| CPC A61B 8/0858 (2013.01) [A61B 8/5269 (2013.01); A61B 8/58 (2013.01); G06V 40/1306 (2022.01)] | 12 Claims |
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1. A ultrasonic image sensor, wherein the ultrasonic image sensor is coupled to a sinusoidal pulse signal generating circuit, the ultrasonic image sensor and the sinusoidal pulse signal generating circuit provided below a cover plate, the ultrasonic image sensor is configured to sense a surface pattern of object to be measured that makes contact with the cover plate from above the cover plate, the ultrasonic image sensor comprises:
an upper electrode, coupled to the sinusoidal pulse signal generating circuit;
a lower electrode array, including a first lower electrode;
a piezoelectric layer, provided between the upper electrode and the lower electrode array, wherein the piezoelectric layer is excited by means of a sinusoidal pulse signal generated by the sinusoidal pulse signal generating circuit so as to generate ultrasonic wave, the ultrasonic wave is transmitted along the cover plate to the object to be measured and then a reflected echo is generated, and the reflected echo along the cover plate is transmitted back to the piezoelectric layer, so that the piezoelectric layer generates a receiving signal; and
a detection circuit array, including a first detection circuit, coupled to the first lower electrode and configured to determine amplitude of the receiving signal, wherein the first detection circuit comprises:
an operational amplifier, having a positive end, a negative end and an output end, wherein the output end is configured to output a sensing result of the ultrasonic image sensor;
a capacitor unit, coupled between the output end and the negative end of the operational amplifier;
a reset switch, arranged in parallel with the capacitor unit;
a first switch, coupled between a reference voltage and the first lower electrode; and
a second switch, coupled between the first lower electrode and the negative end of the operational amplifier,
wherein in a general phase that the reset switch is turned off, after n pulse periods of the sinusoidal pulse signal, a voltage at the output end of the operational amplifier is successively accumulated n times, where n is a positive integer,
wherein each pulse period of the sinusoidal pulse signal includes a first time period and second time period, wherein in the first time period, the sinusoidal pulse signal includes N sinusoidal waves, each having a period equal to t, and N is a positive integer, wherein in the second time period, the sinusoidal pulse signal has a fixed voltage, and the first detection circuit detects the receiving signal according to each pulse period,
wherein:
in a reset phase, the reset switch is turned on and the second switch is turned off, the output end of the operational amplifier outputs the reference voltage; and
in the general phase, the reset switch is turned off, and the receiving signal at least includes N waves, each having a period equal to t, wherein the N waves correspond to one of the n pulse periods of the sinusoidal pulse signal, wherein in each period of the N waves, the first detection circuit is set to a sampling mode for a time period equal to t*R and is set to a non-sampling mode for a time period equal to t*(1−R), wherein R is greater than 0 and is smaller than 1, wherein:
in the sampling mode, the first switch is turned off and the second switch is turned on, so that amplitude change of the receiving signal during the sampling mode is reflected in a specific proportion and is accumulated at the output end of the operational amplifier; and
in the non-sampling mode, the first switch is turned on and the second switch is turned off, so that the amplitude change of the receiving signal generated by the piezoelectric layer in the non-sampling mode does not respond and does not accumulate at the output end of the operational amplifier, so that the voltage at the output end of the operational amplifier remains constant in the non-sampling mode.
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