Apparatus and a method for driving an ultrasonic sensor

1. An apparatus for driving an ultrasonic sensor comprising:

a driving unit for providing a transmission pulse to the ultrasonic sensor to transmit an ultrasonic wave and for receiving an ultrasonic echo for the ultrasonic wave;

an amplifier for amplifying an electrical signal for the ultrasonic echo;

an analog-to-digital converter for converting the amplified electrical signal into an original digital signal;

a signal processing unit for performing envelope-extraction-processing on the original digital signal and generating an envelope-extraction-processed signal; and

a control unit for outputting a distance between the ultrasonic sensor and an external object based on the original digital signal and the envelope-extraction-processed signal,

wherein the control unit monitors a frequency or phase change of vibration of a transducer of the ultrasonic sensor based on the original digital signal at least during a second period and analyses the envelope-extraction-processed signal during at least a third period provided that there are a first period in which the transducer is vibrated according to the transmission pulse, the second period in which the transducer is self-vibrated after the provision of the transmission pulse is stopped, and the third period in which the transducer stops the self-vibration, and

wherein the control unit outputs the distance between the ultrasonic sensor and the external object determined based on a time of flight between an initial detecting time and a transmission time of the ultrasonic wave, the initial detecting time being determined when the frequency or phase change of the transducer of the ultrasonic sensor is initially detected during the second period and the ultrasonic echo is received within a predetermined time.

2. The apparatus of claim 1 , wherein a frequency of the transmission pulses is in the middle of a resonance frequency and an anti-resonance frequency of the transducer.

3. The apparatus of claim 1 , wherein a self-vibration frequency of the transducer during the second period is a resonance frequency of the transducer.

4. The apparatus of claim 1 , wherein the control unit includes a memory for storing the time of flight between the initial detecting time and the transmission time of the ultrasonic wave.

5. The apparatus of claim 1 , wherein the control unit includes a phase or frequency change detecting unit that detects the phase or frequency change of the transducer.

6. A method for driving an ultrasonic sensor comprising:

providing a transmission pulse to the ultrasonic sensor to transmit an ultrasonic wave and for receiving an ultrasonic echo for the ultrasonic wave;

amplifying an electrical signal for the ultrasonic echo;

converting the amplified electrical signal into an original digital signal;

performing envelope-extraction-processing on the original digital signal and generating an envelope-extraction-processed signal; and

outputting a distance between the ultrasonic sensor and an external object based on the original digital signal and the envelope-extraction-processed signal,

wherein the outputting the distance includes:

monitoring a vibration frequency of a transducer of the ultrasonic sensor based on the original digital signal at least during a second period and analyzing the envelope-extraction-processed signal during at least the third period provided that there are a first period in which the transducer is vibrated according to the transmission pulse, the second period in which the transducer is self-vibrated after the provision of the transmission pulse is stopped, and the third period in which the transducer stops the self-vibration; and,

outputting the distance between the ultrasonic sensor and the external object determined based on a time of flight between an initial detecting time and a transmission time of the ultrasonic wave, the initial detecting time being determined when a change of the vibration frequency of the transducer is initially detected during the second period and the ultrasonic echo is received within a predetermined time.

7. The method of claim 6 , wherein a frequency of the transmission pulses is in the middle of a resonance frequency and an anti-resonance frequency of the transducer.

8. The method of claim 6 , wherein the vibration frequency of the transducer during the second period is a resonance frequency of the transducer.

9. The method of claim 6 , wherein the control unit includes a memory for storing the time of flight between the initial detecting time and the transmission time of the ultrasonic wave.

10. The method of claim 6 , wherein the change of the vibration frequency is detected based on a phase or frequency change of the transducer.