Abstract: A programmable signal generator is disclosed which includes a source of a user control signal. A controlled clock signal generator produces one of a predetermined setof respective clock signals responsive to the user control signal. Means are coupled to the clock signal generator for converting the clock signals to an analog sine-wave.

Abstract: A ringing signal generator includes a low power signal generator for generating a relatively low power signal representing a ringing signal, a bipolar pulse generator for generating a series of bipolar pulses having widths representing the amplitude of the low power signal, wherein adjoining pulses have opposite polarities, and a high power ringing signal generator for producing a high power ringing signal in response to the series of bipolar pulses. An analog sine wave signal is superimposed upon a DC bias signal to produce the low power signal.

Abstract: An overload protection circuit for power supplies and telecommunications apparatus such as multifrequency ringing generators causes the output voltage to become zero when a current overload is detected. The voltage is kept at zero for a predetermined period of time. Then the output voltage is restored. If an overload is still detected, the output voltage is again brought to zero.

Abstract: A series ringing signal generator is disclosed which comprises a source of a user control signal. A programmable ringing signal generator is provided for generating an analog sine wave signal having a selectable amplitude and frequency in response to a selection signal. Finally, sequencing means, coupled between the source of the user control signal and the programmable ringing signal generator, is provided for generating a sequence of selection signals in response to said user control signal.

Abstract: A programmable ring signal generator includes a source of a user control signal. A controlled clock signal generator produces one of a set of respective clock signals responsive to the user control signal. A switched capacitor filter is coupled to the clock signal generator for converting the clock signals to an analog sine-wave. Finally, a power amplifier, coupled to the sine-wave converter, produces the ring signal.

Abstract: The present invention provides a power drive circuit which is transformer isolated from the circuit developing the drive signals, but which does not lose its DC reference voltage. This technique results in the desired isolation without the undesirable possibility of operating the output transistors in an unsafe DC region, which is a particular problem when the output transistors are FET devices. In accordance with the present invention, pulse transformers are used to drive the power FET devices.

Abstract: An improved loop current supply circuit including a first amplifier connected to a source of bias voltage. The first amplifier is further connected to a subscriber loop circuit through the tip and ring conductors. The first amplifier receives the bias voltage and supplies loop current to the loop circuit. A second amplifier connected to the tip and ring conductors outputs a voltage representative of the amount of current in the subscriber loop. When the output voltage of the second amplifier becomes greater than the bias voltage, a loop voltage network connected to the second amplifier and to the bias voltage source shunts the bias voltage from the first amplifier, decreasing the current in the loop circuit.

Abstract: An improved AC impedance matching arrangement including a first amplifier connected to a subscriber loop through the tip and ring conductors of a subscriber line circuit. The first amplifier is arranged to supply loop current to the subscriber loop through first and second resistors. Each resistor having a set DC value. A second amplifier connected to the tip and ring conductors is arranged to develop and output a signal responsive to AC signals applied to the tip and ring conductors from the subscriber loop. A feedback circuit connected to the second amplifier is arranged to receive the second amplifier output signal and develop and output to the first amplifier an impedance matching signal. The impedance matching signal raises the impedance seen by the tip and ring conductors above the set DC value of the first and second resistors.

Abstract: An improved offhook supervision circuit including an amplifier connected to a subscriber loop through the tip and ring conductors of a subscriber line circuit. The amplifier is arranged to develop and output a loop voltage signal representing the level of the DC signals applied to the subscriber loop circuit. A comparator device has a first input connected to the amplifier and is arranged to receive the loop voltage signal output by the amplifier. A second input of the comparator device is connected to a reference voltage device which outputs a predetermined reference signal voltage. Any significant reduction of the DC signal level on the loop circuit will cause the loop signal voltage output by the amplifier to fall below the reference signal voltage. An offhook signal is then output from the comparator device to a control device signaling an offhook condition.

Abstract: A circuit which prepares a conductive path between a ringing voltage generator and a telephone subscriber loop circuit prior to the application of ringing voltage to the conductive path. Photo coupled switching and monitoring circuits are used to coordinate application of ringing voltage with operation of a ring relay which completes the circuit path between the ringing voltage generator and the loop circuit.

Abstract: A circuit which overrides the initial rate circuit included in a coin telephone, to allow the central office to perform coin collect and refund operations independent of whether or not the initial rate has been deposited. This circuit operates in response to coin battery applied by the central office to operate a rate relay which connects the included coin relay to the central office.