JPS6134632B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electronic wristwatch that is less susceptible to the effects of external magnetic fields.More specifically, the present invention relates to an electronic wristwatch that is less susceptible to the effects of external magnetic fields. The aim is to provide electronic watches that are less susceptible to influences. The motors used in electronic wristwatches are easily affected by external magnetic fields; for example, the motor malfunctions when exposed to a DC magnetic field of 30 oersted and an alternating current magnetic field of 5 oersted. Although this electronic wristwatch uses a shield plate to reduce the influence of external magnetic fields, it is particularly weak against alternating current magnetic fields compared to direct current magnetic fields. Items that generate alternating magnetic fields include electric razors, alternating current motor transformers, etc. Even during daily use of wristwatches, the motors are sometimes affected, so countermeasures have been urgently needed. However, to solve the above problem, electronic wristwatches using, for example, magnetoresistive elements, Hall element reed switches, etc., have been devised to detect external magnetic fields. There were problems such as low magnetic field detection sensitivity, large power loss for detection, and the need for additional space for these elements. For this reason, it is impossible to detect a magnetic field of several oersteds with an electronic wristwatch that has a limited energy source and limited space, and until now, electronic wristwatches with magnetic field detection elements have not been put into practical use. Ta. The present invention eliminates these drawbacks and detects an external magnetic field, especially an alternating current magnetic field, without using a special detection element and with almost negligible power consumption, and controls the drive current of the motor to detect the alternating magnetic field. The present invention provides an electronic wristwatch that is less susceptible to the effects of Next, the principle of the alternating current magnetic field detection method used in the electronic wristwatch of the present invention will be explained, but before that, the configuration of the most suitable motor to which the detection principle of the present invention is applied will be explained. 1 is a coil wound around a magnetic core made of a high magnetic permeability material, 2 is a stator made of a high magnetic permeability material, and 3 is a rotor made of a permanent magnet material magnetized into two poles in the radial direction. As shown in FIG. 2, a pulse is applied to this motor in which the direction of the current applied to the coil 1 is reversed every time, thereby causing the rotor 3 to rotate in a fixed direction. The present invention is characterized in that the coil 1 of the motor is used as an alternating current magnetic field detection element without using a special magnetic field detection element. If the motor is exposed to an alternating magnetic field,
The voltage induced in the coil 1 will be explained. FIG. 3 schematically depicts the coils and magnetic core 4 of the motor. Since the coils used in motors usually have an elongated shape, the external magnetic field tends to concentrate on the magnetic core 4 of the coil, and depending on the shape, the magnetic flux density can be about 10 times higher, although it cannot be said that this is true. is normal. The voltage υ induced in the coil 1 at this time is given by υ=-n·dΦ/dt, where n is the number of turns of the coil and Φ is the magnetic flux of the magnetic core 4.

[Table] When using a magnetic core with the shape shown in Table 1,
Assuming that the magnetic flux density inside the magnetic core is 10 times that outside, the magnetic flux Φ of the magnetic core 4 is given by the following equation. Φ
=10×S×B×sinwt... Here, S is the cross-sectional area of the magnetic core 4, and B (Gauss) is the peak value of the magnetic flux density of the alternating magnetic field. , from the formula, υ=−10×
n x S x B x W x coswt = -10 x 1 x 10 ⁴ (turn) x 0.6 x 10 ^-4 (m ² ) x B x 10 ^-4 (Wb/m ² ) x 2
π×50(Hz)×coswt=−6.4π× ^10-2 ×B×
coswt [V] = -0.20 x Bcoswt [V], therefore, if B of the magnetic flux density of the external magnetic field is 2 Gauss, υ = -0.4 coswt [V]. If the motor is used in something like a wristwatch where space for an energy source is limited, then 0.4 [V]
Since it is not possible to operate the control circuit with a detection voltage of about 100 MHz, it is necessary to amplify the voltage enough to control the C-MOS inverter. However, the current situation is such that it is difficult to create a C-MOS amplifier that operates stably, and the greatest feature of the AC magnetic field detection device used in the electronic wristwatch of the present invention is that The purpose is to detect an alternating current magnetic field of about 1 oersted without any problem. In addition, here we considered the state when the magnetic core 4 exists alone in the magnetic field, but in reality, the magnetic core 4 is arranged as a part of the motor component, so the bypass effect by the stator causes the magnetic core 4 to The magnetic flux that gathers in is reduced compared to the case alone. Since the induced voltage in the coil 1 becomes correspondingly smaller, the method used in the electronic wristwatch of the present invention becomes more effective in detecting a magnetic field on the order of 1 oersted. A feature of the alternating current magnetic field detection device for an electronic wristwatch of the present invention is that by alternately connecting low impedance elements and high impedance elements, such as low resistance and high resistance elements, to both ends of the motor coil, voltage induced in the coil by an external magnetic field is detected. , the presence of an external magnetic field can be easily detected by amplifying it without using a special amplifier. FIG. 4 shows an external magnetic field detection circuit consisting of a motor drive circuit 200, an amplifier section 201, and a detection section 202. Generally, all elements except the motor coil 20 are built in a CMOSIC. Here, the principle of amplification will be explained in detail, and the configuration and operation of the circuit will be explained later. In Fig. 4, 21 and 22 are P-type MOSFET gates (hereinafter abbreviated as P gate), 23, 24, 2
5 and 26 are N-type MOSFET gates (hereinafter abbreviated as N gates), detection resistors 28 and 29, and motor coil 2.
0, the drive circuit and amplifier section are configured. The method of amplifying the detection signal is when the motor is not driven.
The closed loop of the motor coil 20, N gates 23, 24 and the closed loop of the motor coil 20, detection resistor 29, N gates 26, 23 are alternately switched. The voltage induced in the coil by the external magnetic field is first short-circuited in the closed loop of N gates 23 and 24. These N gates 23 and 24 are transistors for driving the motor, and their ON resistance is generally several 10
Since the voltage generated in the coil is short-circuited by this ON resistance, a relatively large current flows. Next, the motor coil 20, the N gate 26, 2
3. When the closed loop of the detection resistor 29 is switched, since the motor coil 20 has an inductance component, there is an effect that continues to flow the relatively large current that was flowing before switching, and the detection resistor 29 is momentarily generates a large voltage,
Thereafter, the voltage reaches a steady state determined by the detection resistor 29, the induced voltage due to the external magnetic field, the coil resistance, etc., and becomes stable. In this steady state, the voltage when the detection resistor is increased to infinity is the voltage when the above-mentioned switching is not performed. Next, in this method, the magnification factor for amplifying the induced voltage due to the external magnetic field is determined. A in FIG. 5 is an N gate, and B in FIG. 5 is its equivalent circuit. The switch 40 is turned on and off by a gate signal. 39 is ON when driving
The resistor and diode 41 are PN junction diode between the substrate and the drain, and the capacitor 42 is the PN junction capacitance between the substrate and the drain, the drain gate capacitance, and
This is the sum of pad capacitance, stray capacitance, etc. If this equivalent circuit is replaced with the P gate and N gate of FIG. 4, and the battery is a large capacity capacitor and an ideal power source, the equivalent circuit of this detection method will be as shown in FIG. 6. 43 is the voltage V ₀ generated by the external magnetic field, 44
is the coil that makes up the motor, and the inductance is L Henry, 45 is the internal resistance of the coil, rΩ, and 47
is the loop changeover switch, and 46 is the N gate ON
Resistance rNΩ, but here we ignore this rNΩ because it is sufficiently smaller than the coil resistance value. 48
is the parasitic capacitance of the N gate and P gate, and is the sum of the parasitic capacitance of the N gate 24 and the P gate 22, which is C
It's Huarad. 49 is a detection resistor, RsΩ, 50 and 52 are parasitic diodes between the N gate and P gate substrate and drain, 51 is a silver battery for watches, which is generally known as a drive battery, and V _D = 1.57V. The output voltage of the terminal 53 becomes the detection voltage V _RS and is input to the voltage detection element. The response when the changeover switch 47 is switched can be theoretically determined based on the equivalent circuit shown in FIG. a=1/2(r/L+1/CRs), b=r+Rs/
LCRs E=Rs/Rs+rV ₀ , w=√｜ ² −｜ ) When a ² > b, VRs=E[1-{1/w(a-DL/rb)sinhwt+coshwt}e ^-at ] ) When a ² = b, VRs=E{1-(1+at -DL/rbt)e ^-at } ) When a ² < b VRs=E[11/w(a-DL/rb)sinwt+coswt
} e ^-at ] However, t ₀ is the connection time of the low resistance loop, and t is the time. The VRs waveform of the above equation is as shown in FIG. 7A. Next, when this VRs is actually calculated based on an example, L=11 Henry, C=75PF, Rs=150KΩ,
Under the conditions of r = 2.8KΩ, V ₀ = 0.1V, t ₀ = ∞, the time to reach the peak voltage of VRs is approximately 30μ
sec, the peak voltage at this time is 4.2V, and the magnification is approximately 42 times, indicating that the detection signal can be easily amplified without using an analog signal amplifier. However, this logical value assumes that the voltage generated in the coil is constant, but in reality, in the case of a closed loop with high resistance, the time constant of the closed loop is small and the time to reach a steady voltage is relatively quick. When switching to a closed loop with low resistance, the time constant is large and it takes a long time for the voltage to reach a steady state. To explain based on the above example, in the case of a closed loop with high resistance, VRs becomes a nearly steady voltage in about 0.2 msec, but in the case of a low resistance loop, the time constant is τ = L / r. As a result, τ = 3.9 msec, and even if the low resistance loop continues for 3.9 msec, the voltage will be only 63% of the steady voltage. However, the frequency of the AC magnetic field that is most commonly encountered is the commercial power frequency of 50Hz or 60Hz, and its period is 20msec or 16.7msec.In order to detect this maximum strength magnetic field, the pulse width of 3.9msec is long. Too much. B in FIG. 7 is a diagram of the detected voltage when the high resistance loop time is 0.5 msec and the low resistance loop time is 1.5 msec based on the above-mentioned conditions for an AC magnetic field of 50 Hz. In this case, the detection signal amplification factor is approximately 15 times. C in FIG. 7 is a diagram showing this situation, and 5
The straight line 5 is the voltage generated in the coil without switching, and the line 56 is the amplification factor of about 5 when the low resistance loop is switched for 0.5 msec and the high resistance loop is switched for 0.5 msec. Further, the straight line 57 shows the case where switching is performed with a high resistance loop of 0.5 msec and a low resistance loop of 1.5 msec. In this way, the high-resistance loop and low-resistance loop switching time cannot be taken very long to detect AC magnetic fields at commercial frequencies. It can be seen that the time for the low resistance loop should be longer than the time for . As explained above, the detection signal can be amplified simply by switching the circuit including the coil, and the voltage level relative to the reference voltage can be determined without using an analog amplifier, etc., which is difficult to create in a C-MOSIC for watches. By doing so, alternating current magnetic fields can be detected. Furthermore, since the amplification factor can be increased by a factor of 10 or more, it becomes possible to make a judgment based on the threshold voltage of the C-MOS inverter, which is advantageous in terms of power consumption of the entire circuit, circuit configuration, and IC area. Although this embodiment has been described using a resistor as an impedance element for detection, similar detection is possible using a capacitance component or an inductance component. In addition, in this example, all the detection elements are C-
Since it is built into a MOSIC, the low resistance element utilizes the characteristics of the unsaturated part of an active element called a buffer transistor. There is no problem in using active elements in this way. However, when actually configuring the present invention, as in the embodiment used in the present invention, the low resistance loop is the ON resistance of the buffer transistor, and the high resistance loop is the ON resistance of the IC.
It is thought that the diffused resistor and voltage detection element inside are generally C-MOS inverters or comparators. Further, in the description of the present invention, a high resistance is connected in the case of a high resistance loop, but this high resistance may have an infinitely large value, that is, an open loop. Even in this case, there is parasitic capacitance in the buffer transistor,
Because of this capacity component, the amplification is not infinitely large, and detection similar to this explanation is possible. In this case, the advantage is that the timing structure of the circuit becomes simple. Next, a method for making the electronic wristwatch of the present invention difficult to stop when it enters an alternating current magnetic field will be described. FIG. 8 is a graph showing the relationship between the drive pulse width of the motor and AC magnetic resistance. Normally, the motor is driven in the region indicated by 58 in order to increase its efficiency. However, as the pulse width increases, the rotor's circuit position and the timing at which the drive pulse ends interfere with each other, causing malfunctions, and the AC magnetic resistance deteriorates. If the drive pulse width is further increased, it enters the region 59 in FIG. In the region 59, the drive pulse is cut after the rotor is sufficiently attracted by the magnetic flux of the coil, so it is strong against the influence of external magnetic fields. In other words, if it is detected that the watch is exposed to an alternating current magnetic field using the method described above, the motor drive pulse should be the pulse with the best alternating current magnetic resistance in the region of 58, regardless of efficiency. By setting the forced drive pulse in the width or in the region 59 where the pulse width is sufficiently long, it can be used as a motor that is strong against external magnetic fields. Conventionally, in order to aim for maximum efficiency, motors without magnetic field detection circuits sacrifice some magnetic resistance when setting drive pulses, and increase magnetic resistance by adding input parts such as magnetic shield plates and magnetic shield inner frames. However, the method of the present invention is characterized in that it can be used with the pulse width that gives the motor its highest efficiency and with the magnetic resistance that is the highest performance that the motor originally has. Next, one embodiment of the present invention will be described in detail with reference to the drawings. FIG. 4 shows a step motor drive circuit and an external magnetic field detection circuit used in the electronic wristwatch of the present invention. Note that the external magnetic field detection in the embodiments of the present invention is as follows:
This will be explained as an AC magnetic field circuit. P gates 21, 22 and N gates 23, 24 are 2
A pair of CMOS inverters are constructed, and their output terminals a and b are connected to both ends of the coil 20 of the step motor and at the same time to one ends of the detection resistors 28 and 29. The other ends of the detection resistors 28 and 29 are N
It is connected to the source inputs of gates 25 and 26. The positive input terminals of the voltage comparators 30 and 31 are connected to the detection resistor 2.
8 and 29, the negative input terminal is connected to the voltage dividing point of the reference voltage resistor 34, and the output terminals are both connected to the OR gate 32. One end of the reference voltage resistor 34 is grounded via the N gate 27. and gate 3
The two input terminals of 3 are the output of OR gate 32 and N
It is connected to the gate terminal of gate 27. P and N
Gates 21, 22, 23, 24, 25, 26, 2
7 gate terminals 101, 102, 103, 10
4, 105, 106, 107 and and gate 3
The output terminal 110 of No. 3 is connected to the control circuit 65. As shown in the circuit block diagram of FIG. 9, a control circuit 65 appropriately synthesizes frequency-divided signals obtained from a reference signal generating means 66 that generates a reference signal using a crystal oscillator or the like as a source oscillator, and outputs a signal to the drive circuit and the detection circuit. Outputs signals necessary for circuit operation. Various configurations of the control circuit can be considered, one example of which is shown in A and B in Figure 10.
Shown below. In FIG. 10, A is a circuit diagram, and B is a timing chart of input signals. These signals have a period of 1 second and can be easily synthesized from the output of the oscillation frequency divider circuit, so the circuit diagram of that part is omitted. The reset input R of the SR flip-flop (hereinafter abbreviated as SRFF) 70 is connected to the input terminal 110.
The set input S is connected to the signal 121, the output Q, is connected to the input terminals of the AND gates 71 and 72, and the other input terminals of the AND gates 71 and 72 are connected to the signals 123 and 122.
Both output terminals are connected to the input terminal of the OR gate 73. D-type flip-flop (hereinafter referred to as DFF)
(abbreviated as ) 74's clock input CL is connected to the output terminal of OR gate 73, and the positive output Q is connected to AND gate 7.
5 and 76, the negative output is connected to the input terminals of AND gates 77 and 78, and to its own data input terminal D. Other input terminals of AND gates 75 and 77 are connected to the output of OR gate 73, and other input terminals of AND gates 76 and 78 are connected to signal 124. The output of the AND gate 75 is the inverter 7
9 to the output terminal 101, the output of 76 to the output terminal 105, the output of 77 to the output terminal 102 via the inverter 80, the output of 78 to the output terminal 1
Connected to 06. Further, input terminals of OR gates 81 and 82 are connected to the outputs of AND gates 75 and 76, 77 and 78, respectively, and outputs are connected to output terminals 103 and 104 via inverters 83 and 84, respectively. Now, the operation of this embodiment will be explained in detail using timing charts A and B in FIG. 11 and A and B in FIGS. 4 and 10. At A in FIG. 10, SRFF70 is connected to signal 12.
4 every second, the output Q remains in the state of "H" and "L" unless a detection signal appears on the signal 110 as will be explained later. Therefore, the output of the OR gate 73 contains the signal 123.
appears. The DFF74 inverts its output state every time one pulse is input to the clock input CL, and as a result, the signal terminals 101 and 102, 103 and 104, 1
Waveforms 05 and 106 are outputted alternately every second. This waveform is 10 of A in Figure 11.
1, 102, 103, 104, 105, and 106. The signal 123 is a drive pulse for the step motor during normal operation, and its pulse width is determined from the load of the step motor, the volume given, etc. In this embodiment, it is 5.8 msec. The signal 122 is a forced drive pulse that is generated in place of the normal drive pulse when it is detected that the step motor has entered the magnetic field by the action of the AC magnetic field detection circuit according to the present invention. The pulse width should be the one that provides the best AC magnetic resistance depending on the characteristics of the step motor. Generally, the pulse width of the forced drive pulse is longer than the normal pulse width, but in this example, it is 7.8 msec.
It is. Signal 124 is a detection pulse for performing alternating current magnetic field detection according to the present invention. The entire detection interval is
Among the commercial frequencies 50 Hz and 60 Hz, which are considered to be most frequently encountered in daily life, it is sufficient if one wavelength of 50 Hz, which has the longest wavelength, is 20 msec or more. Also intermittent
The duty ratio frequency can be selected with flexibility, but in this example, the frequency was 512 Hz and the duty ratio was 1:3.
(However, it is exaggerated in the figure.) In addition, the signal 107 of A in FIG. It is a signal for masking so that the detection pulse 124 is not generated, and the frequency is the same as the detection pulse 124, and the duty ratio is preferably smaller than the detection pulse 124, and in this embodiment, it is 1:7. In the period before the timing of detecting A in FIG. 11, the P gates 21 and 22 in FIG.
OFF, the N gates 25, 26, and 27 are OFF, both ends of the coil 20 are grounded, the AND gate 33 is masked, and the detection signal 110 is "L". Next, at the timing when the detection pulse rises, the N gates 24, 25, 26, and 27 are turned on, making it possible to perform the intermittent switching of the closed loop including the coil 20 as described in the explanation of the principle. If the step motor is not within the alternating current magnetic field at this time, both ends a and b of the coil are always at 0V and do not reach the detection threshold level _VTH , and the detection signal 110 remains at "L". Therefore, at the timing of the next drive, a normal drive pulse 68 of 5.8 msec is applied. At this timing, only the P gate 22 and the N gate 23 are ON, and current flows through the coil 20 in the direction from b to a. In the next step about 1 second later, the phase is changed and exactly the same operation is performed. Next, B in FIG. 11 shows the case where the step motor enters an alternating current magnetic field. At this time, at the timing of detection, a signal as shown in B in FIG. 11 appears at both ends a and b of the coil, as described in the explanation of the principle. This signal is input to voltage comparators 30 and 31 and compared with a reference voltage V _TH , and if it exceeds V _TH a detection signal 69 is generated. This detection signal 69 is the 10th
It is input to the reset terminal of SRFF 70 in A in the figure to invert its output state. Then, at the timing when the drive pulse immediately after that is output, forced drive pulse 7
0 is applied to the step motor, and it can be driven stably even in an alternating current magnetic field. This concludes the explanation of the operation of the embodiment. As described above, by using the output of the AC magnetic field detection device of the present invention, it is possible to control the motor drive pulse width, control the motor drive voltage, or use the output to generate an alarm to notify the presence of an AC magnetic field. It has become easier to control the buzzer drive circuit. FIG. 12 is an assembled plan view of an embodiment of an electronic wristwatch using the magnetic field detection device of the present invention. As described above, this electronic wristwatch is configured to widen the driving pulse of the motor when a magnetic field is detected. 150 is a motor coil, 151 is a crystal oscillator unit, 152 is a battery accommodating section, 153 is a circuit block in which an oscillation circuit, a frequency dividing circuit, a control circuit, a detection circuit, and a motor drive circuit are housed in one chip IC.
Reference numeral 154 is a trimmer capacitor for adjusting the accuracy of the wristwatch, 155 is an external capacitor, and 156 is a receiver for the train wheel including the rotor. Although the electronic wristwatch using the magnetic field detection device of the present invention has a highly sensitive alternating current magnetic field detection function, the biggest drawback is that it is made of exactly the same components as conventional electronic wristwatches. It has characteristics. The external magnetic field detection device of the present invention is optimal when used in an electronic wristwatch, and can provide a highly sensitive external magnetic field detection device without requiring any new elements in addition to conventional wristwatch components. Not only is the voltage induced in the motor coil
No detection power is required for detection, and the detection circuit also consumes almost no power. Therefore, it is possible to provide an electronic wristwatch equipped with an external magnetic field detection device that is comparable in power consumption and space cost to conventional wristwatches, and its industrial effects are enormous. Further, in the embodiment of the present invention, a motor having the structure shown in FIG. 1 is used, but the motor has a coil,
It goes without saying that the present invention can be applied to a motor having a structure in which a voltage is induced in the coil by an external magnetic field. An electronic wristwatch using the magnetic field detection device of the present invention is
Since the motor drive pulse width is widened only when an external magnetic field is detected, a pulse width with good anti-magnetic characteristics as shown in FIG. 8 can be selected. Therefore, it is possible to provide an electronic wristwatch that uses extremely low power and has excellent AC magnetic resistance. Furthermore, the electronic wristwatch using the magnetic field detection device of the present invention has the characteristic that there is almost no factor for increasing costs, as it does not use any new elements to detect external magnetic fields and only has a circuit devised. . In addition, since the circuit configuration of the detection circuit can be easily realized using C-MOSIC, which is commonly used today, it is possible to realize an electronic wristwatch that is small, thin, low power, low cost, and has excellent AC magnetic resistance, and its industrial effects. There is something tremendous about it.

[Brief explanation of the drawing]

Figure 1 is a diagram showing a watch motor, Figure 2 is a waveform diagram showing inverted pulses, Figure 3 is a diagram showing the state of the coil and magnetic flux in a magnetic field, and Figure 4 is a circuit diagram of the drive circuit and detection circuit. , Figure 5 A is the N channel.
Diagram showing FET gate, Figure 5B is N channel
Fig. 6 is an equivalent circuit diagram of the FET gate, Fig. 6 is an equivalent circuit diagram of the detection circuit, Fig. 7A is a waveform diagram showing the detected voltage waveform, Fig. 7B is a waveform diagram showing the detected voltage waveform in an alternating magnetic field, Fig. 7 Figure C is a diagram showing the relationship between magnetic field strength and detected voltage, Figure 8 is a diagram showing the relationship between drive pulse width and AC magnetic resistance, Figure 9 is a block diagram of the control circuit of the present invention, and Figure 10 A is the control circuit. A circuit diagram showing an example of a circuit configuration, FIG. 10B is a waveform diagram showing an input signal, and FIG.
Figures A and 11B are time charts, and Figure 12 is an assembled plan view of an electronic wristwatch using the magnetic field detection device of the present invention. 1...Coil, 2...Stator, 3...Rotor, 20
...Motor, 21, 22...D gate, 23, 24,
25, 26... N gate, 28, 29... Impedance element, 30, 31... Comparator, 65... Control circuit, 68... Normal drive pulse, 70... Forced drive pulse, 124... Detection pulse, 200... Drive circuit, 201... Amplification Section, 202...Detection section.

Claims (1)

[Scope of Claims] 1. A reference signal generating means for generating a reference signal, a control circuit for outputting a plurality of signals including a step motor drive signal based on an output signal from the reference signal generating means, and at least a stator, a rotor, and a coil. and a drive circuit that inputs a step motor drive signal from the control circuit to drive the step motor, the step motor having a coil with a low impedance element and a high impedance element. an external magnetic field detection circuit consisting of an amplifying section that alternately connects the two, and a detecting section that determines the presence or absence of an external magnetic field based on the voltage value generated in the impedance element of the amplifying section based on the voltage induced in the coil by the external magnetic field. A magnetic field detection device for an electronic watch, characterized in that: 2. The magnetic field detection device for an electronic watch according to claim 1, wherein the amplification section connects the impedance elements alternately for at least 20 msec.