Abstract: An encryption system is provided for interfacing a time division multiplexing (TDM) telecommunications arrangement with an encryption device for the scrambling of data received by the telecommunications arrangement. The telecommunications arrangement produces a TDM data stream formatted into TDM frames including a predetermined number of TDM framing bits and corresponding framing bit locations. At a local side of the system, a first TDM data stream is received and sampled, and the TDM framing bit information is detected and stored therefrom. The data stream is then sent to an encryptor for encryption, and thereafter the TDM framing bit information is reinserted into the corresponding bit locations of the encrypted data stream. As a result, the TDM framing bit information is passed around the encryptor. This encrypted data stream and framing bit information is transmitted to a remote station across a TDM (e.g., T1) communications network.

Abstract: An input voltage is converted into a logarithmic representation thereof by exponentially changing the charge of a capacitor, producing pulses at a rate dependent upon the time taken for the charge to change between the two reference voltages, and counting the pulses during the time taken for the charge to change between the input voltage and a reference voltage, whereby the conversion is independent of the precise time constant governing the exponential change. The pulses can be produced under the control of a phase-locked loop, or by frequency-dividing clock pulses by a count which has been previously established by frequency-dividing the same clock pulse frequency by a predetermined factor. The conversion can be effected rapidly and accurately for input voltages within a relatively large range, without using high-precision components.

Abstract: Apparatus is disclosed for automatically measuring accurately and rapidly alternating and direct voltages, resistance, and capacitance of a telephone line. Direct voltages and relatively high resistances can be determined by filtering out 60 Hz a.c. signals and measuring line current with and without a voltage source connected in series with the line. Capacitance is measured by charging the line from the voltage source, discharging the line into a plurality of integrators having different time constants, and sampling the output voltage of one of the integrators after a respective integral number of 60 Hz periods. The integrator whose output voltage is sampled depends on the capacitance being measured. The resultant measurement is corrected in respect of voltages on the line by performing a second integration without again charging the line, and the corrected result is modified to take into account the previously measured resistance of the line.

Abstract: Offset voltages of a precision rectifier circuit, buffer amplifiers, and an input comparator of a log converter are compensated for by charging a coupling capacitor to the combined total offset voltage of the apparatus. The charging is effected by causing the comparator to operate as a unity gain inverting amplifier during part of the operating cycle of the log converter when the comparator output signal is not used, so that the log converter operation is not adversely affected. During such charging the input of the precision rectifier circuit, to which the a.c. input signal is normally applied, is grounded. Throughout the charging and associated switching operations a capacitor of a smoothing filter connected following the precision rectifier circuit is disconnected from ground to isolate the smoothing filter output from ground and to prevent switching transients from affecting the charge of this capacitor.

Abstract: A precision rectifier circuit includes two differential amplifiers each having a negative feedback path including a diode. Two pnp transistors have their base-emitter paths connected in parallel with the respective diodes and their collectors connected together and via an output resistor to ground. An a.c. signal to be rectified is applied to non-inverting inputs of the amplifiers, whose inverting inputs are interconnected via a resistor in series with a capacitor, to develop a unipolar output voltage across the output resistor. The capacitor renders the output voltage independent of input offset voltages of the amplifiers. The transistors can comprise Darlington-connected transistors to avoid the need for matching.