 5376898 (1994-12-01), Tanaka et al.
patent: 5736866 (1998-04-01), Harr
Baker & McKenzie
Callahan Timothy P.
National Semiconductor Corporation
Nguyen Minh
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