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Ultrasonic receiving circuit

  • US 8,514,075 B1
  • Filed: 03/21/2011
  • Issued: 08/20/2013
  • Est. Priority Date: 03/22/2010
  • Status: Active Grant
First Claim
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1. An ultrasonic occupancy sensor for detecting presence or absence of an occupant in a space, the occupancy sensor comprising:

  • an ultrasonic transmitting circuit comprising an ultrasonic transmitting element for transmitting ultrasonic waves;

    an ultrasonic receiving circuit comprising an ultrasonic receiving element for receiving ultrasonic waves and generating an ultrasonic input signal, an amplifier circuit for amplifying the amplified signal to generate an amplified signal, a synchronous rectifier for rectifying the input signal to generate a rectified signal, and a filter for filtering the rectified signal to generate a filtered signal, the synchronous rectifier comprising a non-inverting amplifier and an inverting amplifier both receiving the amplified signal, the synchronous rectifier further comprising a first analog switch coupled to an output of the non-inverting amplifier and a second analog switch coupled to an output of the inverting amplifier, the first and second analog switches electrically coupled together for forming the rectified signal; and

    a controller operable to drive the ultrasonic transmitting circuit with a drive signal to control an ultrasonic transmission frequency of the transmitted ultrasonic waves, the controller operable to render the first and second analog switches conductive and non-conductive on a complementary basis such the outputs of the analog switches are mixed together to form the rectified signal, the controller further operable to receive the filtered signal and to determine that the space is occupied if a magnitude of the filtered signal exceeds a threshold.

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