Abstract: Digital noise detection circuit for detecting the presence of noise in digital diphase data and for producing an alarm signal in response to the detection of such noise. The digital diphase data is applied to circuitry from which a clock signal is extracted and processed to derive a first input signal at a first input of an alarm NAND logic gate. The clock signal is also employed by a digital phase lock loop circuit to produce a second signal at a second input of the alarm NAND logic gate which, in the absence of noise corrupting or otherwise affecting the diphase data, is out of phase with the signal at the first input of the alarm NAND logic gate. As a result, no alarm signal is produced by the alarm NAND logic gate.

Abstract: An essential user bypass circuit for use in switch units of a telephone switching system. Telephone subscribers at each switch unit are able to communicate with each other and with subscribers at other switch units via associated subscriber apparatus and trunk group lines interconnecting the switch units. All call processing operations, including the formation of "from-to" address signals for connecting subscribers with each other and with trunk group lines, are normally controlled by a processor unit (containing dual processors) at each switch unit.

Abstract: A master timing generator capable of tracking an externally generated clock signal and of maintaining desired operation during periods of disruption or perturbation of the clock signal by noise or other high-energy disturbances. The master timing generator includes a voltage controlled oscillator controlled by an input dc control voltage to produce an output signal which is maintained in a particular phase relationship with the clock signal by phase lock loop circuitry coupled to the oscillator. A dc standby voltage signal representative of the value of the control voltage applied to the oscillator is retained during operation of the master timing generator in a standby unit which, in the absence of noise affecting the clock signal, is electrically uncoupled from the oscillator.