Time-varying template for improved short-distance performance in coded ultrasonic ranging

A method of ultrasonic ranging comprising:

• emitting from an ultrasonic transducer a coded ultrasonic acoustic burst signal coded with a code;
• transducing, by the ultrasonic transducer or another ultrasonic transducer, a reflected acoustic signal coded with the code;
• generating a time-varying receive template characterizing the code, the length of the receive template being based on a time index measured from the start of emission of the burst signal;
• correlating the transduced reflected acoustic signal with the time-varying receive template to produce a correlated signal;
• and
• computing, based on the correlated signal, a time of flight of the reflected acoustic signal, the time of flight being indicative of a distance between the ultrasonic transducer and a detected object.

An ultrasonic detection system comprising:

• excitation circuitry configured to induce an ultrasonic transducer to emit a coded ultrasonic acoustic burst signal, coded with a code;
• listening circuitry configured to the receive from the ultrasonic transducer or another ultrasonic transducer a transduced reflected acoustic signal coded with the code;
• a time-varying template generator configured to generate a time-varying receive template characterizing the code, based on a time index measured from the start of emission of the burst signal;
• a correlator coupled to the listening circuitry and to the time-varying template generator and configured to correlate the transduced reflected signal with the time-varying receive template to produce a correlated signal;
• and
• time-of-flight circuitry coupled to the correlator and configured to compute a time of flight of the reflected acoustic signal based on the correlated signal, the time of flight being indicative of a distance between the ultrasonic transducer and a detected object;
• the time-varying template generator being configured to generate the time-varying receive template further based on a full-length template that is generated by sampling acoustic output of the coded ultrasonic acoustic burst signal including a period of transducer ringing that follows the end of the acoustic burst signal.

An ultrasonic detection system comprising:

• excitation circuitry configured to induce an ultrasonic transducer to emit a coded ultrasonic acoustic burst signal, coded with a code;
• listening circuitry configured to the receive from the ultrasonic transducer or another ultrasonic transducer a transduced reflected acoustic signal coded with the code;
• a time-varying template generator configured to generate a time-varying receive template characterizing the code, based on a time index measured from the start of emission of the burst signal;
• a correlator coupled to the listening circuitry and to the time-varying template generator and configured to correlate the transduced reflected signal with the time-varying receive template to produce a correlated signal;
• time-of-flight circuitry coupled to the correlator and configured to compute a time of flight of the reflected acoustic signal based on the correlated signal, the time of flight being indicative of a distance between the ultrasonic transducer and a detected object;
• and
• a time-varying gain multiplier coupled between the correlator and the time-of-flight circuitry and configured to adjust a gain of the correlated signal based on the time index.