Ultrasonic signaling is used for proximity and obstacle detection, level sensing, sonars, and so forth. Such signal chains detect the amplitude of received ultrasonic signal at a particular center frequency. Figure 9-9 shows a high-gain narrow bandpass filter and peak detector circuit using any of the OPAx863 devices. The signal at the frequency of interest is filtered out, gained, and peak detected to report the amplitude at the output of this circuit. The phase information is lost in this circuit. The OPAx863 devices are used with its 50-MHz GBW to add a single-stage gain, and the peak detection capability is easily made with the RRIO capability of these amplifiers.