US 3842589 A
Description (OCR text may contain errors)
United States Patent l l Luce et al.
[ Oct. 22, 1974 I I ELECTRONIC TIMEPIECES Primary Examiner-Edith Simmons .iackmon  Inventors: Nunzio A. Luce, Trenton; George A. Attorney Agent or Frm JoeI Spwak Graham, Mercervillc Township, Mercer County, both of NJ.  ABSTRACT  Assignee: Optel Corporation, Township of An electronic timepiece such as a wrist watch of the South Brunswick, N]. type employing all solid state components including an  Filed, June 6 1973 electronic or a liquid crystal output display for indicating time, utilizes a high efficiency up-converter to en-  Appl. No.: 362,176 able a small physical and low voltage battery to provide energy for the entire electronic watch assembly  U S Cl 58/50 R S8/23 BA by applying said battery voltage to an inductor which ['51] 19/30 6 3/00 conducts current under control of a switching circuit.  Fie'ld R 23 A BA 50 R The control of current through the inductor at specifled Intervals causes a high voltage pulse train to be  References Cited developed which is then rectified to provide a higher DC voltage for providing operating potential for the UNITED STATES PATENTS entire electronic assembly of the timepiece. The sta- 3668.86 6/1 72 Dicrshock a 3 BA bility of the voltage output can be enhanced by means 37I588I 2 I973 Girurd .I 58/23 R I 3,750,383 8/1973 Kakizawa 58/23 BA of a feedback regulator.
10 Claims, 2 Drawing Figures /5 ll-4B} RECTIFIER Egg D 7 [0 22 11 a 7 24 LOGIC 33 PP MODULE SWITCHING 23 CIRCUIT CONTROL L CIRCUIT I6) I I r DRIVER I V CIRCUIT 3/ LIQLIID I CRYSTAL DIVIDERS DISPLAY r/ OSCILLATOR T ELECTRONIC TIMEPIECES BACKGROUND OF INVENTION This invention relates to a power supply for an electronic wrist watch or timepiece and more particularly to a high efficiency up-converter circuit for use in such a device.
The digital electronic wrist watch is a new development made possible by recent technological advances. The movements of mechanical timepieces, though steadily improved and miniaturized over the centuries, still have the disadvantage of wear of moving parts associated therewith. This disadvantage is eliminated in an all electronic wrist watch with no moving parts other than possibly a mechanical time setting switch used only when changing time zones or replacing the power supply of the watch since other resetting will generally be unnecessary.
The main components of an electronic liquid crystal watch are a liquid crystal display cell, a power supply, typically a 1.5 volt miniaturized battery as is presently commercially available, a crystal oscillator for timekeeping, divider circuits for dividing the primary output frequency of the crystal oscillator, counter, decoder and driver circuits for accumulating the minutes and hours and driving the liquid display cell and an upconverter for transforming the 1.5 volts supplied by the power supply to, typically about volts required for the counter, decoder and driver circuits and the liquid crystal display.
The advent of digital electronic wrist watches such as the liquid crystal watch offers improvements in accuracy, reliability and ease of reading time as compared with commonly available wrist watches. Its unavailability heretofore is due to the strigent demands imposed upon combining a liquid crystal display and the required electronics into a single small package, available at reasonably low cost, and utilizing high efficiency electronics which do not require excessive power. In
order to achieve this it is important that the power requirements and size of each part of the electronics be minimized. Available 1.5 volt compact batteries can supply 30 u-watts of power continuously for one year. For practical considerations therefore, the power dissipation of the electronics and the liquid crystal display should be less than 30 u-watts. Since a typical display cell has a power dissipation of about 15 u-watts per year with continuous use, the total power dissipation of the electronics should not exceed 15 u-watts per year with continuous use.
BRIEF DESCRIPTION OF PREFERRED EMBODIMENT In an electronic wrist watch comprising in combination, a liquid crystal display cell, a low voltage power supply, a frequency source, timekeeping and driver circuits and a voltage up-converter network for increasing the low voltage obtained from the power supply to a higher voltage for operation of the liquid crystal display cell, the improvement comprising a voltage upconverter including a relatively high Q inductor for storing energy in a magnetic field under the control of a switching circuit, operative according to a signal derived from said frequency source to thus convert said low voltage to a high voltage during one of two modes of said switching circuit.
BRIEF DESCRIPTION OF FIGURES FIG. 1 is a block diagram of an electronic timepiece employing a liquid crystal display and an up-converter circuit according to this invention.
FIG. 2 is a diagram indicating an embodiment of the control circuit and switching circuit portions of FIG. 1.
DETAILED DESCRIPTION OF FIGURES Referring to FIG. 1 there is shown a block diagram of an electronic timepiece employing a liquid crystal display.
conventionally, such timepieces employ a battery 10 which, for example, is a low voltage (1.5 volts) compact device such as those found in hearing aids, watches and so on.
The output of battery 10 may be used directly in many watches or timepieces to drive, for example, a tuning fork bias assembly or a crystal oscillator module or the voltage output of the battery may first be increased by means of an up-converter of some sort before driving various portions of the timepiece.
In any event, the electronic timepiece further includes a timing oscillator 1 1. Oscillator 11 may be crystal controlled and is a relatively stable device. Stability is necessary to assure that the time keeping functions remain accurate for long durations. The oscillator 11 has its output coupled to a plurality of dividers 12. The function of the dividers 12 are to develop lower frequency signals from the stable oscillator signal and to use these signals to develop time keeping indicia.
Thus, the oscillator signal may be at a stable frequency of 32,768HZ. The dividers 12 function to divide this frequency to provide, for example, a signal capable of manifesting pulses a minute analogous to seconds and count from this signal to develop minutes, hours, days and so on.
One skilled in the art will recognize the need for dividers and so on.
The divider module 12 may have a single output or multiple outputs shown as a single lead 14 which is coupled to counter/decoder and logic module 15.
Primarily, the function of the counter/decoder and logic module circuits 15 is to respond to the accurate divided oscillator signal to accumulate signals indicative of seconds, minutes and hours.
Thus, module 15 includes counters which may be integrated circuit configurations, which counters are controlled according to the well known principles of time keeping.
The module 15 is coupled to a driver circuit module 16 Driver circuit 16 may, for example, include a series of amplifiers as MOSFET or integrated circuit devices for amplifying signals from the counters and associated decoding circuits and applying these signals to a suitable liquid crystal display as 17.
The liquid crystal display 17 is preferably driven by a bi-directional current as is evidenced by a co-pending application entitled Liquid Crystal Driving and Switching Apparatus.
This application has issued as US. Pat. No. 3,744,049 and assigned to the assignee herein.
The liquid crystal display 17 is typically a multicharacter segmented numeric digit display cell having at least four characters. Basically, the liquid crystal cell or display 17 is well known in the art and comprises a hermetically sealed package consisting of a liquid crystal composition between two electrodes, one electrode is a common electrode for all display characters and one electrode being segmented. Segmented displays are extensively employed for all sorts of display media and are not considered part of this invention, although the drive considerations for a liquid crystal display afford to determine certain necessary features in regard to the operation of the power supply.
Namely, the liquid crystal display 17 typically requires about volts to achieve good contrast and brightness but may be operable at lower or higher voltages, e.g. 4-40 V. The power supply for the liquid crystal display can be a 15 volt battery, however, suchbatteries are not compact or if so are extremely expensive.
Hence, one must use as small a battery as possible to implement physicial and operating requirements. A battery in a digital watch should have enough energy storage to operate a watch for about one year and be small in size. Currently available batteries offer output voltages of 1.3 to 1.5 volts with capacities of 165 to 250 milliamp-hour. A single compact l.5 volt battery can supply about 30 microwatts of power continuously for one year. By using a liquid crystal display 17 and low power semiconductor circuitry, a single 1.5 volt battery will meet the power requirements. However, the voltage of 1.5 has to be increased by at least three to 10 times to operate the typical available display with low power circuits, reliability and with good brightness and contrast.
The 1.5 volt battery 10 therefore supplies power to an up-converter circuit which is an inductive charging circuit operating at high efficiency. Accordingly, battery 10 is coupled via an inductor 20 to a rectifier or diode circuit 21.
An optional capacitor 22 is shown coupled between the connection of battery 10 to inductor 20 and serves to linearize battery voltage over prolonged periods or during large temperature variations which would serve to affect the internal impedance of the battery 10. It also helps to supply the higher current through the inductor 20 during the inductor charging interval.
The inductor 20 has a relatively high Q and is selected of a value depending upon the described power and the switching rate.
Shown coupled to the connection between the inductor 20 and the rectifier 21 is a switching circuit 24. Circuit 24 may comprise a suitable transistor, junction FET or other controllable switching device. It is wellknown in the art that transistors and FETs, for example, are three terminal devices. The terminals of these devices may be termed the common electrode, output electrode, and control electrode. The switching circuit 24 serves to present a low impedance during a first state and a high impedance during a second state. Thus during the first state, the output terminal of inductor 20 is relatively grounded; and during the second state it is opened circuited or at a large impedance.
The switching circuit 24 operates between the first and second states under control of the control circuit 23, which circuit is responsive to a signal derived from the previously described divider module 12 associated with the time keeping crystal oscillator source 11. The output of the control circuit is connected to the control electrode of the switching means 24. This can clearly be seen with referenceto FIG. 2, wherein the switching circuit is shown to be a transistor, the base of which is connected to the output of the control circuit 23, the collector connected between the conductor 20 and the rectifier 21 and the emitter being common to ground.
For example, as indicated with a crystal oscillator 11, selected to operate at 32.768KHZ, the dividers 12 may be a nine stage, ripple carry binary counter. The outputs of the divider circuit may be at 256HZ and 64HZ. The 256HZ signal would be applied to the control circuit 23 to control the switching circuit 24. Therefore, the rate of operation of the switching circuit 24 may be as high as 256HZ, thus permitting a small physical capacitor 29 to be used at the output of the rectifier 21.
The switching circuit 24, if a transistor, would be selected to have a high beta and a low saturation voltage to assure efficiency.
Besides capacitor 29 coupled to the output of the rectifier 21, there is a zener diode 30. The zener 30 serves to regulate the output of the supply at l5 volts. The zener 30 may also be in series with a current sensing resistor 31. The junction between resistor 31 and zener 30 is coupled to the control circuit and will serve as a feedback control to aid in stabilizing the operation over varying circuit conditions and power requirements 33 coupling the control circuit module 23 to the rectifier 21.
As will be explained, rectifier 21 may be a synchronous rectifier and hence operate under control of the same control circuit 23 which operates the switch 24.
Synchronous control of the rectifier further increases efficiency of the unit but is not absolutely essential to operation.
OPERATION OF UP-CONVERTER The inductor 20, as indicated, is of a relatively high Q in order to minimize loss and increase efficiency.
As is well known, the current flowing through an inductor cannot change instantaneously. If one attempts to stop current flow in an inductor, a large voltage spike will be developed. The amplitude and duration of this spike or transient is a function of the magnitude of the inductor and the magnitude and rate at which the current is varied.
Basically, one can say that the larger the current and the faster the time required to stop the flow through an inductor, the larger the voltage transient produced as:
wherein V is voltage, L is inductance, i is current and t is time.
The equation being well known and well understood.
Hence, the switching circuit 24 under control of the control circuit 23 alternatively attempts to stop current flow and permit current flow through the inductor depending upon it being switched between the above described first and second states.
The rate of switching between first and second states is 256HZ, but can be higher or lower if desired (100 to 1,000HZ). The pulses obtained from control circuit are relatively narrow and may be, for example, 15 microseconds wide at a repetition rate of 256HZ.
Hence, during the first state, the switch 24 is on and therefore current from battery 10 flows through inductor and switch 24 to ground. lnductor 22 stores energy due to current flow creating a magnetic field. The amount of energy stored is, of course, dependent upon the width of the pulse which caused switch 24 to saturate or operate in the first state and, of course, the magnitude of the inductor 20 is also important. Therefore, by controlling the pulse width, one can control the energy provided.
As soon as switch 24 is turned off or to the second state, the current through the inductor has to change as the impedance to ground changes. As indicated, this change is accomplished by a voltage pulse which transfers the energy stored in the inductor 20 via the recitifier 21. Rectifier 21 produces DC from the large amplitude voltage pulse train. The rectified DC is filtered and stored across capacitor 29.
The output power is desireably controlled by means of varying the pulse repetition rate by feedback from the output zener diode to the control circuit 23 (Line 50). Essentially, the pulse repetition variation is used to control the output power. The output waveform consists of very narrow spikes having a repetition rate determined by the repetition rate of the pulse train from the dividers 12. This pulse train is modified by the control circuit such that the average power available is controlled by monitoring the output rectified voltage and varying the repetition rate according to the power required by the load. Therefore, as more power is required, the repetition rate would be decreased or the frequency would be increased. If less power is required, the opposite would be true. While pulse repetition rate is a preferred way of varying power, it is also noted that one could vary the pulse width which essentially would also serve to determine the output power. Pulse width variation could be accomplished without varying the pulse repeition rate.
If the rectifier 21 were under control of the control circuit improved operation would be provided. For example, when switch 24 is on, the rectifier 21 would be off and hence all current would flow through inductor 20 and switch 24 to therefore store the most energy possible as the shunt path through an ordinary rectifier, due to leakage and so on, is relatively reduced. The same pulse or signal that turns the switch 24 off now turns the rectifier 21 on, therefore, transferring maximum energy to capacitor 29.
Briefly, the control circuit 23 can be of the type to provide a variable width pulse for regulation and as such can be a monostable multivibrator whose pulse width could be varied as a function of the current flow via resistor 31. Therefore, as the load (counter/decoder 15, driver and liquid crystal display) power requirements increase, the current through 31 decreases. This decrease causes the control circuit to keep switch 24 in the on state longer thus storing more energy in inductor 20, thus providing more power when needed.
There are numerous configuration which can be used for the dividers 12 and control circuit 23 which are known in the art. As such, they utilize mulitvibrators, gates and so on.
In any event, the advantages of the above described up-converter being in utilizing small physical elements, under control of a clock circuit which signal is freely available in a timepiece because of time keeping functions. Thus, one can use a small voltage, compact battery and still develop large voltage for good operation of a liquid crystal display.
1. In an electronic timepiece of the type employing a relatively stable oscillator and associated frequency dividers for providing at outputs thereof respective signals of frequency rates necessary for time keeping operations, said timepiece including a low voltage supply and a liquid crystal display adapted for efficient operation at a given bias level in excess of said low voltage supply, the combination therewith of apparatus for converting said low voltage supply to said given bias level, comprising:
a. an inductor having a relatively high quality factor, said inductor having a first terminal coupled to a terminal of said low voltage supply and a second output terminal,
b. switching means, having an output electrode, a common electrode and a control electrode, said switch ing means capable of being in a first state indicative of a low impedence between said output and common electrodes, and in second state indicative of a high impedance between output and common electrodes, said states selected according to the magnitude of a control signal applied to said control electrode, said output electrode of said switching means coupled to said second output terminal of said inductor,
0. control means having an input responsive to one of said signals at one of said frequency rates provided by said dividers and an output coupled to said control electrode of said switching means for selectively causing said inductor to conduct current via said low voltage supply through said switch in said first state, and
d. utilization means coupled to said second output terminal of said inductor and responsive to said second state to develop any energy previously stored in said inductor during said first state into said given bias level necessary to operate said liquid crystal efficiently.
2. The apparatus according to claim 1 wherein said one frequency rate at which said control means is responsive is in excess of lOOHZ.
3. The apparatus according to claim 1 wherein said switching means include a transistor device having a low saturation voltage between an output collector electrode and a common emitter electrode; said transistor having a base control electrode, said collector electrode being coupled to said second output terminal of said inductor.
4. The apparatus according to claim 1 wherein said utilization means include a zener diode having a first and second electrode, said first electrode coupled to said second output terminal of said inductor and said second electrode coupled to a point of reference potential, said zener as coupled operative to conduct current to cause regulation of said bias level.
5. The apparatus according to claim 4 further including a filter capacitor in shunt with said zener diode.
6. The apparatus according to claim 1 wherein said low voltage supply is between 1 and 2 volts.
7. The apparatus according to claim 6 wherein said given bias level is between 4 to 20 volts.
8. The apparatus according to claim 1 further comprising:
a. means coupled to said utilization means and operative to monitor said bias level to provide an indicator signal when said level varies beyond a given amount, and
b. feedback means coupled to said control means and responsive to said indicator signal to vary the duration of said first state according to said indicator signal.
9. The apparatus according to claim 1 wherein said ing said second state.
10. The apparatus according to claim 9 further comprising:
a. synchronizing means coupled between said rectiutilization means include arectifier havingafirst termifier and said control means and responsive to one of nal coupled to said second output terminal of said inductor and a second terminal coupled to said liquid crystal display for applying energy to said display dursaid selected states for biasing rectifier into conduction during said one selected state.