At&t Bell Laboratories

Bell Telephone Laboratories

Rouben Toumani

Tom D Arntsen

Milton L Embree

Joseph H Havens

An origination scan circuit for detecting circuit closure state in a loop circuit has a much lower impedance than does the typical loop circuit. Its source impedance is split into separate resistive parts for connecting opposite terminals of an office battery to the tip and ring leads of the loop. Currents in the separate resistive parts are sensed and summed for comparison against a threshold current to indicate whether or not a subscriber station on the loop is off hook. Threshold current magnitude is variable to accommodate loop start and ground start applications. When the off-hook state is detected, the origination scan circuit is disabled by switching open the resistive part connections, and loop current is thereafter provided by other suitable means. Automatic current limiting arrangements are included for converting the switching functions to high impedance circuit elements.

Low resistance origination scan circuit

Resistive circuits are provided at the input of an electronic battery feed circuit feedback path for lowering the voltage level of feedback signals to a metallic signal feedback portion and a common mode signal feedback portion so a common mode amplifier can be implemented in a much lower voltage technology than line amplifiers of the battery feed circuit. Additional resistive circuits at the feedback output apply metallic signals to complementary inputs of the tip and ring line amplifiers without requiring a phase splitting amplifier. In addition, signals derived from the feedback circuit are used to vary the supply voltage for the line feed circuit elements as a function of feedback signal level and to provide a common mode reference signal which causes the tip and ring amplifiers to be biased symmetrically with respect to ground and the variable negative supply.

Electronic battery feed circuit for telephone systems

A ring-trip detector circuit is disclosed which detects a subscriber off-hook condition in the presence of a ringing signal. The ring-trip detector employs substantially all low-voltage components which enables it to be fabricated using integrated circuit techniques with the resultant cost and space-saving advantages inherent therein. The ringing signal is disabled upon detection of a DC component which is present in the telephone loop only when the subscriber goes off-hook. This circuit detects the DC voltage component across a resistor (20) in series with the ringing source (19) and the telephone loop (12, 13). The voltage across this resistor (20) is converted by resistance networks (23, 24) into two relatively small currents that are fed to low impedance points (25, 26). A difference current is formed therebetween, which is filtered (31, 45) to remove AC components, and compared with a threshold current (29, 46). Ring-trip occurs when the filtered difference current exceeds the threshold.

Ring-trip detector

A buck boost type noninverting transformerless switching regulator utilizes two synchronized switches operating at either the same or different duty cycles to independently control energy storage and energy delivery from a two terminal inductor element to the output load. A wide range of output voltage is available and is continuously regulated.

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Randolph, NJ, United States of America

Rouben Toumani