JPS6237726A - Coordinate detector - Google Patents

Abstract

PURPOSE:To detect the coordinates with high stability and high accuracy by impressing the DC bias voltage to an integration filter of a frequency negative feedback system for measurement of the capacity corresponding to the touch position coordinates and preventing the effect caused by the voltage fluctuation of the oscillation frequency. CONSTITUTION:The oscillation output of a voltage control oscillation circuit 24 undergoes a shift of phase by the change of the capacity ratio corresponding to the touch position coordinates given from a capacity terminal 17. Then the voltage corresponding to the measured value obtained via a phase shifter 25, a multiplier 26, an LPF 27, an integrator 29, etc. is negatively fed back to the circuit 24. The oscillation output frequency of the circuit 24 is controlled to a fixed level via a comparator 32. Then, the pulse oscillation output 18 is produced from the comparator 32 in response to the coordinate value. The DC bias voltage proportional to the square of the DC power supply voltage VC supplied to the circuit 24 is impressed to an integrator 28 of this frequency feedback circuit for measurement through a multiplier 26a. Then, the output of the comparator 32 is not dependent on the voltage VC. As a result, the oscillation frequency is set at a fixed level and receives no effect caused by the fluctuation of the power supply voltage. This attains the detection of coordinates with stability and high accuracy.

Description

[Detailed Description of the Invention] [Summary] In a capacitance detection oscillator using a frequency negative feedback system,
By superimposing a bias voltage on the comparator output, it is possible to set the fundamental oscillation frequency, and it is possible to set the appropriate frequency regardless of stray capacitance.

[Industrial application field]

The present invention relates to a coordinate detection device, and more specifically, it is possible to set the oscillation frequency of a capacitance measurement oscillator using a simple method in order to minimize the influence of display noise, and furthermore, the oscillation frequency of the capacitance measurement oscillator can be set in a simple manner. The present invention relates to a device that is stable against changes in power supply voltage and enables highly accurate coordinate detection.

[Conventional technology]

The applicant originally developed a coordinate detection device using a frequency negative feedback system, which consists of a voltage controlled oscillator (41) and a phase shift circuit (42) to which the output signal is input, as shown in FIG.
, a phase comparator circuit (43) that detects the phase difference between the input and output signals of the phase shift circuit, a low pass filter (44) to which the output signal thereof is input, and an output signal of the low pass filter (44). (45) into which the integrator circuit output voltage is input to the voltage controlled oscillator (41).
-''- A frequency negative feedback system in which the phase shift circuit (42) is configured by a first-order all-pass filter (42) consisting of a known resistance R and an unknown capacitance C, and the voltage controlled oscillator (41) This is a capacitance detection device that determines the unknown capacitance C by calculating T/(2πR) from the oscillation period T and the resistance R.

[Problem that the invention seeks to solve]

The capacitance measuring oscillator using the frequency negative feedback system described above has Ih determined by the known resistance R and unknown capacitance C of the phase shift circuit.
= 1/RC, the capacitance change is known from the change in frequency, and the finger touch coordinates are detected. The key to this method is to set the fundamental frequency in the gap (noise window) in the noise spectrum. Generally, on a CRT, the horizontal periodic signal is 15.75kHz and its harmonics, and the commercial frequency is 50/60Hz or the vertical periodic signal is 60Hz. , the frequency needs to be set near 15.75KHz/3. Here, the capacitance lc is, for example, the capacitance of a touch panel, which is composed of the input/output capacitance of an analog switch and stray capacitance, but since its value varies greatly depending on the type of panel (300 to 700 pF), the additional capacitance is determined depending on the type. You need to add it or change the resistance value.

However, the method of adding additional capacitance is the change in capacitance upon touch (
The ratio of human body capacitance (50 to 150 pF) decreases, which is disadvantageous in terms of accuracy.As for the method of adding a resistor, there is a practical upper limit to the resistance value (approximately 40 KΩ), and as it increases, the noise level increases. This is not an appropriate method as it will actually lead to a decrease in accuracy.

For example, if Ω C = 6009F for R-40, then fp "6.6KH, and if the upper limit of touch capacitance is 200 pF, f
Since the touch frequency is -5 KHz, the above R and C values are a guideline for the RC constant when used on a general CRT.

Further, in the conventional method described above, as shown in equation (11), the phase comparator output Acosφ (φ: phase) and the bias voltage ν
The feedback system is configured to oscillate at a frequency such that the sum of e is 05, but since the comparator output is compared to the square of the power supply voltage, when the power supply voltage changes, the output I There is a problem that the frequency changes and causes coordinate errors.

Acosφ + νB ”' O,,, (1) However, φ: Phase angle by phase shift circuit A: Comparator output voltage < VC2 ■8: Bias voltage oc Vc VC: Power supply voltage The present invention is based on the above points. The purpose is to provide a highly accurate coordinate detection device in which the oscillation frequency of the capacitance measurement oscillator is stable against changes in power supply voltage.

[Means for solving problems]

FIG. 1 is a diagram showing the principle of an embodiment of the present invention, FIG. 2 is a configuration diagram of an embodiment of the invention, and FIGS. 3 and 4 are detailed configuration diagrams of an embodiment of the invention.

In the present invention, a voltage controlled oscillator, a phase shift circuit to which the output signal thereof is input, a phase comparison circuit to detect the phase difference between the input and output signals of the phase shift circuit, and an integral filter to which the output signal is input. Consists of a bandpass filter circuit,
The frequency negative feedback system is such that the output is fed back to the voltage controlled oscillator, and the phase shift circuit is constituted by a first-order all-pass filter consisting of a known resistance R and an unknown capacity 1c, and the oscillation period T of the voltage controlled oscillator is In a capacitance detection circuit that knows the unknown capacitance C or the amount of change thereof, there is a coordinate detection device that is equipped with means for adding a DC bias voltage to the output of the phase comparator circuit or the input of the integral filter, thereby making it possible to vary the fundamental frequency of the voltage controlled oscillator. provided, the device is used as a human body capacitance detection device or a capacitive coordinate detection device, and further includes a voltage of a C voltage source commonly applied to the oscillation system as a DC bias voltage. The device can also be used as a human body capacitance detection device or as a capacitive coordinate detection device.

[Function] The above device changes (increases) the CR oscillator constant, which causes a decrease in accuracy. Conventional 9
By making it possible to use a wide range of values without limiting it to 0°,
The oscillation frequency is changed without changing the CR. When there is a phase difference φ, the multiplication result of both is V/2・
The AC component is removed from (cosφ−cos (2ωt+φ)) by a low-pass filter (LPF).
The integrated amount of sφ (DC component) is the voltage controlled oscillator (νC
cos ψ−〇, that is, φ−90°
Stable oscillation (Lock in a phase locked loop (circle, L)) is performed. The present invention uses -
Add bias voltage Shiro instead of cosφ -L cosφ
→ Lock is applied at a phase difference φ such that −v8=0. φ when this is locked is φ−
cos-'(2v8/v)≠90゛.

For example, a first-order all-pass filter (first
), the phase delay φ is φ−2jan−′ ((
I.J. CR).

If ωCR=1, φ-90', ,,,, (21, so it is locked at ω° where ω' CR≠1, and the signal is emitted one time.

ω'cR=A(νB)=const, ,,
,,(31, CR linearity is maintained as T=2π/ω, so there is no effect on the finger touch detection function.

The present invention also provides that the oscillation frequency is defined by the above equation (1),
In particular, pay attention to the fact that the comparator output is proportional to the square of the power supply voltage, and the bias voltage is proportional to the 7h power supply voltage. By doing so, the dependence on the power supply voltage (of the oscillation frequency) is eliminated.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

A first embodiment of the present invention is shown in FIGS. 2 and 3.

The difference from the conventional device is that the output obtained by squaring the power supply voltage νC in a multiplier is used as the bias voltage νB.

In FIG. 2, reference numeral 11 is a coordinate detection device developed by the present applicant, which is a touch panel 12 having transparent electrodes made of ITO, as shown in the diagram of the touch panel 12 consisting of 101 and 14 analog switch arrays, respectively. Analog switches 13a and 13b arranged on the left and right, upper and lower sides include an analog switch 13c for the coordinate detection device 11, and the coordinate detection device 11 is connected to a capacitance measuring section 15 via a buffer amplifier 14, 15 includes a frequency negative feedback type capacitance detection circuit 16, the circuit 16 is connected to the buffer amplifier 14 through a capacitance terminal 17, and the pulse output of the circuit 16 is supplied to an AND gate 20 which receives a 6Mtlz clock signal from the clock 19; The AND gate is connected to the counter 21, and the counter 21 is connected to the micro processing unit (MP[I) 2 for calculations.
2, and an output 23 is output from the MPU 22.

FIG. 3 is a circuit diagram showing details of the frequency negative feedback type capacitance detection circuit 16 shown in FIG. 2. In FIGS. ), 26 is a multiplier, 27 is a low pass filter (LPF), 28 is an integrator, 29 is an inverting circuit, and the resistor 30 (Rδ) connected to the power supply voltage (Vc) is the key point of the present invention. In addition, the linear vCO is part name IC.
The chip is L 8038, and the multiplier is TCL 80.
13 chips are available. Capacitor terminal 1
7 is connected to the touch panel 12 and the human body capacity is measured.
The pulse oscillation output 23 is 2πCR, from which the capacitance value can be determined.

The oscillation frequency is voltage controlled oscillator output −αVc sinωT ,,,(
4) α: constant, Vc: power supply voltage phase comparator output = β・'A (αVc7 cos φ,
,, (51=γ1νc2cosφ, , , , (
61 bias voltage - ν0 β: constant, γ2: constant r Vc2cosφ+V, = 0, ,,,, (
71φ-'l tan-1(ωcR) C, R: In the APF constant, C is the frequency f(2πf-ω) which is an unknown volume.

Here, VB, = 71 Vc2. ,,,, f81
T1: If a constant characteristic can be given, the oscillation frequency ω can be made independent of V.

In FIG. 3, for this purpose, 3/4νC squared by a multiplier is used as VB, and the dependence of the oscillation frequency on the power supply voltage can be eliminated.

(7+, from formula (8), γvC2CO3φ+γ1vC2=0 cos　φ=-γ1/r determines the oscillation frequency and is unrelated to νC.

FIG. 4 shows a second embodiment of the present invention. A bias is supplied to the virtual installation point 31 of the integrator 28 from the power supply Vc through the resistor. By making R8 a variable resistor, the oscillation frequency can be changed. The output of the integrator 28 (νo
ut) is shot-r/CRJ, (?;Vt+v=), u,
,,(Since it is 91, Vin =--LVc 1., (
Io) When 8/l, Vout becomes constant and the oscillation frequency becomes stable.

Here, Vin is the output of the comparator 32, and Vin-νp
cos(2tan-'(ωCR)) ,,
(11) vp: Comparator output peak value. Therefore, it has become possible to set the oscillation frequency by making Rβ or Vc variable.

〔Effect of the invention〕

As described above, according to the present invention, frequency setting is facilitated, and 4) it is effective in suppressing deterioration in accuracy and increasing the reliability of measurement.

[Brief explanation of drawings]

Figure 1 is a diagram showing the principle of an embodiment of the present invention, Figure 2 is a configuration diagram of an embodiment of the invention, Figures 3 and 4 are detailed configuration diagrams of an embodiment of the invention, and Figure 5 is a diagram showing the principle of a conventional device. FIG. In FIGS. 1 to 4, 11 is a coordinate detection device, 12 is a touch panel, 13a, 13b, and 13c are analog switches, and 14
is a buffer amplifier, 15 is a capacitance measurement section, 16 is a frequency negative feedback type capacitance detection circuit, 17 is a capacitance terminal, 18 is a pulse output, 19 is a clock, 20 is an AND gate, 21 is a counter, 22 is an MPU, 23 is an output , 24 is linear vCO1 25 is 8PF. 26 is a multiplier, 27 is an LPF, 28 is an integrator, 29 is a comparator, 30 is a resistor (Rβ), and 31 is a virtual ground point.・Mi1 ′2′・.

Claims (4)

[Claims] (1) Place a resistive film on the panel, measure the capacitance from both ends of the resistive film to the finger touch position on the panel, and use CR to measure impedance to detect the coordinates of the finger touch position from the ratio of these capacitances. In the device (11) using a relaxation oscillator, the output of the phase comparator circuit (18) or the integral filter (28)
) A coordinate detection device which is provided with means (30) for applying a DC bias voltage to the input of the voltage controlled oscillator (24), thereby making it possible to change the fundamental frequency of the voltage controlled oscillator (24). (2) The device according to claim 1, characterized in that the DC bias voltage is a voltage compared to the square of the voltage of a DC voltage source commonly applied to the DC bias voltage oscillator (24). . (3) The device according to claim 1 or 2, which is used to measure human body capacity. (4) The device according to claim 1 or 2, which is used to measure capacitance.