Abstract: A crystal oscillator in a bridge circuit coupled to a differential amplifier. Coordinated adjustment of one or two arms of the bridge permits pulling of the crystal's operating frequency both above and below its series resonant frequency.

Abstract: The oscillator circuit comprises an amplifier having a pair of inputs, a positive feedback path producing a positive feedback ratio to one of the inputs, and a negative feedback path including a series resonant circuit producing a negative feedback ratio to the other of the inputs. The positive and negative feedback paths are independent such that the current in each of the paths can be adjusted independently. In this manner, a high Q multiplier effect is achieved. Also, the circuit has an output path which is separate from the input path so that a high output signal level can be achieved while maintaining a low current through the series resonant circuit.

Abstract: The data selection circuit includes a multiplexer circuit which receives a plurality of inputs and individually connects each of the inputs to an output line. The multiplexer is sequenced by signals from a timing circuit which causes inputs having a higher signal level to be connected to the multiplexer output for a greater length of time. The data selection circuit is particularly suitable for enhancing the image on a CRT of a continuous tone frequency modulated sonar system.