Signal detector and method for detecting signals having selected frequency characteristics

Abstract

A signal detector and signal detection methodology is provided to monitor oscillatory signals, such as sound signals, to produce detector output in response to the presence of target signals having a frequency within a selected frequency range, such as ultrasonic sound signals. The detector has input processing circuitry that receives the oscillatory signals and filters out those which do not fall within the selected frequency range to produce an input signal. The input signal is split into two components, a primary input component and a control component. The primary input component is amplified proportionally to the amplitude of the control component. Preferably, the primary input component is processed to produce a clean, stable intermediate signal. Here, the signal detector provides processing circuitry that passes primary input components that have amplitudes exceeding a threshold, to eliminate low level noise; the primary input components are variably amplified inversely to the amplitude thereof to produce an initial intermediate signal having a substantially uniform amplitude at the frequency of the input signal. This initial intermediate signal is processed by a Schmitt-Trigger to create a square-wave signal. The processing circuit includes a scaler sub-circuit to divide the square-wave signal by an integer, and an integrating sub-circuit integrates the resulting scaled signal to produce the intermediate signal. An amplification circuit has variable gain controlled by averaging the amplitude of the input signal by way of the control component so that the intermediate signal is amplified according to the original amplitude to produce a scaled replica of the filtered input signal. Sensitivity adjustment and visual and audible displays are used for the detector output.

Dependencies are inferred from the claim text.