A circuit device includes a first PLL circuit to which a first clock signal having a first clock frequency generated using a first resonator and a reference clock signal are input, and which performs phase synchronization between the first clock signal and the reference clock signal, a second PLL circuit to which a second clock signal generated using a second resonator and having a second clock frequency different from the first clock frequency and the reference clock signal are input, and which performs phase synchronization between the second clock signal and the reference clock signal, and a time-to-digital conversion circuit adapted to convert time into a digital value using the first clock signal and the second clock signal.

A wideband sonar receiver is provided that includes: a selectable bandpass filter adapted to filter a received sonar signal to produce a filtered signal and a correlator adapted to correlate the baseband samples with baseband replica samples to provide a correlated signal. In addition, the wideband sonar receiver may include a shaping filter to shape unshaped received pulses. Finally, a variety of sonar processing algorithms are described with regard to reducing clutter and interference, target detection, and bottom detection.

A wideband sonar receiver is provided that includes: a selectable bandpass filter adapted to filter a received sonar signal to produce a filtered signal and a correlator adapted to correlate the baseband samples with baseband replica samples to provide a correlated signal. In addition, the wideband sonar receiver may include a shaping filter to shape unshaped received pulses. Finally, a variety of sonar processing algorithms are described with regard to reducing clutter and interference, target detection, and bottom detection.

A method and apparatus to gate an ultrasonic emitter operation includes a housing including the ultrasonic emitter, where the ultrasonic emitter is operable to periodically transmit an ultrasonic pulse of a predefined frequency. A microphone circuit is disposed in the housing, such that the microphone circuit is operable to receive a reflected ultrasonic signal derived from the transmitted ultrasonic pulse. A controller is coupled to the emitter and the microphone circuit, where the controller operable to gate the operation of the emitter to an OFF state based on at least one measured parameter of the reflected ultrasonic signal. The parameters can include a Doppler measurement and a distance measurement.