TECHNICAL FIELD

The present invention relates to detection of pressure signals, and more specifically relates to a detection circuit and method that differentiate input signals, comprehend the signal characteristics based on the results, and then segment and output only an input signal from which a heat input signal (pyro signal) has been removed, so as to detect only pressure input signals (piezo signals) from among input signals supplied to a piezoelectric material.

BACKGROUND ART

Piezoelectric materials generate a relatively large force compared with their own weights and have a characteristic of quickly responding to a supplied voltage. With such characteristics, piezoelectric materials are applied to various industries. There are various components using these piezoelectric materials (in other words, the form of the piezoelectric material). Among them, a piezoelectric film is a material that is displaced when force is applied to both its ends, and a voltage is generated in proportion to the displacement. With such characteristics, piezoelectric films are widely used in piezoelectric generators, sensors, ultrasonic transmitters and receivers, and the like.

FIG. 1ais a diagram showing a piezoelectric film,FIG. 1bis a diagram showing the front end of a pressure sensor, andFIG. 1cis a diagram showing an output voltage signal according to input impedance R.

Referring toFIG. 1atoFIG. 1c, pressure sensing using a piezoelectric element is performed by discharging or integrating the charge generated in a piezoelectric film using an impedance adapter or a Miller's integrator in the front end. Among them, the impedance adapter has a characteristic that the output waveform changes according to input impedance R. Then, by integrating the output voltage signal corresponding to the input impedance R, signal information measured by the sensor can be obtained. However, the final signal information thus obtained includes input information of both pressure and heat. Previously, only physical pressure was measured without a pressure signal due to heat, or a method of absorbing heat using a specific substance to thereby reduce the influence of heat was used. However, these techniques are limited in that the heat input signals cannot be completely eliminated.

FIG. 2ais a graph showing the characteristics of a piezoelectric element on a temperature basis, andFIG. 2bis a graph showing the characteristics of a piezoelectric element on humidity basis.FIG. 3ais a diagram showing a pressure input signal from which a heat input signal is removed, andFIG. 3bis a diagram showing both a heat input signal and a pressure input signal.

Pressure sensing is used mainly for touch sensing through a human finger; at this time, input information due to heat is also displayed because of a temperature difference between the finger and the piezoelectric element.

FIGS. 3aand 3bshow more specific characteristics of the pressure input signal and the heat input signal. Referring toFIG. 3a, the pressure input signal has characteristics that an input signal upon touching (touch down (pressing)) is output as a positive value, and an input signal upon release (touch up (releasing)) is output as a negative value. Referring toFIG. 3b, there is a difference in output speed between the pressure input signal and the heat input signal. This is because the conduction speed of the temperature input signal is relatively longer (slower) than the conduction speed of the pressure input signal.

CITATION LIST

Patent Documents

Patent Document 1: Japanese Patent No. 6098730

Patent Document 2: Japanese Patent No. 6106011

Patent Document 3: Specification of Published U.S. Patent Application No. 2017/0033276

SUMMARY OF INVENTION

Technical Problem

Therefore, the present invention was proposed in consideration of the various conditions as described above, and an object of the present invention to remove the heat input signal by using the difference in the speed of supplying the pressure input signal and the heat input signal and the differential information, thereby outputting only the pressure input signal.

An object of the present invention is to significantly reduce the influence on the thermal reaction as compared with the prior art, and to increase the reaction speed of the input terminal at the front end, thereby enabling detection of a pressure signal at a higher speed.

Another object of the present invention is to output a signal having a superior thermal reaction attenuation effect compared with the use of an additional process for heat absorption when a piezoelectric material is produced.

The objects of the present invention are not limited to those mentioned above, and unmentioned or other objects would clearly be understood by those skilled in the art from the following descriptions.

Solution to Problem

As described above, examples of a component using a piezoelectric material (in other words, the form of the piezoelectric material) include a piezoelectric film.

The present invention regarding piezoelectric film is explained in detail below. Based on common technical knowledge, the description below also applies to components or forms other than a piezoelectric film.

In order to achieve the above objects, the pressure signal detection circuit in which a pyroelectric signal from a piezoelectric film is suppressed according to the technical idea of the present invention is constituted of a signal processing unit for receiving input of an input signal from a piezoelectric film, a differentiator for differentiating the input signal for the analysis of the signal component of the input signal, a signal processing unit for outputting an analysis value of the signal component of the input signal based on the differential value of the differentiator, an offset removal unit for removing offset of the input signal using the signal component analysis value, and an integrating unit for integrating the input signal to output a pressure input signal value in which a heat input signal value is deleted.

The pressure signal detection circuit is characterized by further comprising a filter unit constituted of a low-pass filter (LPF) and a moving average filter (MAF) for removing noise of the input signal supplied from the signal input unit.

The signal processing unit is characterized by comparing the differentiated input signal value with a preset threshold value to determine whether the input signal is a pressure input signal or a heat input signal. When the differentiated input signal value is equal to or greater than the preset threshold value, the input signal is determined to be a pressure input signal and the integrating unit is executed. When the differentiated input signal value is smaller than the preset threshold value, the input signal is determined to be a heat input signal, and the offset removal unit is executed.

When a pressure input signal during the reference time is not re-detected after the pressure input signal is detected from the differentiated input signal value, the signal processing unit outputs a reset signal for initializing the integrating unit.

When the pressure input signal is not detected from the differentiated input signal value in all sections, the signal processing unit outputs a reset signal for initializing the integrating unit.

The offset removal unit outputs a value obtained by subtracting the heat input signal from the input signal.

In order to achieve the object described above, the pressure signal detection method in which a pyroelectric signal from a piezoelectric film is suppressed according to the technical idea of the present invention is characterized by comprising a signal input step of receiving input of an input signal from a piezoelectric film from a signal processing unit, a differentiating step of differentiating the input signal for the analysis of the signal component of the input signal by an differentiator, a signal processing step of outputting a signal component analysis value of the input signal based on the differential value of the differentiator in a signal processing unit, an offset removal step of removing offset of the input signal using the signal component analysis value of the signal processing unit, and an integrating step of integrating the input signal in the integrating unit to output a pressure input signal value in which a heat input signal value is deleted.

The pressure signal detection method is characterized by further comprising a filter step of removing noise of the input signal in a filter unit so as to remove noise from the input signal supplied from the signal input step.

The signal processing step is characterized by comparing the differentiated input signal value with a preset threshold value to determine whether the input signal is a pressure input signal or a heat input signal. If the value of the differentiated input step is equal to or greater than the predetermined threshold value, the input signal is determined to be a pressure input signal and the integrating step is executed. If the differentiated input signal value is smaller than the predetermined threshold value, the input signal is determined to be a heat input signal, and the offset removal step is executed.

When a pressure input signal during the reference time is not re-detected after the pressure input signal is detected from the differentiated input signal value, the signal processing step outputs a reset signal for initializing the integrating unit (integrating step).

When the pressure input signal is not detected from the differentiated input signal value in all sections, the signal processing step outputs a reset signal for initializing the integrating unit (integrating step).

The offset removal step outputs a value obtained by subtracting the heat input signal from the input signal.

Advantageous Effects of Invention

The following is achieved with the above circuit and the method for detecting a pressure signal in which a pyroelectric signal is suppressed in the piezoelectric film.

First, an effect of outputting only pressure input signals is ensured by removing a heat input signal using a difference in input speed between the pressure input signal and the heat input signal, as well as differential information.

Second, an effect of significantly reducing the influence on the thermal reaction as compared with the prior art, increasing the reaction speed of the input terminal at the front end, thereby enabling detection of a pressure signal at a higher speed, is ensured.

Third, an effect of outputting a signal with a superior thermal reaction attenuation effect compared with the use of an additional process for heat absorption when a piezoelectric film is produced is ensured.

