Telephonic communications – Call signal generating
Reexamination Certificate
2000-04-12
2004-11-02
Barnie, Rexford (Department: 2643)
Telephonic communications
Call signal generating
C379S413010, C379S350000
Reexamination Certificate
active
06813353
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to ringing voltage generators for telephone networks, and is particularly directed to a new and improved ringing voltage supply scheme that involves the subdivision of a ringing bus into multiple ringing bus segments, to which redundant or auxiliary ringing voltage generators are selectively connectable, so as to ensure delivery of a ringing voltage signal as needed, regardless of a failure of a ringing voltage generator and/or removal of a ringing voltage generator card from its associated channel bank.
BACKGROUND OF THE INVENTION
Digital subscriber loop (DSL) channel banks often require the generation of an AC voltage as a ringing signal on a customer's POTS (plain old telephone service) line. This ringing signal is customarily generated as a periodic AC voltage waveform (e.g., sinusoidal, trapezoidal, etc.), having a relatively low frequency (for example, 16.5 Hz, 20 Hz, 25 Hz, 50 Hz are typical ringing frequencies). As a non-limiting example, the ringing voltage may comprise a sinusoidal waveform having an amplitude in a range on the order of from 40 to 120 Vrms riding on a DC voltage in a range on the order of from −30 to −70 VDC. In order to reduce amplitude variations for varying line/load conditions, it is generally desirable to employ closed loop regulation of the ringing voltage. In addition, it is also desirable to provide ringing voltage generation redundancy, in order to keep the telephone circuit operative in the event of a failure of a ringing generator module/card. Due to the statistical nature of the demand for ringing signal generation, it is further advantageous to have the full output power capability of any given ringing voltage generator available to meet peak demands.
Closed loop regulation of a sinusoidal (ringing) voltage that is available from multiple parallel-connected sources can involve the sharing of output voltage, feedback signals, reference voltages, and a reference (pulse width modulated (PWM)) clock. For true redundant or back-up operation, it is necessary to be able to isolate any ringing voltage generator in the event of a failure, since the failure of a generator connected directly in parallel with one or more other generators will disable every other unit until the failed generator can be identified and isolated or removed from the system. This can be a particularly cumbersome task, since identification of the faulty unit typically involves isolating and testing each generator on a one-by-one basis.
SUMMARY OF THE INVENTION
In accordance with the present invention, the desire to provide redundant telephone ringing voltage generator capability, without the shortcomings described above, is successfully addressed by subdividing the ringing voltage bus into multiple bus segments, and providing a plurality of redundant or auxiliary ringing voltage generators, that are individually and selectively connectable to multiple ringing bus segments. In the event of a failure of a ringing voltage generator, that faulty generator is automatically disconnected from its associated ringing bus segment, and that ringing bus segment is connected to a redundant ringing voltage generator.
In a first embodiment, a controlled ringing voltage source of each ringing generator is coupled to a failure detector and relay control circuit and to a relay circuit, which is configured to normally interconnect first and second ringing bus segments, and to isolate the ringing voltage generator from the ringing bus in the event of a failure. Only when energized does the relay couple the ringing voltage produced by the ringing voltage generator to its associated bus segment. Thus, if the relay control circuit detects an acceptable ringing voltage waveform from the ringing voltage generator, it energizes the relay, to isolate the two bus segments and couple the ringing voltage to its associated bus segment. However, if the failure detector and relay control circuit detects a faulty ringing voltage waveform from the ringing voltage generator, it maintains the state of its relay, so that the faulty ringing voltage is isolated, and both ringing bus segments are shorted together, to be supplied with a ringing voltage from the other ‘redundant’ ringing generator. Thus, as long as both ringing voltage generators are operating within normal parameters, each will supply a ringing voltage to its associated bus segment. However, during a failure, each voltage generator unit de-energizes its relay, so that its bus segment may be driven by the ringing generator associated with the other bus segment.
Although the first embodiment provides ringing voltage generation and fault isolation, it will not maintain the bus segments connected if either ringing generator module/card is physically removed from its channel bank card slot. To obviate this potential problem, switching path connections to the bus segments may be modified to include additional cross-coupled bus-shorting switching devices that are respectively controlled by the other ringing generator module. As in the first embodiment, if the failure detector and relay control circuit determines that the ringing voltage waveform is defective, it keeps its ringing voltage coupling relay de-energized, so that the defective ringing voltage generator is isolated from the ringing bus. In addition, it allows the bus-shorting relay on the other module to maintain the two bus segments coupled together, so that they may both receive ringing voltage from the other redundant generator.
In accordance with a third embodiment of the invention, auxiliary signals associated with the ringing voltage, such as zero-crossing signals, status signals, synchronization signals and the like, have their signaling paths segmented in association with the segmentation of the ringing voltage leads. For the case of zero-crossing signals, as a non-limiting example, zero-crossing detectors are provided to minimize noise transients and stress on downstream ringing voltage switching devices connected to the ringing bus segments. Each relay is configured as a double-pole relay to couple an additional zero-crossing detection signal to an associated zero-crossing line; the relay control circuit has a zero-crossing detection output that changes state at the time of occurrence of a zero-crossing in the monitored ringing voltage waveform.
As in the second embodiment, if the failure detector and relay control circuit determines that the monitored parameters of the ringing voltage waveform are acceptable, it operates an associated relay to couple the ringing generator to its associated bus segment, and to couple the zero-crossing output to the zero-crossing line associated with the ringing voltage generated by the ringing generator. However, for a faulty ringing voltage waveform, it will maintain the relay de-energized, so that the ringing bus segment is isolated from the ringing voltage generator and the zero-crossing output is isolated from the zero-crossing line.
In addition to the first double-pole relay, a respective ringing generator module of the third embodiment includes a second double-pole, bus-shorting relay coupled to the segmented ringing bus, and the segmented zero-crossing bus. This bus-shorting relay is controlled by an inverted output of the failure detector and relay control circuit of the other ringing generator module. This ‘inverter-coupled’ circuit configuration performs the same relay control functionality as the second embodiment; however, it operates only one relay at any time, and thereby reduces the amount of drive current required by the control signal and reduces power wasted in the relay during normal operation. The use of an inverter ensures that the contacts of each relay will be open at the time of insertion of the circuit card containing those relays into a channel bank, which eliminates surge currents and noise transients during card insertion.
The ringing voltage and zero-crossing redundancy functionality of the present invention may be extended to any number of ri
Boudreaux, Jr. Ralph R.
McGary John S.
Robinson Steven M.
Adtran Inc.
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Barnie Rexford
LandOfFree
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