OSCILLATOR CIRCUIT

An oscillator with noise rejection and a fifty percent duty cycle for the on-chip generation and conversion of a sine wave to a square wave, using an external reference crystal. The circuit comprises a low gain current switch including a first and second switching transistors (12, 14), with the control lines of the switching transistors connected to a reference voltage line (38). The reference crystal is connected across the control input (22) and the current receiving (23) terminals of the first transistor so that a square wave is obtained at the current receiving terminal (25) of the second transistor. A threshold circuit (42, 44, 46, 48, 50) is included for adjusting the voltage of the square wave signal from the second transistor and applying the adjusted signal to a diode-coupled receiver circuit, which provides the output for the circuit. This oscillator circuit provides a double action noise immunity through the use of a low gain current switch to prevent noise amplification, in combination with a diode-coupled receiver which is affected by noise only during signal transitions. A duty cycle very close to fifty percent is realized by the circuit.