Ring trip circuit for subscriber telephone

Details Ring trip circuit for subscriber telephone Ring trip circuit for subscriber telephone

1989-02-21

1991-02-19

Dwyer, James L.

Telephonic communications

Supervisory or control line signaling

Using line or loop condition detection

379405, 379373, 379251, H04M 302

Patent

active

049951114

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

a. Field of the Invention
The present invention relates to a ring trip circuit for a subscriber telephone, by which an on-hook state or an off-hook state of the telephone is detected. More particularly, it relates to an improved ring trip circuit which has a reduced size and can be formed by a large scale integrated circuit.
b. Description of the Related Art
Ring trip circuits are provided in a telephone exchanger (or switching board) for detecting an on-hook state or off-hook state of subscriber telephones. Each ring trip circuit is connected to a subscriber line, i.e., a ring trip circuit must be provided for each subscriber telephone. Since the telephone exchanger processes a large number of subscriber lines, for example, over 20,000 subscriber lines, a large number of ring trip circuits are provided in the telephone exchanger.
The ring trip circuit of the prior art are bulky and are not suitable to be formed by a large scale integrated circuit (LSI). Also, the ring trip circuits of the prior art are expensive.
The prior art ring trip circuit will be described in more detail later with reference to the drawings.


SUMMARY OF THE INVENTION

An object of the present invention is to provide a ring trip circuit which can be formed in a small size and by a large scale integrated circuit.
Another object of the present invention is to provide a ring trip circuit which can be manufactured at a low cost.
According to a basic aspect of the present invention, there is provided a ring trip circuit for a subscriber telephone, including: a voltage detecting circuit, operatively connected between both ends of a ringer sending resistor operatively connected between the subscriber telephone and a ringer source, for detecting a voltage difference between both ends of the ringer sending resistor, and having a circuit converting the voltage difference to a current difference the voltage difference varying in response to whether the subscriber telephone, in an on-hook state or an off-hook state; and a state detecting circuit, operatively connected to the voltage detecting circuit, for detecting the on-hook state or the off-hook state of the subscriber telephone in response to a value corresponding to the voltage difference. The voltage detecting circuit is formed by a plurality of current mirror circuits, each of which includes at least two transistors, and the state detecting circuit includes a comparator circuit formed by a plurality of transistors, so that the ring trip circuit is formed in a small size and is adaptive to be formed by a large scale integrated circuit.
According to one aspect of the present invention, the voltage detecting circuit includes a first current switching circuit operatively connected to one end of the ringer sending resistor, and having first to third ports, the first current switching circuit flowing a first current from the second port to the third port when a voltage at one end of the ringer sending resistor is positive, or flowing the first current from the first port to one end of the ringer sending resistor through the third port when the voltage at one end of the ringer sending resistor is negative, a second current switching circuit operatively connected to another end of the ringer sending resistor, and having first to third ports, the second current switching circuit flowing a second current from the second port to the third port when another voltage at another end of the ringer sending resistor is positive, or flowing the second current from first port and flowing the same to another end of the ringer sending resistor through the third port when the another voltage at another end of the ringer sending resistor is negative, a first current mirror circuit having a first terminal connected to the first port of the first current switching circuit and a second terminal, a second current mirror circuit having a first terminal connected to the second port of the first current switching circuit and a second terminal connected to the second terminal of the first c

REFERENCES:
patent: 3941939 (1976-03-01), Holmes et al.
patent: 4356355 (1982-10-01), Ferrieu et al.
patent: 4447675 (1984-05-01), Arntsen et al.
patent: 4827505 (1989-05-01), Takato et al.

Affiliated with

Also associated with

Rating

Ring trip circuit for subscriber telephone does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Ring trip circuit for subscriber telephone, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ring trip circuit for subscriber telephone will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-1150828