Semiconductor device and ultrasonic sensor
A semiconductor device includes a driving circuit arranged to be capable of supplying a drive signal in an ultrasonic band to a piezoelectric element, a damping circuit having a resistance load and an inductive load, and a control circuit arranged to be capable of controlling the driving circuit and performing a reverberation reduction operation after stopping the supply of the drive signal to the piezoelectric element. In the reverberation reduction operation, the control circuit controls the driving circuit to supply the piezoelectric element with a damping signal having a phase different from that of the drive signal, and then enables the damping circuit to connect to the piezoelectric element.
1 . A semiconductor device comprising:
a driving circuit arranged to be capable of supplying a drive signal in an ultrasonic band to a piezoelectric element;
a damping circuit having a resistance load and an inductive load;
a control circuit arranged to be capable of controlling the driving circuit, so as to perform a reverberation reduction operation after stopping a supply of the drive signal to the piezoelectric element,
wherein in the reverberation reduction operation, the control circuit is configured to control the driving circuit to supply the piezoelectric element with a damping signal having a phase different from that of the drive signal, and to enable the damping circuit to connect to the piezoelectric element;
an adjustment driving circuit arranged to be capable of supplying the piezoelectric element with a second drive signal in the ultrasonic band separately from the drive signal as a first drive signal,
wherein the control circuit is arranged to be capable of performing an adjustment operation using the adjustment driving circuit, before a normal detection operation including the supply of the first drive signal to the piezoelectric element,
in the adjustment operation, the control circuit is configured to determine a set physical quantity for an adjustment target based on a reverberation state of the piezoelectric element after supplying the second drive signal to the piezoelectric element,
in the normal detection operation, the control circuit is configured to control the adjustment target to have the set physical quantity, and
the adjustment target includes at least one of a resistance value of the resistance load, an inductance value of the inductive load, and the phase of the damping signal,
wherein the adjustment driving circuit is arranged to be capable of supplying the piezoelectric element with a second damping signal having a phase different from that of the second drive signal, separately from a first damping signal as the damping signal,
the adjustment operation includes an adjustment unit operation,
in the adjustment unit operation, the control circuit is configured to supply the second drive signal to the piezoelectric element, stop the supply of the second drive signal, control the adjustment driving circuit to supply the second damping signal to the piezoelectric element, and then connect the damping circuit to the piezoelectric element, and
in the adjustment operation, the control circuit is capable of performing the adjustment unit operation a plurality of times while changing the adjustment target by a plurality of steps, and in each adjustment unit operation, the control circuit is configured to determine the set physical quantity based on the reverberation state of the piezoelectric element when the damping circuit is connected to the piezoelectric element.
2 . The semiconductor device according to claim 1 , further comprising a reception circuit arranged to be capable of receiving a signal in the ultrasonic band,
wherein the normal detection operation includes one or more detection unit operations,
in each of the detection unit operations, the first drive signal is supplied to the piezoelectric element, and after stopping the supply of the first drive signal, the reverberation reduction operation is performed,
in each adjustment unit operation of the adjustment operation, and in each detection unit operation of the normal detection operation, the control circuit detects a ringing time, which is time after the damping circuit is connected to the piezoelectric element until a voltage value proportional to amplitude of a received signal of the reception circuit becomes lower than a predetermined threshold value,
in the adjustment operation, the control circuit obtains and keeps the ringing time when the adjustment target has the set physical quantity, and
after starting the normal detection operation via the adjustment operation, if a relationship between the ringing time detected in the normal detection operation and the kept ringing time satisfies a predetermined restart condition, the control circuit is capable of starting the adjustment operation again.
3 . The semiconductor device according to claim 1 , wherein the control circuit is capable of performing the adjustment unit operation the plurality of times while changing the resistance value of the resistance load by the plurality of steps in the adjustment operation, determines a set resistance value for the resistance load based on the reverberation state of the piezoelectric element when the damping circuit is connected to the piezoelectric element in each adjustment unit operation, and controls the resistance load to have the set resistance value in the normal detection operation.
4 . The semiconductor device according to claim 1 , wherein the control circuit is capable of performing the adjustment unit operation the plurality of times while changing the inductance value of the inductive load by the plurality of steps in the adjustment operation, determines a set inductance value for the inductive load based on the reverberation state of the piezoelectric element when the damping circuit is connected to the piezoelectric element in each adjustment unit operation, and controls the inductive load to have the set inductance value in the normal detection operation.
5 . The semiconductor device according to claim 1 , wherein the control circuit is capable of performing the adjustment unit operation the plurality of times while changing a phase of the second damping signal viewed from the second drive signal by the plurality of steps in the adjustment operation, determines a set phase for the first damping signal based on the reverberation state of the piezoelectric element when the damping circuit is connected to the piezoelectric element in each adjustment unit operation, and controls the first damping signal to have the set phase in the normal detection operation.
6 . The semiconductor device according to claim 1 , wherein the second drive signal has a smaller amplitude than the first drive signal.
7 . The semiconductor device according to claim 1 , wherein the resistance load and the inductive load is connected in parallel in the damping circuit.
8 . An ultrasonic sensor comprising:
the semiconductor device according to claim 1 ; and
a piezoelectric element connected to the semiconductor device.