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

Abstract

Ultrasonic ranging systems and methods that emit coded bursts and correlate transduced acoustical echoes of the bursts with a receive template characterizing a burst code to determine time-of-flight information use receive templates of time-variable length to improve short-range object detection. The template length is based on a time index measured from the start of the burst emission. The detection can account for a dead zone of transducer ringing following a burst. A time-variable gain that is also based on the time index can be applied to the correlated signal. The length and gain can be adjusted with reduced temporal frequency to reduce computation cost.

What is claimed is: 
     
         1 . An ultrasonic ranging system comprising:
 time-varying template generation circuitry configured to generate a time-varying coded receive template based on a full-length template and a time index from a start of a burst signal provided to an ultrasonic transducer, the length of the time-varying coded receive template depending on the time index; and   correlator circuitry coupled to the time-varying template generation circuitry and configured to correlate a received transduced reflected signal with the time-varying coded receive template to produce a correlated signal, an envelope of the correlated signal containing a peak indicative of a distance between the ultrasonic transducer and a detected object.   
     
     
         2 . The system of  claim 1 , further comprising a time-varying gain multiplier coupled to the correlator circuitry and configured to adjust a gain of the correlated signal in an amount that is based on the time index from the start of the burst signal. 
     
     
         3 . The system of  claim 1 , the time-varying template generation circuitry being configured to generate the time-varying coded receive template further based on a programmable dead zone duration parameter indicative of a period of transducer ringing that follows the end of the burst signal. 
     
     
         4 . The system of  claim 1 , the time-varying template generation circuitry being configured to re-generate the time-varying coded receive template with a frequency that is less than once every sample. 
     
     
         5 . 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.   
     
     
         6 . The method of  claim 5 , the time-varying receive template being generated further based on a full-length template that is resampled from a coded excitation signal at point prior to its transduction into the coded ultrasonic acoustic burst signal. 
     
     
         7 . The method of  claim 5 , further comprising adjusting a gain of the correlated signal based on the time index. 
     
     
         8 . 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.   
     
     
         9 . 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.