Abstract: An ultrasonic sensor system (36) has a transducer (40) that emits an ultrasonic signal (54), in response to an electrical excitation signal (52) from driver/receiver circuitry (42), and outputs an electrical response signal (58), in response to receipt of a reflected ultrasonic signal (56) from an object, such as a vehicle occupant (14). The response signal (58) is an oscillating signal that has a voltage amplitude indicative of the strength of the reflected ultrasonic signal (56). A receiver circuit (68) of driver/receiver circuitry (42) processes the response signal (58) from said transducer (40) and outputs an analog, non-oscillating signal (60). The analog signal (60) has a voltage amplitude indicative of the voltage of the electrical response signal (58). A comparator (84) of a comparator preprocessor (44) compares the voltage of the analog signal (60) to a predetermined reference voltage (VREF1) and outputs a digital signal (38).

Abstract: An apparatus (52) senses the presence of a rearward facing child restraint seat (34) in a vehicle. Signal generating components (80, 84 and 90) of a driver/receiver circuit (64) provide an electrical transmit signal, at a first frequency, which is applied to an antenna (60) and the antenna transmits an electromagnetic (EM) signal (62) at the first frequency during a first time period. During a second time period, a component (84) of the driver/receiver circuit (64) provides a signal at a second, different frequency. An identification tag (54) is securable to the child restraint seat (34) and provides an EM return signal (68) in response to the EM transmit signal (62). The antenna (60) receives the EM return signal (68) and provides an electrical return signal in response to the EM return signal. A mixer (122) is coupled to receive both the second frequency signal and the electrical return signal in the second time period, and provides a beat frequency signal.