The present invention is an improved subscriber line interface circuit which allows fast detection of an off-hook signal in the presence of a ringing signal during an answer mode while also permitting fast detection of dialing pulses during a calling mode. A programmable filter is used in the supervision circuit of the SLIC to allow the cutoff frequency of the filter to be varied so that the 20 Hz ringing signal will be attenuated during a ringing sequence and dialing pulse rates up to 20 Hz will be passed by the filter during the calling mode. A clamping amplifier is used to clamp the received signal to a maximum of 1.5 times the loop threshold current. This eliminates the large variations in the rise and fall times of the pulse dialing signal due to variations in the loop current caused by varying impedances of the telephone line. The filter is programmed by using an analog switch to bypass certain filter elements. The analog switch is a voltage-follower amplifier which has a current source which is disabled when the switch is to be opened.

Monolithic telephone subscriber line interface circuit

An internal power-source potential supply circuit for supplying an internal power-source potential with high accuracy is disclosed. An external power-source potential (VCE) is connected to the source of a PMOS transistor (Q 1 ) having a drain for applying an internal power-source potential (VCI) to a load ( 11 ) and a gate receiving a control signal (S 1 ) from a comparator ( 1 ). The comparator ( 1 ) outputs the control signal (S 1 ) on the basis of a comparison result between a reference potential (Vref) and a divided internal power-source potential (DCI). The drain of the PMOS transistor (Q 1 ) is connected to a first end of a resistor (R 1 ), and a current source ( 2 ) is connected between a second end of the resistor (R 1 ) and ground. A voltage provided at a node (N 1 ) serving as the second end of the resistor (R 1 ) is applied to a positive input of the comparator ( 1 ) as the divided internal power-source potential (DCI).

Internal power-source potential supply circuit, step-up potential generating system, output potential supply circuit, and semiconductor memory

In accordance with an embodiment, a method includes conducting a reverse current through a first switch that includes a normally-on transistor coupled in series with a normally-off transistor between a first switch node and a second switch node. While conducting the reverse current, the first switch is turned-off by turning-off the normally-off transistor via a control node of the normally-off transistor and reducing a drive voltage of the normally-on transistor by decreasing a voltage between the control node of the normally-on transistor and a reference node of the normally-on transistor. After turning-off the first switch, a second switch coupled to the first switch is turned on.

System and method for a switch having a normally-on transistor and a normally-off transistor

A change-over circuit for use in a tester for changing over a load and a driver to be connected to a device under test is implemented by using diode-bridge type analog switches which include a first diode-bridge type analog switch connected as collector loads for first and second transistors, a second diode-bridge type analog switch connected as collector loads for third and fourth transistors, respectively. The driver is connected to an input of the first diode-bridge type analog switch. The load circuit is connected to an input of the second diode-bridge type analog switch. The first and second diode-bridge type analog switches are so interconnected as to perform a differential operation in response to an ON/OFF control signal applied to the fourth transistor from the first transistor for thereby changing over the current and capacitive loads and the driver to be coupled to the device under test which is connected to outputs of the first and second diode-bridge type analog switches. The current and capacitive loads can both be turned on and off through differential cooperation of the first and second diode-bridge type analog switches to thereby allow the current and capacitive loads to be connected simultaneously or separately only when the driver is disabled or inhibited. Inexpensive and simplified switch circuit is thus provided.

Change-over circuit for tester implemented by using diode-bridge type analog switches

An information separation device that having a transformer operating as a separating filter to separate alternating voltage information and transmitted direct current power. The transformer has at least one winding on a first side coupled to the do power. A capacitor is coupled to this winding, at whose ends direct current power is made available. The transformer has one winding on an information processing side. First and second valves are arranged in a transmitting branch parallel to the capacitor, the second winding being coupled at its first end between the first and second valves. Third and fourth valves are arranged in a branch parallel to the capacitor, the second winding being coupled in series at its first and second ends between the third and fourth valves in phase opposition to the first and second valves.

Information separation device

A line circuit for connecting a subscriber line to a telephony system that avoids the use of electro-mechanical elements such as relays. A bridge circuit includes a bilateral current gate in each of the tip and ring lines that can couple or inhibit signals from passing between the subscribed lines and the system. When the bilateral current gates are in an inhibit mode, an on-hook current source energizes the tip and ring lines. A detector senses when the subscriber goes off-hook, and also the dial pulses. After the current gate goes into a coupling mode, the on-hook current source and detector are electrically inactive, and an off-hook current source thereafter provides current to the tip and ring conductors.

All electronic interface for telephony system

A bilateral, low loss, wide band, concentrator circuit selectively controls the transfer of a signal between one of a plurality of first terminals and a single, second terminal. The balance points of each of a plurality of bilateral current gates connect to one of the first terminals and to the second terminal. A floating power supply and selection switches selectively forward bias one of the bilateral current gates so it operates as a modulator in which the signal to be switched is modulated onto the bias current thereby to form a low-loss, wide-band path between the selected first terminal and the second terminal.

Concentrator circuit incorporating solid state bilateral bridge arrangement

A bilateral, low loss, wide band, switching circuit controls the transfer of a signal between two terminals. The balance points of a bilateral current gate connect to the terminals. A rectifier forward-biases the bilateral current gate when a controllable switching element forms a return path from the bilateral current gate to the rectifier. When the rectifier is energized, control circuitry closes the conductive path through the switching element to forward-bias diodes in the bilateral current gate so it operates as a modulator in which the signal to be switched is modulated onto the bias current from the rectifier.

Barrie Brightman

Papers

All electronic interface for telephony system

Concentrator circuit incorporating solid state bilateral bridge arrangement

Bilateral electronic switch