Electronic device, electrostatic capacitance sensor and touch panel

• US 10,330,766 B2
• Filed: 08/30/2011
• Issued: 06/25/2019
• Est. Priority Date: 08/30/2011
• Status: Active Grant

• Current Assignee: Tianma Microelectronics Company Limited
• Original Assignee: NLT Technologies, Ltd.
• Inventors: Haga, Hiroshi, Asada, Hideki
• Primary Examiner(s): Le, Son T
• Assistant Examiner(s): Zakaria, Akm
• Application Number:
  US14/240,675
• Publication Number:
  US 20150042357A1
• Time in Patent Office: 2,856 Days
• Field of Search: 324601, 345173
• CPC Class Codes: G01R 35/00 Testing or calibrating of apparatus covered by the other groups of this subclass
• CPC Class Codes: G06F 3/04182 Filtering of noise external to the device and not generated by digitiser components
• CPC Class Codes: G06F 3/0444 using a single conductive element covering the whole sensing surface, e.g. by sensing the electrical current flowing at the corners
• CPC Class Codes: G06F 3/0447 Position sensing using the local deformation of sensor cells

Abstract

When the excitation frequency of a touch panel and the frequency of external noise match or are close, noise cannot be removed by a bandpass filter. In addition, when a touch detection operating period is limited to a short period such as the no addressing period, the signal-to-noise ratio (S/N) decreases because frequency separation decreases and the noise removal effect by averaging is degraded. An electronic device of the present invention includes a sensor system (101), an excitation generator (102) that generates an intermittent sinusoidal signal and applies this signal to the sensor system, and a demodulator (105) that demodulates the amplitude modulated signal that is the output of the sensor system. The demodulator uses both the response x1(t) of the sensor system in the period in which the excitation generator outputs the sinusoidal signal, and the response z1(t) of the sensor system in the period in which the excitation generator does not output the sinusoidal signal at least either immediately before or immediately after the signal output to generate the demodulated signal D(t).

Claims

1. An electrostatic capacitance sensor comprising:

an excitation generator configured to generate an intermittent sinusoidal wave signal;

a sensor system configured to perform an arithmetic operation on an input and the intermittent sinusoidal wave signal, and to generate an amplitude-modulated signal having an amplitude which changes in accordance with the input and having a frequency which is equal to a frequency of the intermittent sinusoidal wave signal;

a demodulator configured to demodulate the amplitude-modulated signal by using both of;

a first observed signal that is the amplitude-modulated signal generated by the sensor system in a period in which the excitation generator has output a sinusoidal wave and of a second observed signal that is the amplitude-modulated signal generated by the sensor system in a period in which there is no sinusoidal wave output from the excitation generator, the period being at least one of immediately before and immediately after the period in which the excitation generator has output the sinusoidal wave; and

a resistive sheet,

wherein the sensor system includes drive and sensing circuitry connected to the resistive sheet, the drive and sensing circuitry being configured to apply a voltage generated by the excitation generator generating the intermittent sinusoidal wave signal to the resistive sheet and measure a current flowing through the resistive sheet,

capacitance of a capacitor formed by the resistive sheet and a pointing object is detected to detect a touch of the pointing object or coordinates of a touch of the pointing object, and

the demodulator is further configured to perform subtraction between a first vector representing the first observed signal and a second vector representing the second observed signal and to set a magnitude of a vector obtained by the subtraction as an amplitude of a true signal in response to the input, where the first vector is a vector having, as a first component and a second component respectively, a real part and an imaginary part of a frequency component of the sinusoidal wave in first complex signals generated by Fourier transform of the first observed signal representing the true signal and a noise, and the second vector is a vector having, as a first component and a second component respectively, a real part and an imaginary part of a frequency component of the sinusoidal wave in second complex signals generated by Fourier transform of the second observed signal representing the noise.

2. The electrostatic capacitance sensor according to claim 1, further comprising a display,

wherein in a non-addressing period of the display, there is a period in which the excitation generator outputs a sinusoidal wave and a period in which the excitation generator outputs no sinusoidal wave.

3. A touch panel comprising:

an excitation generator configured to generate an intermittent sinusoidal wave signal and provide the intermittent sinusoidal wave signal to the sensor system;

a sensor system configured to perform an arithmetic operation on an input and the intermittent sinusoidal wave signal, and to generate an amplitude-modulated signal having an amplitude which changes in accordance with the input and having a frequency which is equal to a frequency of the intermittent sinusoidal wave signal;

a demodulator configured to demodulate the amplitude-modulated signal by using both of;

a first observed signal that is the amplitude-modulated signal generated by the sensor system in a period in which the excitation generator has output a sinusoidal wave and of a second observed signal that is the amplitude-modulated signal generated by the sensor system in a period in which there is no sinusoidal wave output from the excitation generator, the period being at least one of immediately before and immediately after the period in which the excitation generator has output the sinusoidal wave; and

a resistive sheet,

wherein the sensor system includes drive and sensing circuitry connected to the resistive sheet, the drive and sensing circuitry being configured to apply a voltage generated by the excitation generator generating the intermittent sinusoidal wave signal to the resistive sheet and measure a current flowing through the resistive sheet,

capacitance of a capacitor formed by the resistive sheet and a pointing object is detected to detect a touch of the pointing object or coordinates of a touch of the pointing object, and

the demodulator is further configured to perform subtraction between a first vector representing the first observed signal and a second vector representing the second observed signal and to set a magnitude of a vector obtained by the subtraction as an amplitude of a true signal in response to the input, where the first vector is a vector having, as a first component and a second component respectively, a real part and an imaginary part of a frequency component of the sinusoidal wave in first complex signals generated by Fourier transform of the first observed signal representing the true signal and a noise, and the second vector is a vector having, as a first component and a second component respectively, a real part and an imaginary part of a frequency component of the sinusoidal wave in second complex signals generated by Fourier transform of the second observed signal representing the noise.

4. The touch panel according to claim 3, further comprising a display,

wherein in a non-addressing period of the display, there is a period in which the excitation generator outputs a sinusoidal wave and a period in which the excitation generator outputs no sinusoidal wave.

5. An electronic device comprising:

a sensor system including an operational amplifier and a resistor connected between an output terminal and an inverting input terminal of the operational amplifier;

a conductor connected to the inverting input terminal of the operational amplifier;

an excitation generator configured to generate an intermittent sinusoidal wave signal and provide the intermittent sinusoidal wave signal to a non-inverting input terminal of the operational amplifier; and

a demodulator,

wherein the sensor system is further configured to perform an arithmetic operation on an input and the intermittent sinusoidal wave signal, and to generate an amplitude-modulated signal having an amplitude which changes in accordance with the input and having a frequency which is equal to a frequency of the intermittent sinusoidal wave signal,

the demodulator is further configured to demodulate the amplitude-modulated signal by using both of;

a first observed signal that is the amplitude-modulated signal generated by the sensor system in a period in which the excitation generator has output a sinusoidal wave; and

a second observed signal that is the amplitude-modulated signal generated by the sensor system in a period in which there is no sinusoidal wave output from the excitation generator, the period being at least one of immediately before and immediately after the period in which the excitation generator has output the sinusoidal wave, capacitance of the conductor is detected, and

the demodulator is further configured to perform subtraction between a first vector representing the first observed signal and a second vector representing the second observed signal and to set a magnitude of a vector obtained by the subtraction as an amplitude of a true signal in response to the input, where the first vector is a vector having, as a first component and a second component respectively, a real part and an imaginary part of a frequency component of the sinusoidal wave in first complex signals generated by Fourier transform of the first observed signal representing the true signal and a noise, and the second vector is a vector having, as a first component and a second component respectively, a real part and an imaginary part of a frequency component of the sinusoidal wave in second complex signals generated by Fourier transform of the second observed signal representing the noise.

6. A method of demodulating a signal, comprising:

generating an intermittent sinusoidal wave signal by an excitation generator;

performing an arithmetic operation on an input and the intermittent sinusoidal wave signal to generate an amplitude-modulated signal having an amplitude which changes in accordance with the input and having a frequency which is equal to a frequency of the intermittent sinusoidal wave signal; and

demodulating the amplitude-modulated signal by using both of;

a first observed signal that is the amplitude-modulated signal generated in a period in which the excitation generator has output a sinusoidal wave; and

a second observed signal that is the amplitude-modulated signal generated in a period in which there is no sinusoidal wave output from the excitation generator, the period being at least one of immediately before and immediately after the period in which the excitation generator has output the sinusoidal wave,

wherein the demodulating step includes performing subtraction between a first vector representing the first observed signal and a second vector representing the second observed signal by subtracting each component between the first vector and the second vector and to set a magnitude of a vector obtained by the subtraction as an amplitude of a true signal in response to the input, where the first vector is a vector having, as a first component and a second component respectively, a real part and an imaginary part of a frequency component of the sinusoidal wave in first complex signals generated by Fourier transform of the first observed signal representing the true signal and a noise, and the second vector is a vector having, as a first component and a second component respectively, a real part and an imaginary part of a frequency component of the sinusoidal wave in second complex signals generated by Fourier transform of the second observed signal representing the noise.