Dynamic Divider Circuit

This invention relates generally to an improved dynamic divider circuit for use in an electronic timepiece and especially to a simplified dynamic divider circuit comprised of insulated gate field effect transistors. Dynamic divider circuits comprised of insulated gate field effect transistors consume significent amounts of power when operated at high frequencies. Because the size of a battery is limited in an electronic timepiece, and further because it is necessary to operate electronic timepieces at high frequencies, such divider circuits have been less than completely satisfactory.

Generally speaking, in accordance with the invention, a dynamic divider circuit comprised of inverters formed from insulated gate field effect transistors is provided. The dynamic divider circuit includes an intermediate inverter and a master and slave multiple inverters, both multiple inverters including a complementary connection of two series-connected P-channel and two series N-channel field effect transistors. The P-channel and N-channel transistors are coupled in such a manner that the output terminal of the master inverter is coupled through the intermediate inverter to the input terminal of the slave inverter, and the output terminal of the slave inverter is directly coupled to the input gate of said master inverter. A first clock pulse is supplied to the gate terminal of a further, series-connected N-channel transistor of said master inverter and to the gate terminal of a further series-connected P-channel transistor of said slave inverter. Similarly, a second clock pulse, which is the complement of said first clock pulse, is supplied to the gate terminal of a further series-connected P-channel transistor of said first inverter and the gate terminal of a further, series-connected N-channel transistor of said second inverter, the binary division of such divider circuit utilizing the parasitic capacitance generated by the field effect transistors of said first and second inverter circuits as a memory element.

Accordingly, it is an object of this invention to provide an improved dynamic divider circuit using complementary field effect transistors wherein the number of elements in such circuit is reduced.

It is a further object of this invention to provide an improved dynamic divider circuit in which current consumption is substantially reduced and in which response speed is increased.

It is still another object of this invention to provide a dynamic divider circuit wherein the parasitic capacitance at the drain terminal of said insulated gate field effect transistors provides a memory capability during the operation of said divider circuit.

Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.

The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.

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 circuit diagram of a prior art binary divider circuit;

FIG. 2 is a timing chart of the input and output voltages of the circuit of FIG. 1;

FIG. 3 is a circuit diagram of a dynamic divider circuit according to the instant invention;

FIG. 4 is a timing chart of the input and output voltages of the circuit of FIG. 3;

FIG. 5 is an equivalent circuit diagram of a prior art transmission-type binary divider circuit in operation; and

FIG. 6 is an equivalent circuit diagram of the dynamic divider circuit constructed in accordance with the instant invention.

Reference is made to FIG. 1, wherein a conventional master-slave flip-flop binary divider circuit is depicted. The divider circuit is comprised of 20 insulating gate field effect transistors and 10 N-channel insulated gate field effect transistors. As is depicted in the timing chart of FIG. 2, the binary divider circuit effects a division of the input clock pulse in such a manner when clock pulses .phi. and .phi. are applied to the multi-inverter to determine a first and second condition. In a first condition a slave inverter S is written while the master inverters M and M hold their state, and in the second condition the master inverter M is written while slave inverters S and S are held constant. As is understood, the current consumption is determined by the amount of current flowing when both channels of the inverters are simultaneously in an ON condition when the inverter stages produce a change of state. There is a further consumption of current caused by the charging and discharging of parasitic capacitance on the drain side of each transistor through the respective channel resistances. Since each insulated gate field effect transistor has approximately the same physical construction and hence the same operating characteristics, when such elements are assembled in an integrated circuit chip, current consumption is determined by the number of such elements in the chip and the rate of changing state, more accurately characterized as the frequency at which the circuit is operated. Thus, when such divider circuits are operated at high frequencies in an electronic timepiece, the small-sized batteries are not capable of sustaining the power consumption over a long period of time due to their limited capacity.

Reference is now made to FIG. 3, wherein a dynamic binary divider circuit, including an intermediate inverter, generally indicated at 2, and two multiple inverters all generally indicated at 1 and 3, is depicted. First multiple inverter 1, hereinafter referred to as the master inverter includes a complementary connection of serially connected P-channel transistors P.sub.1 and P.sub.2 to serially coupled N-channel transistors N.sub.1 and N.sub.2. Similarly, second multiple inverter 3, hereinafter referred to as the slave inverter, is comprised of a complementary connection of serially connected P-channel transistors P.sub.4 and P.sub.5 to serially connected N-channel transistors N.sub.4 and N.sub.5. Intermediate inverter 2 is comprised of a complementary connection of P-channel transistor P.sub.3 to N-channel transistor N.sub.3. The master inverter is coupled at output M, defined by the node formed by the connection of the drain terminals of transistors P.sub.2 and N.sub.2 to the input of the intermediate inverter 2, which input is defined by the node formed by the coupling of the gate terminals of transistors P.sub.3 and N.sub.3. The output M of the master inverter is defined by the node formed by the connection of the drain terminals of transistors P.sub.3 and N.sub.3 and is coupled to the input of the slave inverter defined by the node formed by the connection of the gate terminals of transistors P.sub.5 and N.sub.5. The output of the slave inverter defined by the node formed by the connection of the drain terminals of transistors P.sub.5 and N.sub.5 is directly coupled to a node of said master inverter defined by the connection of the gate terminals of transistors P.sub.2 and N.sub.2. The master and slave inverters are also directly coupled to each other by the coupling of the source terminals of P.sub.1 to P.sub.4 and N.sub.1 to N.sub.4. Finally, clock pulse .phi. is coupled to the master inverter at the gate terminal of transistor N.sub.1 and to the slave inverter at the gate terminal of transistor P.sub.4 and clock pulse .phi., is coupled to the master inverter through the gate terminal of transistor P.sub.1 and is coupled to the slave inverter through the gate terminal of transistor N.sub.4. Thus, as is understood, the condition of the master inverter M and the slave inverter S is determined by the condition of the clock pulses .phi. and .phi. in the manner depicted in FIG. 4.

In accordance with the invention, equivalent capacitors C.sub.m and C.sub.s are depicted in dotted lines in FIG. 3. Capacitors C.sub.m and C.sub.s represent the equivalent capacitance caused by the operation of the divider circuit and the characteristics of the transistor elements. Such capacitance, known as parasitic capacitance, is present at the junctions formed in the insulated gate field effect devices and by the metallic wiring of such field effect transistors. It is a feature of this invention that such equivalent capacitances found at the output terminals of the master inverter and the slave inverter are utilized as memory elements for holding the states of the inverter circuits. In actual use, the contents memorized by such capacitive elements are changed according to the actual time constant created by the leakage currents, the effective capacitance at the drain terminals, and the rate at which charging and discharging is effected. However, if the time constant is equal to or greater than the value required to sustain the state of the inverter until the next change in state dictated by the clock pulse is applied to the divider circuit, the decaying effect of the time constant has no effect on the operation of the divider circuit. Moreover, because such leakage currents at the drain terminals are of the order of 1 picoampere and the parasitic capacitance seen at such terminals is of the order of 1 picofared, generally, the time constant effected thereby for such field effect transistors is several seconds allowing the use of such divider circuits for dividing signals of up to and including 1 Hz.

Reference is made to FIG. 5, wherein an equivalent circuit of the transmission-type dynamic divider circuit of the prior art is depicted. A voltage is held, or memorized, by the parasitic capacitance C.sub.1 on the drain side of a master inverter M and a transmission transistor Tr.sub.1 when transistor Tr.sub.1 is OFF. Similarly, a voltage is memorized by the parasitic capacitance C.sub.2 which is effected at the source side of transistor Tr.sub.1 and the drain side of transistor Tr.sub.2 when transistor Tr.sub.1 is turned ON. Moreover, when transistor Tr.sub.2 is turned ON, to thereby transmit the contents held thereby to slave inverter S, the voltage applied thereto is divided in the ratio of to C.sub.1 :C.sub.2, and the operating point of the inverter can be knocked out of position. Thus, in designing transmission-type dynamic divider circuits, the design of such circuits is restricted by the need to provide a C.sub.1 much larger than C.sub.2. In condradistinction thereto, in accordance with the instant invention as depicted in FIG. 6, the Master inverter M is always connected to the input of the slave inverter S in a more direct manner, thus resulting in significantly stabilized operation up to certain frequencies and hence higher response speeds by comparison with said transmission-type dividers.

Accordingly, if the circuit depicted in FIG. 3 is utilized in an integrated circuit chip, the reduction of such a binary divider circuit from 20 elements to 10 elements yields a reduction in the current utilized by such a device of one half. Moreover, the chip size is also reduced by one half due to the necessity of utilizing fewer elements, thus reducing the cost of manufacturing such divider circuits and the space in the timepiece occupied by the chip. Finally, because less current is required, the battery life is extended. These improvements are particularly significant in effecting improved electronic wristwatches.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained, and since certain changes may be made in the above construction without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be able to fall therebetween.