Semiconductor device

A switch group selectively outputs a signal input from IC terminals and a reference voltage. Another switch group selectively outputs a signal input from IC terminals and a reference voltage. A differential amplifier amplifies a differential voltage between a signal output from the switch group and a signal output from the another switch group. The switch group and the another switch group include the same number of switches. When to select any of signals input from the IC terminals in the switch group, a reference voltage is selected in the another switch group. When to select any of signals input from the IC terminals in the another switch group, a reference voltage is selected in the switch group.

CROSS-REFERENCE TO RELATED APPLICATIONS

The disclosure of Japanese Patent Application No. 2018-056353 filed on Mar. 23, 2018 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND

The present invention relates to a semiconductor device, and relates, for example, to a semiconductor device to which a sensor is coupled.

Japanese Unexamined Patent Application Publication No. 2017-126116 discloses a position detection device which detects an indicated position using a pen. The position detection device disclosed in Japanese Unexamined Patent Application Publication No. 2017-126116 has a plurality of loop coils and a voltage detection amplifier. The loop coils are provided for receiving a signal with a frequency transmitted by a pen as a position detection device. The amplifier detects the signal received by the loop coils. The plurality of loop coils are coupled to the voltage detection amplifier through a reception channel selection switch group. The reception channel selection switch group has a plurality of switches respectively corresponding to the loop coils. One ends of the loop coils are coupled to a reference voltage source, while the other ends thereof are coupled to one input terminal of the voltage detection amplifier through respectively corresponding switches. A reference voltage output by the reference voltage source is input to the other input terminal of the voltage detection amplifier.

In the reception channel selection switch group, one of a plurality of switches is controlled to be ON, while the rest of switch(es) is controlled to be OFF. By so doing, one of the plurality of loop coils is coupled to the voltage detection amplifier. The voltage detection amplifier detects and amplifies a reception signal received by the coupled loop coil. In the position detection device, the reception signal received and amplified by the voltage detection amplifier is sampled by a sampling circuit, and input to a signal process arithmetic circuit. The signal process arithmetic circuit performs various arithmetic operations including DFT (Discrete Fourier Transform) for the sampling data of the reception signal, and calculates the amplitude and phase of the reception signal.

Japanese Unexamined Patent Application Publication No. 2003-114243 discloses a battery pack voltage detection circuit. The battery pack voltage detection circuit disclosed in Japanese Unexamined Patent Application Publication No. 2003-114243 has a resistance element circuit formed from a predetermined number of resistance elements, a differential amplifier having a pair of input terminals, and a multiplexer. In the resistance element circuit, one ends of the predetermined number of resistance elements are individually coupled to the electrode terminals of a plurality of battery modules which are coupled in series to form a battery pack. The multiplexer has a plurality of switching elements for individually coupling the other ends of the resistance elements and input ends of the differential amplifier. The multiplexer controls a pair of switching elements to be ON in a sequential order, and outputs a voltage of each battery module sequentially to the differential amplifier.

SUMMARY

In Japanese Unexamined Patent Application Publication No. 2017-126116, if a source voltage variation occurs, this variation is transmitted to one input terminal of the voltage detection amplifier, through a power source of a control circuit (driving circuit) of each switch included in the reception channel selection switch group. At this time, a reference voltage source is coupled to the other input terminal of the voltage detection amplifier. Thus, the voltage of the other input terminal is not effected by the voltage variation. In this case, the voltage of one input terminal is varied. This results in generating an unintentional signal in the output of the voltage detection amplifier. This unintentional signal causes error detection.

In Japanese Unexamined Patent Application Publication No. 2003-114243, a plurality of resistance elements are coupled to both input terminals of the differential amplifier. Because different numbers of resistance elements are coupled to the input terminals of the differential amplifier, when a source voltage variation is transmitted from the control circuit of the switch, an unintentional signal is generated in the output of the differential amplifier.

Japanese Unexamined Patent Application Publication No. 2002-353495 discloses an optical coupling device which can improve a CMRR (Common Mode Rejection Ratio). Japanese Unexamined Patent Application Publication No. 2002-353495 discloses a technique for improving the CMRR by providing a dummy photodiode adjacent to the photodiode, in the optical coupling device to be realized as a photo coupler. Though Japanese Unexamined Patent Application Publication No. 2002-353495 discloses a configuration for improving the CMRR only for one photo diode as a sensor, it does not disclose any configuration for improving the CMRR for a plurality of sensors.

Any other objects and new features will be apparent from the descriptions of this specification and the accompanying drawings.

According to one embodiment, a semiconductor device has a first switch group which selectively outputs a signal input from the first group of sensor coupling terminals and a reference voltage, from an output terminal; a second switch group which selectively outputs a signal input from the second group of sensor coupling terminals and the reference voltage, from an output terminal; a first input terminal which is coupled to the output terminal of the first switch group; a second input terminal which is coupled to the output terminal of the second switch group; and a differential amplifier which amplifies and outputs a differential voltage between two input terminals. The number of switches included in the first switch group is equal to a number of switches included in the second switch group. When to select a sensor included in the first group of sensors, a reference voltage is selected in the second switch group. When to select any one of signals input from the second group of sensor coupling terminals in the second switch group, a reference voltage is selected in the first switch group.

According to the one embodiment, in a semiconductor device to which a plurality of sensors are coupled, even when a power source voltage variation occurs, it is possible to suppress detection of an unintentional signal.

DETAILED DESCRIPTION

Descriptions will now specifically be made to preferred embodiments to which means for solving the above problem is applied, by reference to the accompanying drawings. For easy descriptions, the following descriptions and drawings are appropriately omitted or simplified. Those elements illustrated in the drawings as functional blocks for performing various processes may be configured using a CPU (Central Processing Unit), a memory, or any other circuits, in hardware, while they are realized by a program loaded in the memory in software. It is obvious for the skilled in the art that these functional blocks can be realized in any form by only the hardware, the software, or a combination of them, and thus will not be limited to any of them. In the accompanying drawings, the same constituent elements are identified by the same reference numerals, and will not be described over and over, as needed.

The above-described programs are stored using various types of non-transitory computer readable mediums, and can be supplied to a computer. The non-transitory computer readable mediums include various types of substantial recording mediums. Examples of the non-transitory computer readable mediums include a magnetic recording medium (for example, a flexible disk, a magnetic tape, a hard disk), a magneto-optical recording medium (for example, a magneto-optical disk), a CD-ROM (a Read Only Memory) CD-R, a CD-R/W, and a semiconductor memory (for example, a mask ROM, a PROM (Programmable ROM), an EPROM (Erasable PROM), a flash ROM, a RAM (Random Access Memory)). The program may be supplied to the computer, using any of the various types of non-transitory computer readable mediums. Examples of the non-transitory computer readable mediums include an electrical signal, an optical signal, and an electromagnetic wave. The non-transitory computer readable mediums can supply a program to the computer, through a wired communication path, such as an electric wire and an optical fiber, or a wireless communication path.

In the following preferred embodiments, if necessary for convenience sake, descriptions will be made to divided plural sections or preferred embodiments, however, unless otherwise specified, they are not mutually irrelevant, but one is in relations of modifications, details, supplementary explanations of a part or whole of the other. In the following preferred embodiments, in the case of reference to the number of elements (including the quantity, numeric value, amount, range), unless otherwise specified and unless clearly limited in principle, the present invention is not limited to the specified number, and a number over or below the specified one may be used.

Further, in the following preferred embodiments, the constituent elements (including the operation steps) are not necessarily indispensable, unless otherwise specified and unless considered that they are obviously required in principle. Similarly, in the following preferred embodiments, in the reference of the forms of the constituent elements or the positional relationships, they intend to include those approximating or similar substantially to the forms and like, unless otherwise specified and unless considered that they are obviously not required in principle. This is also true of the foregoing numerals (the quantity, numeric value, amount, range).

First Embodiment

FIG. 1illustrates a semiconductor device according to a first embodiment. A semiconductor device10has a differential amplifier11, an ADC (Analog to Digital Converter)12, a signal process arithmetic unit13, a reference voltage source14, a driving circuit15, a control circuit16, a switch circuit20, and a dummy impedance circuit30. To the semiconductor device10, a 2n-number of sensors50-1to50-2n are coupled, when “n” is an integer equal to or greater than 1. The semiconductor device10is used for detecting the position of a target object to be measured, by receiving an electrical signal which is generated a mutual interaction (electromagnetic induction or electrostatic capacity) between the sensors50-1to50-2n.

The reference voltage source14generates a reference voltage. The reference voltage source14may be of an overall feedback type, in which a reference potential is given to, for example, a positive input terminal. The reference voltage generated by the reference voltage source14is output from an IC (Integrated Circuit) terminal ROUT as a reference voltage output terminal to the sensors50-1to50-2n. The reference voltage generated by the reference voltage source14is also output to the dummy impedance circuit30. The reference voltage source14is not necessarily included in the semiconductor device10, and may be provided outside the semiconductor device10. In this case, a reference voltage may be input to the dummy impedance circuit30through a reference voltage input terminal.

One ends of the sensors50-1to50-2n are coupled to IC terminals SIN1to SIN2n as sensor coupling terminals. The other ends of the sensors50-1to50-2n are gathered in one, and coupled to the reference voltage source14through the IC terminal ROUT. The sensors50-1to50-2n are configured as the same type of sensors. The sensors50-1to50-2n are configured as sensors detecting, for example, a frequency signal. The sensors50-1to50-2n are configured using, for example, loop coils.

The switch circuit20includes a switch group21and a switch group22. The switch group21has an n-number of switches (sensor coupling switches) SW1to SWn corresponding to the n-number of sensors50-1to50-nand a switch (bias voltage switch) SWD+ corresponding to the reference voltage. One ends of the switches SW1to SWn are respectively coupled to the IC terminals SIN1to SINn, the other ends thereof are coupled to one input terminal (positive input terminal) of the differential amplifier11. One end of the switch SWD+ is coupled to the output of the reference voltage source14through the dummy impedance circuit30, and the other end thereof is coupled to the positive input terminal of the differential amplifier11. The switch group21selectively outputs a signal input from50-1to50-nthrough the IC terminal SIN1to SINn and a reference voltage input from the reference voltage source14through the dummy impedance circuit30.

The switch group22has an n-number of switches (sensor coupling switches) SWn+1 to SW2n corresponding to an n-number of sensors50-n+1 to50-2n and a switch (bias voltage switch) SWD− corresponding to a reference voltage. One ends of the switches SWn+1 to SW2n are coupled respectively to IC terminals SINn+1 to SIN2n, while the other ends thereof are coupled to the other input terminal (negative input terminal) of the differential amplifier11. One end of the switch SWD− is coupled to the output of the reference voltage source14through the dummy impedance circuit30, while the other end thereof is coupled to the negative input terminal of the differential amplifier11. The switch group22selectively outputs a signal input from the n-number of sensors50-n+1 to50-2n through the IC terminals SINn+1 to SIN2n and a reference voltage input from the reference voltage source14through the dummy impedance circuit30.FIG. 1illustrates an example in which the switch group21is coupled to the positive input terminal, and the switch group22is coupled to the negative input terminal. However, instead, the switch group21may be coupled to the negative input terminal, and the switch group22may be coupled to the positive input terminal.

As described above, the switch group21has an n+1-number of switches SW1to SWn and SWD+. The switch group22has the n+1-number of switches SWn+1 to SW2n and SWD−. In this embodiment, the switch groups21and22have the same number of switches. Each of the switches SW1to SW2n, SWD+, and SWD− included in the switch groups21and22is configured using, for example, a field effect transistor. The field effect transistors used for the switch groups21and22have the same sizes, for example, in their gate width and the gate length. In other words, the switches SW1to SW2n, SWD+, and SWD− included in the switch groups21and22all are to have the same electric characteristics.

The driving circuit15drives the switches in the switch groups21and22. The driving circuit15includes a logical circuit, for example, an inverter or a buffer, and drives the gate of the field effect transistor configured as each switch. The control circuit (switch control circuit)16controls selection (ON) and non-selection (OFF) of each switch in the switch groups21and22, through the driving circuit15. The control circuit16controls any one of the switch SW1to SW2n to be ON, and controls the rest to be OFF. The control circuit16controls one of the switches SWD+ and SWD− to be ON, and controls the other switch to be OFF. The sensor corresponding to the ON switch of the switches SW1to SW2n represents a sensor to be selected.

The control circuit16controls the switch SWD− to be ON in the switch group22, when turning ON any of the switches SW1to SWn in the switch group21. That is, the control circuit16controls the switch group22to select a reference voltage, when to select any of the signals input from the IC terminals SIN1to SINn in the switch group21. When the control circuit16controls the switch SWD+ to be ON in the switch group21, when turning ON any of the switches SWn+1 to SW2n in the switch group22. That is, the control circuit16controls the switch group21to select a reference voltage, when to select any of the signals input from the IC terminals SINn+1 to SIN2n in the switch group22. The control circuit16sequentially selects the sensors50-1to50-2n, while switching the sensors one by one in a predetermined order. This selection order is arbitrary, and is not particularly restricted.

The differential amplifier11amplifies and outputs a differential voltage between a signal (voltage) output from an output terminal of the switch group21and a signal output from an output terminal of the switch group22. When any of the signals input from the IC terminals SIN1to SINn is selected in the switch group21, the differential amplifier11amplifies a differential voltage between the selected signal and a reference voltage input through the dummy impedance circuit30and the switch SWD−. When any of the signals input from the IC terminals SINn+1 to SIN2n is selected in the switch group22, the differential amplifier11amplifies a differential voltage between the selected signal and a reference voltage input through the dummy impedance circuit30and the switch SWD+.

In this case, the sensors50-1to50-2n are provided between the switches SW1to SW2n and the reference voltage source14, while the dummy impedance circuit30is provided between the switches SWD+ and SWD− and the reference voltage source14. The dummy impedance circuit30is arranged to equalize the impedance between the switches SWD+ and SWD− and the reference voltage source14and the impedance between the switches SW1to SW2n and the reference voltage source14. The impedance value of the dummy impedance circuit30is set to a value which is obtained by adding an impedance component of an interaction between the sensors and a target object to be measured to an impedance value of the sensors, instead of the same impedance value as the impedance value of the sensors themselves. When there is no interaction therebetween, or when there is only a slight effect of the interaction, the impedance value of the dummy impedance circuit30is set to the same value as the impedance value of the sensors themselves.

The impedance value of the dummy impedance circuit30is set to a value which is obtained by adding the impedance component generated due to mutual induction to the impedance value of the sensors. For example, in the position detection device disclosed in Japanese Unexamined Patent Application Publication No. 2017-126116, a loop coil is used in the sensor, and the position detection device performs position detection using electromagnetic induction between the position indication device as a target object to be measured and the loop coil. In this case, mutual induction M occurs between the sensors and the position indication device. When the impedance value of the dummy impedance circuit30is set as a resultant value of adding the mutual induction M to the impedance value of the sensors, it is possible to having uniform impedances between both input terminals of the differential amplifier11(voltage detection amplifier in Japanese Unexamined Patent Application Publication No. 2017-126116), at the time of detecting a reception signal.

When the mutual interaction has the electrostatic capacity, the impedance value of the dummy impedance circuit30is set to a value obtained by adding the capacitance component generated by the mutual capacitance to the impedance value of the sensors. The impedance generated by the mutual interaction is not limited to a positive value, and may be a negative value. The impedance value of the dummy impedance circuit30is set to a desired impedance value in the frequency of the reception signal. The dummy impedance circuit30can be configured using a resistor and a capacitor, as long as it is not effected by a source voltage variation.

An ADC12converts an analog voltage signal output by the differential amplifier11into a digital signal. The ADC12outputs sampling data of the output signal from the differential amplifier11which has been converted into the digital signal to the signal process arithmetic circuit13. The signal process arithmetic unit (signal process circuit)13performs a signal process for the output signal of the differential amplifier11which is input through the ADC12. The signal process arithmetic unit13extracts a predetermined frequency component from the reception signal by performing, for example, discrete Fourier transform for the sampling data of the output signal from the differential amplifier11, to perform various arithmetic operations.

For example, when the switch SW1in the switch group21is selected and turned ON, the positive input terminal of the differential amplifier11is coupled to the sensor50-1through the switch SW1. At this time, the switch SWD− in the switch group22is selected and turned ON, and the negative input terminal of the differential amplifier11is coupled to the reference voltage source14through the switch SWD−. The differential amplifier11amplifies the reception signal received by the sensor50-1by a mutual interaction between the target object to be measured and the sensor50-1. Then, the ADC12samples the reception signal. The signal process arithmetic circuit13performs various arithmetic operations including the discrete Fourier transform for the sampling data obtained by the ADC12, thereby obtaining information including the amplitude or phase of the reception signal of the sensor50-1.

For example, when the switch SWn+1 in the switch group22is selected and turned ON, the negative input terminal of the differential amplifier11is coupled to the sensor50-n+1 through the switch SWn+1. At this time, the switch SWD+ in the switch group21is selected and turned ON, and the positive input terminal of the differential amplifier11is coupled to the reference voltage source14through the switch SWD+. The differential amplifier11amplifies a reception signal received by the sensor50-n+1 by a mutual interaction between the target object to be measured and the sensor50-n+1. The ADC12samples the reception signal. The signal process arithmetic circuit13performs various arithmetic operations including discrete Fourier transform for the sampling data obtained by the ADC12, thereby obtaining information including the amplitude or phase of the reception signal of the sensor50-n+1.

In this embodiment, the switches SW1to SWn are coupled to the positive input terminal of the differential amplifier11, and the switches SWn+1 to SW2n are coupled to the negative input terminal of the differential amplifier11. Thus, when the switches SW1to SWn are selected, or when the switches SWn+1 to SW2n are selected, the polarity of the reception signal output by the differential amplifier11is reversed. Similarly, the polarity of the sampling data of the reception signal obtained by the ADC12is reversed. The signal process arithmetic circuit13performs a reverse process for the sampling data in accordance with the selected switch, thereby enabling to have uniform polarities of the reception signals. The signal process arithmetic circuit13does not perform the reverse process, when any of, for example, the switches SW1to SWn is selected, and performs the reverse process, when any of the switches SWn+1 to SW2n is selected. The relationship between the selected switch and performance/non-performance of the reverse process may be the other way round. In this manner, in a state where the same polarity is made, various arithmetic operations can be performed for the reception signal.

In this embodiment, one of the switches SW1to SW2n is selected for a 2n-number, that is, an even number of sensors51-1to50-2n. Then, the signal of the sensors50-1to50-2n is input to and received by the differential amplifier11. In this embodiment, the switch groups21and22have the same number of switches, and the same number of switches are coupled to the positive input terminal and the negative input terminal of the differential amplifier11. The control circuit16selects a switch to be coupled to the IC terminals SIN1to SINn or SINn+1 to SIN2n in one of the switch groups21and22, and selects one switch to be coupled to the reference voltage source14. That is, of the switches included in the switch groups21and22to be coupled to the positive input terminal and the negative input terminal, one switch is controlled to be ON, and the rest of the switches are controlled to be OFF.

FIG. 2schematically illustrates an equivalent circuit of the semiconductor10in one aspect. The equivalent circuit illustrated inFIG. 2corresponds to a state where the switch SW1in the switch group21is selected, and also the switch SWD− in the switch group22is selected. A resistor RON1illustrated inFIG. 2represents on-resistance of a field effect transistor included in the switch SW1, while a resistor RON2represents on-resistance of a field effect transistor included in the switch SWD−. The positive input terminal of the differential amplifier11is coupled to the reference voltage source14through the resistor RON1, the IC terminal SIN1, the sensor50-1, and the IC terminal ROUT. On the other hand, the negative input terminal of the differential amplifier11is coupled to the reference voltage source14through the resistor RON2and the dummy impedance circuit30.

A capacitor CP1illustrated inFIG. 2represents a parasitic capacitance for a power source VDD of an “n+1-number” of switches SW1to SWn and SWD+ coupled to the positive input terminal of the differential amplifier11. A capacitor CP2represents a parasitic capacitance for a power source VDD of an n+1-number of switches SWn+1 to SW2n and SWD− coupled to the negative input terminal of the differential amplifier11. Capacitors CIN1and CIN2represent input capacitances for the positive input terminal and the negative input terminal of the differential amplifier11and a ground GND. In the switch groups21and22, the resistance value of a non-selective switch is to be assumed as infinity, and a resistance component of the non-selective switch is not illustrated in the equivalent circuit illustrated inFIG. 2.

In this embodiment, the same number of switches are coupled to the positive input terminal and the negative input terminal of the differential amplifier11. Thus, the parasitic capacitance CP1and the parasitic capacitance CP2are equal to each other, and the input capacitance CIN1and the input capacitance CIN2are equal to each other. Further, the resistors RON1and RON2coupled to the positive input terminal and the negative input terminal have the equal resistance value. Note that the impedance at the non-detection by the sensor50-1, that is, the impedance of the sensor50-1itself differs from the impedance of the dummy impedance circuit30. The impedance of the sensor50-1increases or decreases by a value corresponding to a mutual interaction with a target object to be measured, at the detection. The impedance value of the dummy impedance circuit30is set to the impedance at the detection, thereby having uniform impedances at the positive input terminal and the negative input terminal of the differential amplifier11at the detection.

InFIG. 2, let it be considered a case in which a variation occurs in the power source VDD. The variation in the source voltage is transmitted to the positive input terminal and the negative input terminal of the differential amplifier11, through the power source of the driving circuit15of the switches included in the switch groups21and22. In this embodiment, as described above, the positive input terminal and the negative input terminal of the differential amplifier11have the equal impedance. Thus, the same amount of variation is transmitted to the positive input terminal and the negative input terminal of the differential amplifier11. The same effect of the source voltage variation is given to the positive input terminal and the negative input terminal of the differential amplifier11, thereby canceling the effect of the source voltage variation in the output of the differential amplifier11. Thus, any unintended signal (amplitude change) is not generated in the output of the differential amplifier11, thus suppressing detection of the unintended signal.

In this embodiment, the semiconductor device10is coupled to the 2n-number of sensors50-1to50-2n. The switch group21selectively outputs a signal input from the n-number of sensors50-1to50-nand a reference voltage to the positive input terminal of the differential amplifier11. The switch group22selectively outputs a signal input from the n-number of sensors50-n+1 to50-2n and a reference voltage to the negative input terminal of the differential amplifier11. In this embodiment, the switch groups21and22have the same number of switches. The control circuit16selects a reference voltage in the switch group22, when to select any of the sensors50-1to50-nin the switch group21. The control circuit16selects a reference voltage in the switch group21, when to select any of the sensors50-n+1 to50-2n in the switch group22. In this manner, it is possible substantially to equalize the variation transmitted to the positive input terminal and the negative input terminal of the differential amplifier11, when a variation occurs in the source voltage, and also to suppress detection of any unintended signal in the output of the differential amplifier11. Thus, in this embodiment, it is possible to enhance the tolerance (PSRR: Power Supply Rejection Ration) for a source voltage variation, and to detect a minute signal with high accuracy.

In this embodiment, the impedance value of the dummy impedance circuit30is set to a value obtained by adding or subtracting the impedance value by a value corresponding to a mutual interaction between the sensor and the target object to be measured, to or from the impedance value of the sensor itself. In this case, in a state where a mutual interaction occurs between the sensor and the target object to be measured, it is possible to have the uniform impedance values between the positive input terminal of the differential amplifier11and the negative input terminal. Thus, in a state where the sensor reacts with the target object to be measured, it is possible to suppress detection of an intended signal and to enhance detection performance of the sensors.

In this embodiment, the dummy impedance circuit30can be configured using a resistor and a capacitor. In this case, an advantage is that the dummy impedance circuit30is configured inside the semiconductor device10. When the dummy impedance circuit30is configured inside the semiconductor device, unlike Japanese Unexamined Patent Application Publication No. 2002-353495, there is no need to couple a dummy sensor to the semiconductor device10. The semiconductor device10does not need an IC terminal for coupling to the dummy sensor. Thus, in this embodiment, it is possible to minimize the effect to the external part of the semiconductor device10, for example, any external component or any extra IC terminal, and to improve the PSRR characteristics.

Second Embodiment

Descriptions will now be made to a second embodiment.FIG. 3illustrates a semiconductor device according to the second embodiment.

The semiconductor device10aaccording to this embodiment has differential amplifiers11aand11b, ADCs12aand12b, signal process arithmetic circuits13aand13b, a reference voltage source14, a driving circuit15, a control circuit16, switch circuits20aand20b, and dummy impedance circuits30aand30b.

In this embodiment, a “4n-number” of sensors50-1to50-4n are coupled to the semiconductor device10a. The semiconductor device10ahas a configuration with two sets of the semiconductor device according to the first embodiment, as illustrated inFIG. 1. That is, each of the sets includes the differential amplifier11, the ADC12, the signal process arithmetic circuit13, the switch circuit20, and the dummy impedance circuit30. The semiconductor device10amay be configured with three or more sets of the above. The differential amplifier11a, the ADC12a, the signal process arithmetic circuit13a, the reference voltage source14, the driving circuit15, a control circuit16a, the switch circuit20a, the dummy impedance circuit30a, and the sensors50-1to50-2a may be the same as those of the first embodiment.

One ends of the sensors50-2n+1 to50-4n are coupled to IC terminals SIN2n+1 to SIN4n as sensor coupling terminals. The other ends of the sensors50-2n+1 to50-4n are gathered in one, and coupled to the reference voltage source14through the IC terminal ROUT.

The switch circuit20bincludes switch groups21band22b. The switch group21bhas an n-number of switches SW2n+1 to SW3n corresponding to an an-number of sensors50-2n+1 to50-3n and a bias voltage switch SWDb+ corresponding to the reference voltage. One ends of the switches SW2n+1 to SW3are coupled respectively to IC terminals SIN2n+1 to SIN3n, and the other ends thereof are coupled to the one input terminal (positive input terminal) of the differential amplifier11b. One end of the switch SWDb+ is coupled to the output of the reference voltage source14through the dummy impedance circuit30b, and the other end thereof is coupled to the positive input terminal of the differential amplifier11b. The switch group21bselectively outputs a signal input from the sensors50-2n+1 to50-3n through the IC terminals SIN2n+1 to SIN3n and a reference voltage input from the reference voltage source14through the dummy impedance circuit30b.

The switch group22bhas an n-number of switches SW3n+1 to SW4n corresponding to an n-number of sensors50-3n+1 to50-4n and a bias voltage switch SWDb− corresponding to the reference voltage. One ends of the switches SW3n+1 to SW4n are coupled respectively to IC terminals SIN3n+1 to SIN4n, while the other ends thereof are coupled to the other input terminal (negative input terminal) of the differential amplifier11b. One end of the switch SWDb− is coupled to the output of the reference voltage source14through the dummy impedance circuit30b, while the other end thereof is coupled to the negative input terminal of the differential amplifier11b. The switch group22bselectively outputs a signal input from the n-number of sensors50-3n+1 to50-4n through the IC terminals SIN3n+1 to SIN4n and a reference voltage input from the reference voltage source14through the dummy impedance circuit30b.

The driving circuit15drives the switches of the switch groups21band22b, in addition to the switches in the switch groups21aand22a. The control circuit16controls also selection (ON) and non-selection (OFF) of the switches in the switch groups21band22b, through the driving circuit15. The control circuit16controls any one of the switches SW2n+1 to SW4n to be ON, and controls the rest to be OFF. The control circuit16controls one of the switches SWDb+ and SWDb− to be ON, and controls the other one thereof to be OFF.

The differential amplifier11bamplifies a differential voltage between a signal (voltage) output from the output terminal of the switch group21band a signal output from the output terminal of the switch group22b, and outputs it. When any of the signals input from the IC terminals SIN2n+1 to SIN3n in the switch group21bis selected, the differential amplifier11bamplifies a differential voltage between the selected signal and a reference voltage input through the dummy impedance circuit30band the switch SWDb−. When any of the signals input from the IC terminals SIN3n+1 to SIN4n in the switch group22bis selected, the differential amplifier11bamplifies a differential voltage between the selected signal and a reference voltage input through the dummy impedance circuit30band the switch SWDb+.

In this embodiment, the control circuit16selects any one of the sensors50-1to50-2n and any one of the sensors50-2n+1 to50-4n. When the control circuit16controls any of the switches SW1to SWn included in the switch group21ato be ON, it controls a switch SWDa− in the switch group22ato be ON. When the control circuit16controls any of the switches SWn+1 to SW2n included in the switch group22a, it controls a switch SWDa+ in the switch group21ato be ON. When the control circuit16controls any of the switches SW2n+1 to SW3n included in the switch group21bto be ON, it controls a switch SWDb− included in the switch group22b. When the control circuit16controls any of the switches SW3n+1 to SW4n included in the switch group22bto be ON, it controls a switch SWDb+ included in the switch group21bto be ON.

In this embodiment, the semiconductor device10ahas the two differential amplifiers. The differential amplifiers11ais used for detecting a reception signal of the sensors50-1to50-2n, while the differential amplifier11bis used for detecting a reception signal of the sensors50-2n+1 to50-4n. In the first embodiment, when the total number of sensors is sixty, an operation for selecting a sensor and receiving a signal therefrom is repeated sixty times. In this embodiment, on the other hand, it is possible to process parallelly for any of signals of the sensors50-1to50-2n and any of signals of the sensors50-2n+1 to50-4n. Thus, the operation for selecting the sensor and receiving the signal is repeated simply thirty times. In this embodiment, it is possible to attain an effect of improving the detection speed, in addition to an effect of improving the PSRR characteristics attained in the first embodiment.

Third Embodiment

Now, descriptions will be made to a third embodiment.FIG. 4illustrates a semiconductor device according to a fourth embodiment. The semiconductor device10baccording to this embodiment has a control circuit (impedance control circuit)40, a memory41, a voltage signal source42, and a control circuit43, in addition to the configuration of the semiconductor device10according to the first embodiment illustrated inFIG. 1. In this embodiment, the dummy impedance circuit30is configured in a manner that the impedance value is set variable. Any other points are the same as those of the first embodiment.

The dummy impedance circuit30is configured with, for example, a variable resistor. The dummy impedance circuit30is configured with, for example, a FET (transistor), such as an nMOSFET (metal-oxide-semiconductor field-effect transistor), and controls a voltage applied to the gate of the FET which is output from the control circuit40, thereby enabling to realize a desired resistance value. The FET may be a pMOSFET. For example, the voltage to be applied to the gate of the FET which is output from the control circuit40is controlled using a variable voltage regulator without being effected by a source voltage variation. Alternatively, the voltage to be applied to the gate may be controlled, using a DAC (Digital to Analog Converter). When the voltage to be applied to the gate is controlled using some unit like a DAC which is effected by a source voltage variation, it is preferred to provide a filter for decreasing the frequency of a reception signal for the output of the DAC. Because the filter may simply be provided in the control circuit40, it results in a small area impact.

The dummy impedance circuit30may be configured with a variable capacitor. For example, the capacitance value of the gate capacitance of the FET has voltage dependency. Changing the bias voltage value attains a desired capacitance value. The bias voltage is supplied from, for example, a regulator without being effected by a source voltage variation. Alternatively, the bias voltage may be supplied from the DAC. When the bias voltage is controlled using some unit like a DAC which is effected by a source voltage variation, like described above, it is preferred to provide a filter for decreasing the frequency of a reception signal for the output of the DAC.

The control circuit40controls the impedance value of the dummy impedance circuit30. The control circuit40controls, for example, an output voltage of the above-described regulator or a digital value input to the DAC, thereby controlling the impedance value of the dummy impedance circuit30. The control circuit40performs calibration for making the impedance value of the dummy impedance circuit30equal to a desired impedance value. When a sensor is selected from a plurality of sensors, the control circuit40performs calibration for the impedance value of the dummy impedance circuit30. The control circuit40stores control information (control value) for realizing the desired impedance value obtained by the calibration, in the memory41. At the detection of a target object to be measured, the control circuit40controls the impedance value of the dummy impedance circuit30, based on the control information read from the memory41.

In this embodiment, the positive input terminal of the reference voltage source14is coupled to the voltage signal source42, instead of the reference potential. The voltage signal source42is configured to be able to output a signal of a predetermined frequency. The control circuit43controls the voltage signal source42. When the above-described calibration is performed, the control circuit43outputs a signal of a predetermined frequency to the voltage signal source42. In this case, the reference voltage source14outputs a frequency signal with a predetermined amplitude. At the detection of a target object to be measured, the control circuit43controls the voltage signal source42to output a fixed voltage, for example, a half voltage of the source voltage VDD. In this case, the reference voltage source14generates a reference voltage, similarly to the case of the first embodiment.

In this case, the reference voltage source14is coupled to the sensors50-1to50-2n and the dummy impedance circuit30, and coupled also to the positive input terminal and the negative input terminal of the differential amplifier11through a selected switch. For example, in a circuit configuration in which the voltage signal source42is effected by a source voltage variation, a signal with a predetermined amplitude, as output by the reference voltage source14, is effected by the source voltage variation. Even in this case, the positive input terminal and the negative input terminal of the differential amplifier11are equally effected by the source voltage variation, thereby canceling the variation in the output of the differential amplifier. Thus, the voltage signal source42and the reference voltage source14may have a circuit configuration which is effected by the source voltage variation.

FIG. 5illustrates a calibration operation procedure. The control circuit16controls the switches of the switch groups21and22, and selects a target sensor for calibration, through the driving circuit15(Step S1). The control circuit16controls only, for example, the switch SW1in the switch group21to be ON, and controls only the switch SWD− in the switch group22to be ON, thereby selecting the sensor50-1. For example, the user fixes a target object to be measured, in a position away from the selected sensor by a desired distance (Step S2). The target object to be measured is fixed in a position sufficiently away from the sensor by, for example, 10 cm. The control circuit40sets impedance value of the dummy impedance circuit30to the minimum (Step S3).

The control circuit43controls the voltage signal source42to output a signal with the same frequency as that of the reception signal. In this case, the reference voltage source14outputs a signal with a predetermined frequency equal to that of a frequency of the reception signal (Step S4). The signal with the predetermined frequency, as output by the reference voltage source14, is input to the sensor50-1through the IC terminal ROUT. The signal with the predetermined frequency is input to the dummy impedance circuit30. The positive input terminal of the differential amplifier11is coupled to the sensor50-1through the switch SW1, while the negative input terminal thereof is coupled to the dummy impedance circuit30through the switch SWD−. The differential amplifier11amplifies a potential difference between the positive input terminal and the negative input terminal, and outputs it. The ADC12samples the output of the differential amplifier11.

The signal process arithmetic circuit13calculates the amplitude of sampling data output by the ADC12(Step S5). To calculate the amplitude using the output of the ADC12, the ADC12needs to perform the sampling for a period equal to or longer than a half cycle of the reception frequency, based on a sampling theorem. The amplitude is 0 (constant value), when the impedance value of the sensor50-1which includes the mutual interaction is equal to the impedance value of the dummy impedance circuit30.

The signal process arithmetic circuit13judges whether the amplitude calculated in Step S5is 0 (Step S6). When the signal process arithmetic circuit13judges that the amplitude is not 0, the control circuit40increments the impedance value of the dummy impedance circuit30by a predetermined value (Step S7). After this, the process returns to Step S5, and the signal process arithmetic circuit calculates the amplitude. The processes from Step S5to Step S7are repeatedly performed until it is judged that the amplitude is 0 in Step S6.

When it is judged that the amplitude is 0 in Step S6, the control circuit40stores a control value for realizing the impedance value of the dummy impedance circuit30in the memory41, in the case where the amplitude is 0 (Step S8). As described above example, the control circuit40sets the minimum impedance value of the dummy impedance circuit30in Step S3, and the impedance value is incremented gradually thereafter in Step S6. However, it is not limited to this example. For example, the control circuit40may set the maximum impedance value in Step S3, and may gradually decrement the impedance value in Step S6.

The above-described calibration may be performed for a part or entire of the 2n-number of sensors50-1to50-2n coupled to the semiconductor device10b. In this case, the control circuit40may store the sensor selected in Step S1and a control value of the dummy impedance circuit30in the memory41in association with each other. When the sensor is used, the control circuit43controls the voltage signal source42to output a constant voltage, for example, VDD/2. Every time the selected sensor is switched, the control circuit40may read a control value corresponding to a sensor to be newly selected from the memory41, and may control the dummy impedance circuit30based on the read control value.

In the above-described calibration, the impedance value of the dummy impedance circuit30, which has an amplitude of 0, may be obtained under a plurality of conditions of different distances, while changing the distance between the target object to be measured and the selected sensor. For a particular sensor, the calibration may be performed in accordance with the above procedure, in a case where the target object to be measured and the sensor are in contact with each other (distance: 0 cm) or adjacent to each other (for example, distance: 1 cm). Alternatively, when the distance between the target object to be measured and the sensor can be assumed as infinite, that is, when there is no target object to be measured, the same procedure as described above can be performed. In the case, the control circuit40may store the distance and the control value of the dummy impedance circuit30in the memory41in association with each other.

At the time of detection, the distance between the target object to the measured and the sensor has a correlation with the amount of the mutual interaction. For example, when the mutual interaction is electromagnetic induction, mutual induction M is large as the distance is short. Thus, the distance between the target object to be measured and the sensor is indicated in the amplitude of the reception signal. The control circuit40may acquire the amplitude value calculated at the detection, of the sampling data obtained by the ADC12, from the signal process arithmetic circuit13. Then, the circuit40may read a control value corresponding to the distance estimated based on the amplitude value from the memory41, and may control the dummy impedance circuit30based on the read control value.

In this case, one of the switches SWD+ and SWD− is controlled to be ON, while the other one thereof is controlled to be OFF. For example, when the switch SWD− is controlled to be ON, the switch SWD+ is controlled to be OFF. At this time, let it be assumed that the control circuit40controls both of the dummy impedance circuits coupled to the switches SWD+ and SWD−, based on the read control value read from the memory41. In this case, because the switch SWD+ is controlled to be OFF, no effect is produced on the reception signal, regardless of the impedance value of the dummy impedance circuits30. Thus, the control circuit40does not need to be configured to control individually the two dummy impedance circuits30.

The sensors50-1to50-2n may include different types of sensors, or may include sensors of different reception frequencies. In this case, the frequency of a frequency signal output from the reference voltage source14in Step S4may be changed in accordance with the sensor selected in Step S1. By setting the frequency of the signal output by the voltage signal source42coupled to the reference voltage source14at the reception frequency of each sensor, the impedance value of the dummy impedance circuit30can be matched with the impedance of the sensor at the detection, even when different types of sensors are used.

[Variable Range of Impedance Value]

Descriptions will now be made to a variable range of the impedance value of the dummy impedance circuit30. Descriptions will be made to a case in which the semiconductor device10baccording to this embodiment is used for the same position detection device as Japanese Unexamined Patent Application Publication No. 2017-126116.FIG. 6schematically illustrates an example of the sensor and the position indication device. The sensors50-1to50-2n are configured as loop coils. The loop coil group including the sensors50-1to50-2n is arranged in a monitor of a PC (Personal Computer) having the paper size of, for example, A4. One ends of the sensors50-1to50-2n are coupled respectively to the IC terminals SIN1to SIN2n, while the other ends thereof are coupled to the IC terminals ROUT. The self-inductance of each loop coil is L1(positive real number).

A position indication device60has a frequency signal generation unit61, a capacitor62, and a coil63. Self-inductance of the coil63is L2(positive real number). The position indicating device60is configured as a pen-type device, and has a size of a general writing tool. In this case, the relationship between the self-inductance L1of the sensors50-1to50-2n and the self-inductance L2of the coil63in the position indicating device60is L1>L2, based on the relationship between the size of the position indicating device and the screen size.

In general, the mutual inductance M is expressed by M=k(L1*L2)1/2, where k is a coupling coefficient having a value greater than −1 and smaller than 1. Thus, the condition of the mutual inductance M is −(L1*L2)1/2<M<(L1*L2)1/2. Because L1>L2, (L1*L2)1/2<L1is satisfied.

In this case, the dummy impedance circuit30is preferred to simply change the impedance value in a range of the impedance corresponding to L1±(L1*L2)1/2, in the frequency of the reception signal. When this dummy impedance circuit is used, the impedance value can be adjusted to an impedance value for realizing the amplitude 0 at the time of calibration, for any distances. When the winding direction (polarity) of the loop coil and the coil63of the position indicating device60is set in advance, it is possible to limit the variable range to a positive range (impedance range corresponding from 0 to (L1*L2)1/2) or a negative range (impedance range corresponding from −(L1*L2)1/2to 0). The dummy impedance circuit30is not necessarily configured with an inductor.

FIG. 7schematically illustrates another example of a sensor and a position indication device. The sensors50-1to50-2n are configured as loop coils. In this example, the sensors50-1to50-nare configured in a loop coil group50-X on the X axis, while the sensors50-n+1 to50-2n are configured in a loop coil group50-Y on the Y axis.FIG. 7illustrates the loop coil group50-X and the loop coil group50-Y in a manner that they are separated from each other, and they are in fact attached to each other and arranged in an overlapped state. Note, however, that the loop coil group50-X and the loop coil group50-Y are electrically independent from each other.

One ends of the loop coils of the loop coil group50-X are coupled respectively to the IC terminals SIN1to SINn, while the other ends thereof are coupled to the IC terminal ROUT. One ends of the loop coils of the loop coil group50-Y are coupled respectively to the IC terminals SINn+1 to SIN2n, while the other ends thereof are coupled to the IC terminal ROUT. The self-inductance of each loop coil of the loop coil group50-X is L1X (positive real number), while the self-inductance of each loop coil of the loop coil group50-Y is L1Y (positive real number). PC monitors generally have different lengths in a vertical side (Y axis) and a horizontal side (X axis). When the size of the screen in the horizontal direction is greater than the size of the vertical side, the relationship between the self-inductance L1X of the loop coil group50-X and the self-inductance L1Y of the loop coil group50-Y is L1Y<L1X. Like this example, the sensors50-1to50-2n may include two types of sensors whose self-inductance differs from each other.

When the loop coils (sensors50-n+1 to50-2n) of the loop coil group50-Y are selected in the semiconductor device10b, the switch SWD+ is controlled to be ON. The variable range of the impedance value requested for the dummy impedance circuit30coupled to the switch SWD+ is L1Y±(L1Y*L2)1/2, while the variable range of the impedance value requested by the dummy impedance circuit30coupled to the switch SWD− is L1X±(L1X*L2)1/2. That is, it is required that the variable width of the dummy impedance circuit30coupled to the switch SWD− is greater than the variable width of the dummy impedance circuit30coupled to the switch SWD+. In this case, the variable width of both of the dummy impedance circuits30may be ±(L1X*L2)1/2. The variable range may be L1Y±(L1X+L2)1/2for the dummy impedance circuit30coupled to the switch SWD+, and may be L1X±(L1X+L2)1/2for the dummy impedance30coupled to the switch SWD−.

When the self-inductance L2of the coil63included in the position indication device60is unknown, the relationship of the self-inductance is L2<L1Y<L1X. Thus, the variable range of the dummy impedance circuit30coupled to the switch SWD+ may be L1Y±L1Y. In addition, the variable range of the dummy impedance circuit30coupled to the switch SWD− may be L1X±(L1X*L1Y)1/2. In this case, the value of the self-inductance L2can correspond to various different position indication devices60.

In the described above example, the loop coils of the loop coil group50-X are coupled to the IC terminals SIN1to SINn, and the loop coils of the loop coil group50-Y are coupled to the IC terminals SINn+1 to SIN2n. However, it is not limited that the entire loop coils of the loop coil group50-X are coupled to the IC terminals SIN1to SINn, and the entire loop coils of the loop coil group50-Y are coupled to the IC terminals SINn+1 to SIN2n. It may be unknown that the coils of which loop coil group are coupled to the IC terminals SIN1to SIN2n. In this case, the variable range of the dummy impedance circuits30coupled to the switches SWD+ and SWD− may preferably be a range from the minimum value to the maximum value of the variable range of the two dummy impedance circuits30coupled to the respective switches SWD+ and SWD−. Specifically, based on the relationship L2<L1Y<L1X, the variable range of both of the dummy impedance circuits30coupled to the switches SWD+ and SWD− may preferably be a range from 0 to L1X+(L1X*L1Y)1/2. When the self-inductance L2of the coil63is known, and when it is unknown that the coils of which loop coil group are coupled to the IC terminals SIN1to SIN2n, the variable range of both of the dummy impedance circuits30coupled to the switches SWD+ and SWD− may preferably be a range from L1Y−(L1Y*L2)1/2to L1X+(L1X*L2)1/2.

In this embodiment, the impedance value of the dummy impedance circuit30is configured to be variable. The control circuit40performs calibration, and stores a control value for controlling the impedance value of the dummy impedance circuit30to coincide with the impedance value of the sensor with which a mutual interaction occurs, in the memory41. At the time of detection, the control circuit40reads the control value stored at the time of calibration from the memory41, to control the impedance value of the dummy impedance circuit30based on the control value. As a result, the impedance value of the dummy impedance circuit30can coincide accurately with the impedance value of the sensor at the detection, thereby improving the PSRR characteristics at the detection.

In this embodiment, the above-described calibration can be performed for the entire sensors50-1to50-2n. In this case, even if a manufacturing irregularity is generated in the sensors50-1to50-2n or the dummy impedance circuit30, it is possible to optimize the impedance value of the dummy impedance circuit30. The above-described calibration can be performed for the distance of a plurality of target objects to be measured. In this case, at the detection, it is possible to optimize the impedance for various distances, by controlling the impedance value of the dummy impedance circuit30in accordance with the distance between the sensor and the target object to be measured.

First Modification

In the above-described embodiments, the descriptions have been made to the case wherein an even number of sensors are coupled to the semiconductor device10. However, the semiconductor device10may have a configuration with an odd number of IC terminals coupled to the sensors and an odd number of sensors coupled thereto.FIG. 8illustrates a semiconductor device according to a first modification. The configuration of a semiconductor device10caccording to this modification is the same as the configuration of the semiconductor device10illustrated inFIG. 1, except that the IC terminal SIN2n is excluded therefrom. In this embodiment, the switch SW2n included in the switch group22is not coupled to the IC terminal, and is open. Any other points may be the same as any of the above embodiment.

One end of the switch SW2n is open, while the other end thereof is coupled to the negative input terminal of the differential amplifier11. The one end of the switch SW2n may be coupled to wiring to which a constant voltage is supplied from the power source VDD or ground GND. The control circuit16controls any of the 2n−1-number of switches SW1to SW2n−1 to be ON, and controls the rest to be OFF. The control circuit16controls the switch SW2n to be always OFF. When any of the switches SW1to SWn in the switch group21is selected, the control circuit16selects the switch SWD− in the switch group22. When any of the switches SWn+1 to SW2n−1 in the switch group22, the control circuit16selects the switch SWD+ in the switch group21. As a result, like the first embodiment, it is possible to detect the reception signal of the selected sensor.

FIG. 8illustrates an example in which the switch group22includes a switch which is not coupled to the sensor coupling IC terminal. The position of the switch not coupled to the IC terminal is arbitrary. For example, the switch group21may include a switch not coupled to the IC terminal. More particularly, for example, when the switch group21has an n-number of switches SW1to SWn, and also the switch group22has an n-number of switches SWn+1 to SW2n, one end of the switch SW1may be open without being coupled to the IC terminal. Even in this case, unless the switch SW1is controlled to be ON, the same operation as described above can be realized.

The descriptions have been made to the example wherein the semiconductor device10cdoes not have the IC terminal SIN2n. However, in this modification, the semiconductor device10cmay have the IC terminal SIN2n, like the semiconductor device10according to the first embodiment. In this case, no sensor is coupled to any one of the 2n-number of switches SW1to SW2n. It is not limited that the number of IC terminals to which no sensor is coupled is one. No sensor may be coupled to an arbitrary number of IC terminals. The control circuit16controls the switch coupled to the IC terminal to which no sensor is coupled, to be OFF. For example, when no sensor is coupled to the IC terminal SIN2n, the control circuit16always controls the switch SW2n to be OFF. Also in this case, the same operation as described above can be realized.

Second Modification

In the above-described embodiments, the descriptions have been made to the example wherein the signal process arithmetic circuit13performs a process for reversing the polarity. However, it is not limited to this.FIG. 9illustrates a part of a semiconductor device according to a second embodiment. In this modification, the differential amplifier11is configured as a differential amplifier which is of a double differential output type. In this modification, the ADC12is configured as an ADC of a double differential input type. Switches SWX1to SWX4are polarity reversing switches for reversing the polarity of a signal to be input to the ADC12.

For example, when any of the switches SW1to SWn in the switch group21is selected, the switches SWX2and SWX3are controlled to be ON, and the switches SWX1and SWX4are controlled to be OFF. In this case, positives are coupled with each other, and negatives are coupled with each other, in the output of the differential amplifier11and the input of the ADC12. In the switch group22, when any of the switches SWn+1 to SW2n in the switch group22is selected, the switches SWX1and SWX4are controlled to be ON, and the switches SWX2and SWX3are controlled to be OFF. In this case, the positive of the output of the differential amplifier11and the negative of the input of the ADC12are coupled with each other, and the negative of the output of the differential amplifier11and the positive of the input of the ADC12are coupled with each other. In this modification, the signal process arithmetic circuit13performs various arithmetic operations, including discrete Fourier transform, for sampling data, without performing the arithmetic operation for reversing the polarity.

In this modification, each two of the switches SWX1to SWX4are controlled to be selected, and the values of the impedance (parasitic capacitance) are made equal to each other, for both positive and negative inputs of the ADC12. Though the switches SWX1to SWX4may possibly be effected by a source voltage variation, the effect of the source voltage variation is canceled, because the effect is produced on both of the positive and negative inputs of the ADC12. Thus, it is possible to realize reversing of the signal polarity without deteriorating the PSRR characteristics. In this modification, the signal process arithmetic circuit13does not need to perform an arithmetic operation for reversing the polarity, thus enabling to reduce the arithmetic time. The reversing operation of the polarity as described in this modification is applicable to the second and third embodiments, or the first and third modifications.

Third Modification

In the above-described embodiments, the dummy impedance circuits30are arranged individually for the switches SWD+ and the switch SWD−. However it is not limited to this example.FIG. 10illustrates a semiconductor device according to a third modification. A semiconductor device10daccording to this modification differs from the semiconductor device10according to the first embodiment illustrated inFIG. 1in that the dummy impedance circuit30is arranged commonly for the switches SWD+ and the switch SWD−. Any other points may be the same as those of the second or third embodiment, or any other points may be the same as those of the first or second modification. In this modification, an advantage is that one impedance circuit30can be excluded.

In the first embodiment, each the dummy impedance circuits30is coupled to one switch. In this embodiment, on the other hand, the dummy impedance circuit30common to both switches is coupled to the positive input terminal and the negative input terminal of the differential amplifier11through the switches SWD+ and SWD−. Thus, the best impedance value of the dummy impedance circuit30is one which has been obtained by subtracting the impedance value of one switch (SWD+ or SWD−) controlled to be OFF from the value explained in the first embodiment.

In general, because the switch needs to pass the reception signal, it has only a small parasitic component which does not produce an effect on a signal in the frequency of the reception signal. On the other hand, because the sensor has high sensitivity (for example, a resonance frequency) for the frequency of the reception signal, it has the impedance sufficiently higher than the parasitic component of the one switch controlled to be OFF. Thus, in principle, the impedance value can be optimized by subtracting the impedance value of one switch. However, in fact, it can be considered that any serious problem will not occur, even when the impedance value of the dummy impedance circuit30is set at the same value as that described in the first embodiment or its approximation value.

Another Modification

Any of the above-described embodiments and modifications can arbitrarily be combined together.FIG. 11illustrates a semiconductor device according to another modification in combination of the second embodiment and the third modification. Like a semiconductor device10aaccording to the second embodiment illustrated inFIG. 3, a semiconductor device10ehas the differential amplifiers11aand11b, the ADC12aand12b, the signal process arithmetic circuits13aand13b, the reference voltage source14, the driving circuit15, the control circuit16, the switch circuits20aand20b, and the dummy impedance circuits30aand30b. The semiconductor device10eis configured with two sets of the differential amplifier, the ADC, the signal process arithmetic circuit, the switch circuit, and the dummy impedance circuit. The semiconductor device10emay be configured with three or more sets of the above.

In the modification illustrated inFIG. 11, like the third modification, the dummy impedance circuits30aand30bare arranged commonly to two bias voltage switches. The dummy impedance circuit30ais coupled to the positive input terminal of the differential amplifier11athrough the switch SWDa+, and coupled to the negative input terminal of the differential amplifier11athrough the switch SWDa−. The dummy impedance circuit30bis coupled to the positive input terminal of the differential amplifier11bthrough the switch SWDb+, and coupled to the negative input terminal of the differential amplifier11bthrough the switch SWDb−. The impedance values of the dummy impedance circuits30aand30bmay be the same as those described in the third modification. When this semiconductor device10eis used, it is possible to attain the effect attained in the second embodiment and the effect attained in the third modification.

FIG. 12illustrates a semiconductor device according to still another modification in combination of the third embodiment and the third modification. A semiconductor device10fhas the same configuration as that of the semiconductor device10baccording to the third embodiment illustrated inFIG. 4. In the semiconductor device10f, like the third modification, the dummy impedance circuit30whose impedance value is variable is arranged commonly to two bias voltage switches SWD+ and SWD−. The calibration of the impedance value of the dummy impedance circuit30may be the same as that described in the third embodiment. When this semiconductor device10eis used, it is possible to attain the effect of the third embodiment and the effect of the third modification. Like the semiconductor device10aaccording to the second embodiment, the semiconductor device10emay be configured with two sets of the differential amplifiers, the ADC, the signal process arithmetic circuit, the switch circuit, and the dummy impedance circuit.

FIG. 13illustrates a semiconductor according to still yet further modification. A semiconductor device10ghas IC terminals SIND+ and SIND− for coupling to the dummy sensors. To the IC terminals SIND+ and SIND−, one ends of dummy sensors50-D are coupled. The dummy sensors50-D have the same configuration as any other sensors. The dummy sensors50-D are shielded, and do not react to a target object to be measured. The other ends of the dummy sensors50-D are coupled to the reference voltage source14through the IC terminal ROUT. In the semiconductor10g, the dummy impedance circuits30are coupled to the dummy sensors50-D through the IC terminals SIND+ and SIND−. Any other points are the same as those of the semiconductor device10according to the first embodiment illustrated inFIG. 1.

In the first embodiment, the impedance value of the dummy impedance circuit30is set to a value which is obtained by adding an impedance value of a mutual interaction between the sensor and the target object to be measured, to the impedance value of the sensor. In the semiconductor device10g, the impedance value of the dummy impedance circuit30is set to an impedance value corresponding to impedance generated by mutual induction, when the mutual interaction is, for example, electromagnetic induction. When the mutual interaction is, for example, electrostatic capacity, the impedance value of the dummy impedance circuit30is set to an impedance value corresponding to capacitance generated by mutual capacitance. InFIG. 13, the dummy impedance circuit30is arranged inside the semiconductor device10g. However, the dummy impedance circuit30may be arranged outside the semiconductor device10g.

The semiconductor device10ghas the IC terminals SIND+ and SIND− to which the dummy sensors50-D are coupled. It is possible to couple an arbitrary dummy sensor50-D to the IC terminals SIND+ and SIND−. This enables to correspond to the impedance of the sensor which has not been assumed in designing of the semiconductor device. The dummy sensors50-D may have a configuration in which the impedance value is variable, like the third embodiment. In this case, by performing the calibration, it is possible accurately set the same impedance between both input terminals of the differential amplifier11.

Accordingly, the present invention by the present inventors have specifically been described based on the preferred embodiments. The present invention is not limited to the preferred embodiments. Various changes may possibly be made without departing from the scope thereof.

For example, a part or the entire of the above embodiments may also be described as the following additional notes, but is not limited thereto.

A semiconductor device comprising:

a first group of sensor coupling terminals to which a first group of sensors are coupled;

a second group of sensor coupling terminals to which a second group of sensors are coupled;

a first switch group which selectively outputs a signal input from the first group of sensor coupling terminals and a reference voltage, from an output terminal;

a second switch group which selectively outputs a signal input from the second group of sensor coupling terminals and the reference voltage, from an output terminal;

a switch control circuit which controls the first switch group and the second switch group to select one sensor included in the first group of sensors or the second group of sensors;

a differential amplifier which has a first input terminal coupled to the output terminal of the first switch group and a second input terminal coupled to the output terminal of the second switch group, and amplifies and outputs a differential voltage between the first input terminal and the second input terminal; and

a signal process circuit which performs a signal process for an output signal of the differential amplifier,

wherein a number of switches included in the first switch group is equal to a number of switches included in the second switch group, and

wherein, when to select a sensor included in the first group of sensors, the switch control circuit controls to select any of signals input from the first group of sensor coupling terminals in the first switch group and to select the reference voltage in the second switch group, and when to select a sensor included in the second group of sensors, the switch control circuit controls to select any of signals input from the second group of sensor coupling terminals in the second switch group and to select the reference voltage in the first switch group.

The semiconductor device according to additional note 1,

wherein the first switch group includes at least one sensor coupling switch one end of which is coupled to the first group of sensor coupling terminals and other end thereof is coupled to the first input terminal, and a first bias voltage switch one end of which is coupled to the reference voltage and other end thereof is coupled to the first input terminal,

wherein the second switch group includes at least one sensor coupling switch one end of which is coupled to the second group of sensor coupling terminals and other end thereof is coupled the second input terminal, and a second bias voltage switch one end of which is coupled to the reference voltage and other end thereof is coupled to the second input terminal.

The semiconductor device according to additional note 2,

wherein the first group of sensor coupling terminals and the second group of sensor coupling terminals include dummy sensor coupling terminals coupled to dummy sensors and supplied with the reference voltage,

wherein one ends of the first bias voltage switch and the second bias voltage switch are coupled to the reference voltage respectively through the dummy sensor coupling terminals and the dummy sensors.

The semiconductor device according to additional note 2, further comprising

a dummy impedance circuit between the first bias voltage switch and the reference voltage and also between the second bias voltage switch and the reference voltage.

The semiconductor device according to additional note 4,

wherein an impedance value of the dummy impedance circuit is set based on an impedance value of the first group of sensors and the second group of sensors and a variation of impedance which is generated by a mutual interaction between the sensors and a target object to be measured.

The semiconductor device according to additional note 4 or 5,

wherein the dummy impedance circuit is arranged individually between the first bias voltage switch and the reference voltage and also between the second bias voltage switch and the reference voltage.

The semiconductor device according to additional note 4 or 5,

wherein the dummy impedance circuit is arranged commonly between the first bias voltage switch and the reference voltage and between the second bias voltage switch and the reference voltage.

The semiconductor device according to additional note 3, further comprising

a dummy impedance circuit between one ends of the first bias voltage switch and the second bias voltage switch, and the dummy sensor coupling terminal.

The semiconductor device according to additional note 8,

wherein an impedance value of the dummy impedance circuit is set based on a variation of impedance which is generated by generating a mutual interaction between sensors used in the first group of sensors and the second group of sensors and a target object to be measured.

The semiconductor device according to any one of additional notes 4 to 9,

wherein the dummy impedance circuit has a configuration in which an impedance value is variable.

The semiconductor device according to additional note 10,

wherein a target object to be measured and the sensors include inductance, and a mutual interaction between the sensors and the target object to be measured is electromagnetic induction, and wherein, when L1represents a positive real number representing self-inductance of the sensors and L2represents a positive real number representing self-inductance of the target object to be measured, the dummy impedance circuit has a configuration in which an impedance value is variable in a range from an impedance value corresponding to L1−(L1*L2)1/2to an impedance value corresponding to L1+(L1*L2)1/2.

The semiconductor device according to additional note 11,

wherein the dummy impedance circuit has a configuration in which an impedance value is variable in a range from an impedance value corresponding to L1−(L1*L2)1/2to an impedance value corresponding to L1, or in a range from the impedance value corresponding to L1to an impedance value corresponding to L1+(L1*L2)1/2.

The semiconductor device according to additional note 10,

wherein a target object to be measured and the sensors include inductance, a mutual interaction generated between the sensors and the target object to be measured is electromagnetic induction, and the first group of sensors and the second group of sensors include two sensors whose self-inductance differs from each other, and

wherein, when L1X and L1Y represent a positive real number representing self-inductance of the two sensor, when L2represents a positive real number representing self-inductance of the target object to be measured, and when L1Y<L1X is satisfied, the dummy impedance circuit has a configuration in which an impedance value is variable in a range from impedance corresponding to L1Y−(L1Y*L2)1/2impedance corresponding to L1X+(L1X*L2)1/2.

The semiconductor device according to additional note 10,

wherein a target object to be and the sensors include inductance, a mutual interaction generated between the sensors and the target object to be measured is electromagnetic induction, and the first group of sensors and the second group of sensors include two sensors whose self-inductance differs from each other, and

wherein, when L1X and L1Y represent positive real numbers representing self-inductance of the two sensors, when L2represents a positive real number representing self-inductance of the target object to be measured, and when L2<L1Y<L1X is satisfied, the dummy impedance circuit has a configuration in which an impedance value is variable in a range from 0 to impedance corresponding to L1X+(L1X*L1Y)1/2.

The semiconductor device according to additional note 6,

wherein the dummy impedance circuit has a configuration in which an impedance value is variable, a target object to be measured and the sensors include inductance, and a mutual interaction generated between the sensors and the target object to be measured is electromagnetic induction,

wherein, when L1X represents a positive real number representing self-inductance of sensors included in the first group of sensors, when L1Y represents a positive real number representing self-inductance of sensors included in the second group of sensors, and when L2represents a positive real number representing self-inductance of the target object to be measured,the dummy impedance circuit arranged between the first bias voltage switch and the reference voltage has a configuration in which an impedance value is variable in a range from impedance corresponding from L1Y−(L1Y*L2)1/2to L1Y+(L1Y*L2)1/2, andthe dummy impedance circuit arranged between the second bias voltage switch and the reference voltage has a configuration in which an impedance value is variable in a range from impedance corresponding from L1X−(L1X*L2)1/2to L1X+(L1X*L2)1/2.
[Additional Note 16]

The semiconductor device according to additional note 6,

wherein the dummy impedance circuit has a configuration in which an impedance value is variable, a target object to be measured and the sensors include inductance, and a mutual interaction generated between the sensors and the target object to be measured is electromagnetic induction,

wherein, when L1X represents a positive real number representing self-inductance of sensors included in the first group of sensors, when L1Y represents a positive real number representing self-inductance of sensors included in the second group of sensors, when L2represents a positive real number representing self-inductance of the target object to be measured, and when L2<L1Y<L1X is satisfied,the dummy impedance circuit arranged between the first bias voltage switch and the reference voltage has a configuration in which an impedance value is variable in a range from 0 to impedance corresponding to 2*L1Y, andthe dummy impedance circuit arranged between the second bias voltage switch and the reference voltage has a configuration in which an impedance value is variable in a range of impedance corresponding from L1X−(L1X*L1Y)1/2to L1X+(L1X*L1Y)1/2.
[Additional Note 17]

The semiconductor device according to any one of additional notes 10 to 16, further comprising

an impedance control circuit which controls an impedance value of the dummy impedance circuit.

The semiconductor device according to additional note 17,

wherein, in a state where the switch control circuit selects the sensor, the impedance control circuit calibrates an impedance value of the dummy impedance circuit in a manner that an amplitude of an output signal of the differential amplifier is a constant value, and stores control information of the dummy impedance circuit which has been obtained by the calibration in a memory.

The semiconductor device according to additional note 18,

wherein the impedance control circuit stores, when the calibration is performed, information regarding the sensor selected by the switch control circuit and the control information in association with each other, in the memory.

The semiconductor device according to additional note 19,

wherein the impedance control circuit performs the calibration for the sensors included in the first group of sensors and the sensors included in the second group of sensors.

The semiconductor device according to additional note 20,

wherein the impedance control circuit reads the control information corresponding the sensor selected by the switch control circuit from the memory at a time of detecting a target object to be measured, and controls an impedance value of the dummy impedance circuit based on the read control information.

The semiconductor device according to any one of additional notes 18 to 21,

wherein the calibration is performed in a state where a mutual interaction is generated between at least one of the first group of sensors and the second group of sensors and a target object to be measured.

The semiconductor device according to additional note 22,

wherein the impedance control circuit performs the calibration under a plurality of conditions of different distances between the sensor and the target object to be measured, and stores the conditions and the control information in association with each other, in the memory.

The semiconductor device according to additional note 23,

wherein the impedance control circuit reads control information corresponding to the distances between the sensor selected by the switch control circuit and the target object to be measured from the memory, and controls an impedance value of the dummy impedance circuit based on the read control information.

The semiconductor device according to additional note 24,

wherein the impedance control circuit estimates the distance based on an amplitude of an output of the differential amplifier.

The semiconductor device according to any one of additional notes 1 to 25,

a polarity reversing switch which reverses polarity of an output of the differential amplifier between the output of the differential amplifier and the signal process circuit.

The semiconductor device according to any one of additional notes 1 to 26,

wherein at least one of the first switch group and the second switch group includes a non-coupling switch which is not coupled to the first group of sensor coupling terminals or the second group of sensor coupling terminals.

The semiconductor device according to additional note 27,

wherein the switch control circuit does not select the non-coupling switch.

The semiconductor device according to any one of additional notes 1 to 28, further comprising

two or more sets of the first group of sensor coupling terminals, the second group of sensor coupling terminals, the first switch group, the second switch group, the differential amplifier, and the signal process circuit.

The semiconductor device according to any one of additional notes 1 to 29, further comprising

a reference voltage source for generating the reference voltage.

The semiconductor device according to additional note 30, further comprising

a reference voltage output terminal for outputting the reference voltage, and

wherein one ends of the first group of sensors and the second group of sensors are coupled to the reference voltage output terminal.

The semiconductor device according to any one of additional notes 1 to 31,

wherein electric characteristics of the switches included in the first switch group are same as electric characteristics of the switches included in the second switch group.