Ultrasonic image sensor and related electronic device
The present application discloses an ultrasonic image sensor and a related electronic device. The ultrasonic image sensor is coupled to a sinusoidal pulse signal generating circuit. The ultrasonic image sensor and the sinusoidal pulse signal generating circuit are provided below a cover plate. The ultrasonic image sensor is used to sense a surface pattern of an object to be measured that makes contact with the cover plate from above the cover plate. The ultrasonic image sensor includes: an upper electrode; a lower electrode array; a piezoelectric layer, which is 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 an ultrasonic wave, the ultrasonic wave is transmitted along the cover plate to the object to be measured and then a reflected echo is generated.
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.
2 . The ultrasonic image sensor according to claim 1 , further comprising:
a control circuit, configured to control the sinusoidal pulse signal generated by the sinusoidal pulse signal generating circuit, and control the reset switch, the first switch and the second switch of the first detection circuit.
3 . The ultrasonic image sensor according to claim 1 , wherein the lower electrode array further comprises a second lower electrode, and the detection circuit array further comprises a second detection circuit, wherein a structure of the second detection circuit is the same as a structure of the first detection circuit, and the second detection circuit is coupled to the second lower electrode.
4 . The ultrasonic image sensor according to claim 1 , wherein R is ½, and:
the first detection circuit is set to the sampling mode during the time period equal to t*R when the N waves of the receiving signal drop from its peak to its trough; and
the first detection circuit is set to the non-sampling mode during the time period equal to t*(1−R) when the N waves of the receiving signal rise from its trough to its peak.
5 . The ultrasonic image sensor according to claim 4 , wherein capacitance of the capacitor unit is CI, capacitance of a parasitic capacitor of the piezoelectric layer is CS, a voltage difference between the peak and the trough of the N waves is 2*VA, and the N waves drop from its peak to its trough, so that the voltage at the output end of the operational amplifier increases by 2*N*VA*CS/CI.
6 . The ultrasonic image sensor according to claim 1 , wherein the positive end of the operational amplifier is coupled to a third calibration voltage.
7 . The ultrasonic image sensor according to claim 1 , further comprising:
a shielding electrode, provided below the first lower electrode, wherein the shielding electrode is coupled to a direct current voltage, and the shielding electrode is configured to shield a noise coupled to the first lower electrode.
8 . An electronic device, comprising:
the ultrasonic image sensor according to claim 1 ;
the sinusoidal pulse signal generating circuit; and
the cover plate.
9 . The electronic device according to claim 8 , further comprising a display screen, wherein the cover plate is provided at one side of the display screen, and the ultrasonic image sensor and the sinusoidal pulse signal generating circuit are provided at another side of the display screen.
10 . The electronic device according to claim 9 , wherein the display screen allows sound waves to pass through.
11 . A ultrasonic image sensor, wherein the ultrasonic image sensor is coupled to 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 and a second 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;
a second switch, coupled between the first lower electrode and the negative end of the operational amplifier;
a third switch, coupled between the reference voltage and the second lower electrode; and
a fourth switch, coupled between the second lower electrode and the negative end of the operational amplifier.
12 . A ultrasonic image sensor, wherein the ultrasonic image sensor is coupled to 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;
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, and the positive end of the operational amplifier is coupled to a reference voltage;
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 the 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;
a calibration electrode, provided below the first lower electrode;
a first calibration switch, coupled between the calibration electrode and a first calibration voltage, wherein a conduction state of the first calibration switch is synchronized with the first switch; and
a second calibration switch, coupled between the calibration electrode and a second calibration voltage, wherein a conduction state of the second calibration switch is synchronized with the second switch;
wherein the calibration electrode, the first calibration switch, and the second calibration switch are configured to offset a static noise at the output end of the operational amplifier.