Abstract: A signal limiting amplifier includes interstage limiting devices to restrict the range of output voltage signals. The devices are base-emitter circuits of transistors, one of which operates in response to one polarity of signals and has its collector terminal unconnected, and the other of which operates in response to the other polarity of signals and has its collector circuit connected (when limiting) to operate an appropriate utilization circuit. In one embodiment, the limiting amplifier is applied as a common mode feedback amplifier in a telephone line feed circuit, and the limiter signal is used to limit large longitudinal signals on a customer line and to power down the line feed circuit in the event the limited signals persist beyond a certain interval.

Abstract: A single chip, bipolar logic circuit receives input signals in a differential amplifier or comparator stage coupled, without saturation, by differential current mirrors to drive an output stage of the push-pull variety. Various circuit arrangement are included to keep other bipolar transistors out of their saturation operating regions, and master transistors of the current mirror are provided with trickle bias when in the operating state to hold them at turn-on threshold for fast response to changes in state of the digital signals.

Abstract: A ringing signal generator is disclosed for remotely generating telephone ringing signals having a trapezoidal waveform. A single capacitor and two constant current sources control the wave shape while current limiting is provided on both the positive going and negative going half-cycles of the ringing signal. A voltage offset is provided between the ringing signal source and the subscriber line to prevent loading the ringing signal with the subscriber line feed circuit.

Abstract: A relay driver circuit is disclosed in which a relay coil is operated by enabling the collector-emitter path of a switching transistor. In order to avoid damage to the transistor from voltages induced in the relay coil when the relay is turned off, an isolating semiconductor device is inserted between the transistor and the relay coil. This semiconductor device is operated in synchronism with the driving transistor and thus isolates the driving transistor from transients during the de-energization of the relay.

Abstract: A subscriber loop carrier system is disclosed in which a plurality of telephone subscriber communications channels are frequency-multiplexed on a single wire pair using analog modulation techniques. Supervisory signaling for each channel is accomplished by modulating the channel carrier with a plurality of tones coded so as to represent a plurality of supervisory functions including multiparty superimposed ringing (four-party fully selective, eight-party semiselective), two-party ringing and tip party identification, and standard single party ringing, as well as off-hook and dial pulse superivision. The system is designed to be universally compatible with any of the above classes of service.