Abstract: A relaxation oscillator which is suited for fabrication as a monolithic circuit and which uses a parallel resistive capacitive frequency determining network wherein a capacitor is charged and discharged between an upper and lower voltage level. As the capacitor is charged to a potential exceeding a first threshold voltage level supplied to a comparator switch, the operating state of the comparator is caused to switch. A current detecting circuit is included which is rendered responsive to a current supplied thereto from a charge circuit when the capacitor is charged substantially to the upper voltage level. The current detecting circuit thereafter actuates a control circuit for switching the threshold voltage applied to the comparator from the first level to a second lower level.

Abstract: A direction phase shift keyed communication system provides the capacity to transmit any one of two symbols for each modulation level. The modulator produces a substantially constant frequency signal which includes a phase transistion in respect of each information bit. In a system with a single modulation level, corresponding to a phase transistion .phi., one of the two symbols is represented by a phase transition +.phi., i.e., an advancing phase transition. The other symbol is represented by a phase transition -.phi., i.e., a retarding phase transition. A demodulator responds to a substantially constant frequency signal with a phase transition included, and produces an output signal of a first kind in response to an advancing phase transition +.phi. and an output signal of a second kind in response to a retarding phase transistion -.phi.. The system is capable of operating with multiple modulation levels, each of which can represent any one of two symbols, depending on the sense, i.e.