Step motor driving circuit

#This invention is directed to a step motor driving circuit, and in particular to a step motor driving circuit particularly suited for use in an electronic wristwatch that is capable of driving the clock hands of a wristwatch in a forward direction and in a reverse direction.

#In view of the limited space provided in electronic wristwatches for the electronic movement and the battery, it is imperative that the electronic movement consume as little power as possible during operation, in order to prevent a battery from being readily dissipated over long periods of use. Accordingly, efforts are continually made to effect a further reduction in the size of the components of the electronic wristwatch and, at the same time, increase the efficiency of the components. Step motors, utilized in an electronic wristwatch for effecting an incremental driving of the gear train, in response to the electronic timekeeping signals produced by the electronic circuitry, are optimally constructed to obtain greater efficiency and reduced power consumption during operation.

#Moreover, because normal timekeeping operations require that the clock hands be advanced in only a clockwise direction, in order to provide an accurate timekeeping function, the emphasis in step motor constructions has been to have same effect an incremental rotation of the clock hands in a single direction, namely, a clockwise direction. Moreover, the emphasis in improving step motors has been in reducing the current consumption of step motors capable of effecting incremental rotation of the step motor in a fixed rotational direction and not to incrementally rotating the rotor in two directions. Accordingly, miniaturized, highly efficient step motors capable of being incorporated in a miniaturized electronic wristwatch movement and further capable of imparting incremental rotary motion in two directions have heretofore not been provided.

#For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying drawings, in which:

#FIG. 1 is a plan view of an electro-mechanical converter mechanism of an electronic wristwatch constructed in accordance with the prior art;

#FIG. 2 is a block circuit diagram illustrating the electronic movement of an electronic wristwatch constructed in accordance with the prior art;

#Reference is now made to FIG. 1, wherein a prior art electro-mechanical converter mechanism, for converting the time-keeping signals produced in an electronic wristwatch into an incremental advancement of the gear train, is depicted. The electro-mechanical converter mechanism includes a step motor comprised of an oppositely poled permanent magnet rotor 1 having two stator poles 2 and 3 disposed therearound, a stator yoke 5 connecting the respective stator poles, and a drive coil 4 having terminals 4a and 4b surrounding the yoke. The portion of the stator poles 2a and 3a, surrounding the permanent magnet rotor, are coaxially offset by an amount x with respect to the permanent magnet rotor in order to assure that the rotor is rotated in a predetermined rotational direction. Accordingly, the step motor is operated in a conventional manner by reversing the polarities of both stator poles with respect to each other to thereby effect a rotation of the magnetic rotor through a 180.degree. rotation, in response to each change of polarity of the stator poles.

#The polarity of the stator poles is alternately reversed in response to alternating the application of the same drive signal to terminals 4a and 4b of drive coil 4. The drive signal is produced by a conventional electronic timepiece movement, of the type illustrated in FIG. 2. Specifically, a high frequency time standard, such as quartz crystal vibrator 10, is coupled to an oscillator circuit for producing a high frequency time standard signal f.sub.n. A divider circuit 12, comprised of a plurality of series-connected divider stages, is adapted to receive the high frequency time standard signal produced by the oscillator circuit 11, and produce a low frequency timekeeping signal f.sub.0 in response thereto. A wave shaping circuit 13 receives the low frequency timekeeping signal f.sub.0 and applies, through leads 16 and 17 and amplifiers 14 and 15, respectively, pulse signals that are alternately applied to the drive coil 4 to thereby induce an alternating polarity signal of specific duration every second.

#Specifically, a drive signal having a pulse width of 7.8 m-sec., in duration, is applied every two seconds to the input terminal 16 of C-MOS inverter amplifier 14 and, hence, to the input terminal 4a of the drive coil 4. Additionally, every two seconds, a driving signal having a pulse width of 7.8 m-sec., in duration, is applied to input terminal 17 of C-MOS inverter 15 and, hence, to terminal 4b of the drive coil 4, to thereby alternately induce, in the drive coil 4, a driving pulse of alternating direction to thereby reverse the polarities of the stator poles of the step motor with respect to each other once each second.