PULSE DUTY CONVERSION CIRCUIT

Abstract: A first electric current source (Q2) is connected to the collectors of two transistors (Q4, Q6). The base of one (Q4) of the transistors (Q4, Q6) is connected to receive an input pulse signal (Pi). The collectors of both transistors (Q4, Q6) are connected to one end of a capacitor (C). The other end of the capacitor (C) is connected to the base of a second electric current source (Q3) and the base of an output tran­ sistor (Q5). The collector potential of the output transistor (Q5) is applied to the base of the other (Q6) of the transistors (Q4, Q6), whereby the transistor (Q6) and the output transis­ tor (Q5) operate in different switching modes.

Description: Pulse duty conversion circuit This invention relates to a circuit for converting the duty of a pulse signal. Various types of pulse duty conversion circuits are known. Generally, a pulse duty conversion circuit consists of many elements and its structure is complex. Thus, such a circuit inevitably becomes large and expensive. Accordingly, it is an object of the present invention to provide a pulse duty conversion circuit which is comprised of a small number of elements and which has a simple structure. According to the present invention there is provided a pulse duty conversion circuit which comprises: a first current source means for supplying a first electric current; a second current source means for supplying a second electric current; a first transistor whose collector is connected to said first current source means, whose emitter is connected to a reference potential and whose base is connected to receive an input pulse signal; a second transistor whose collector is connected to said first current source means and whose emitter is connected to the reference potential; a third transistor whose base is connected to said second current source whose emitter is connected to the reference potential and whose collector is connected to the base of said second transistor through an impedance means and to a power source potential through a load means; and a capacitor means connected between the base of said third transistor and the collectors of the first and second transistors. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a circuit diagram of a pulse duty conversion circuit according to the present invention; Figs. 2A through 2D are timing charts of the signals supplied to various elements of the circuit shown in Fig. 1; Fig. 3 is a block diagram of a doubler circuit, a combination of the pulse duty conversion circuit of the present invention and a monostable multivibrator of a dual trigger monostable type; and Figs. 4A through 4C are timing charts of the signals supplied to the various elements of the doubler circuit shown in Fig. 3. As shown in Fig. I, a pulse duty conversion circuit according to the present invention comprises a first power source terminal 11 and a second power source terminal 12. Power source voltage Vcc is applied to the first power source terminal lI, and a predetermined reference voltage (i.e. ground potential) is applied to the second power source terminal 12. The circuit further comprises an input terminal 13 for receiving an input pulse Pi (Fig. 2A) and an output terminal 14 for supplying an output pulse (Fig. 2D). Between the first power source terminal 11 and the second power source terminal 12 a series circuit is connected which consists of a PNP transistor Q1 and a resistor R1. The base and collector of the transistor Q1 are connected to each other. The emitter of the transistor Q1 is connected to the first power source terminal 11, and the base and the collector of the transistor Q1 are connected to the second power source terminal 12 through the resistor R1. Two PNP transistors Q2 and Q3 are provided which are current mirror circuits to the transistor Q1. That is, the bases of these transistors Q2 and Q3 are connected to the base of the transistor Q1, and the emitters of these transistors Q2 and Q3 are connected to the first power source terminal 11. Between the input terminal 13 and the second power source terminal 12 a series circuit of resistors R2 and R3 is connected for applying a bias voltage. The junction of the resistors R2 and R3 is connected to the base of an NPN transistor Q4. The emitter of the transistor Q4 is connected to the ground potential, and the collector of the transistor Q4 is connected to the collector of the transistor Q2 and to the base of an NPN transistor Q5 via a capacitor C. The emitter of the transistor Q5 is connected to the reference voltage (i.e. ground potential). The collector of the transistor Q5 is connected to the output terminal 14 and also to the first power source terminal 11 through a load resistor R4. The collector of the transistor Q5 is also connected to the base of an NPN transistor Q6 through the load resistor R5. The load resistor R4 may be replaced by an impedance circuit. The collector of the transistor Q5 is connected to the collector of the transistor Q2, and the emitter of the transistor Q2 is connected to the second power source terminal 12. The function of the duty conversion circuit described above will now be described with reference to Figs. 2A through 2D. A pulse signal Pi consisting of pulses generated at intervals T (Fig. 2A) is supplied to the input terminal 11. While the potential of the signal Pi remains at a high level ("1" level), that is, for the duration of a positive input pulse, the transistor Q4 is on and its collector potential V1 falls to ground potential (ire., zero potential) as shown in Fig. 2B. When the transistor Q4 is turned on, the electric charge in the capacitor C is instantaneously discharged via the transistor Q4. The base potential V2 of the transistor Q5 then abruptly falls as shown in Fig. 2C. The transistor Q5 is thus turned off. A voltage is applied from the durst power source terminal 11 through the resistors R4 and R5 to the base of the transistor Q6. While the transistor Q5 is off and the transistor Q6 is on, the output pulse signal Po has a potential which is determined by the voltage division ratio with which the resistors R4 and R5 divide the power source voltage Vcc, said potential being a high level t"l" level). When the transistors Q5 and Q6 are turned off and on, current I2 starts flowing from the transistor Q3 to the transistor Q6 through the capacitor C. The capacitor C therefore accumulates an electric charge, and the base potential V2 of the transistor Q5 rises. When the base potential V2 reaches the base-emitter threshold voltage VBET of the transistor Q5, the transistor Q5 is turned on. The potential of the transistor Q5, i.e. the potential of the output terminal 14, falls to ground potential. Consequently, the transistor Q6 is turned off. At this time the potential of the output pulse signal Po is at a low level ( It O Ir level). If the capacitor C is electrically charged for only a period t2, the potential difference AV2 between the ends of the capacitor C is given by: I2t2/C. The charging period tl is longer than the duration of the positive pulse of the input pulse signal Pi. Hence, within the charging period t2 the potential of the input terminal 13 falls to ground potential and the transistor Q4 is turned off. When both transistors Q4 and Q5 are turned off, the capacitor C starts accumulating current I1 and is thus electrically charged opposite to the polarity with which it is charged when it accumulates current I2. As the capacitor C is electrically charged in this manner, the collector potentials of the transistors Q4 and Q6 rise. In this condition the next positive pulse of the input pulse signal Pi is applied to the input terminal 13, the transistor Q4 is turned on, and the electric charge is discharged from the capacitor C through the transistor Q4. As a result, the base potential of the transistor Q4 instantaneously falls. Thereafter, the elements of the circuit operate in the same manner as when the first positive pulse is supplied to the input terminal 13. If the capacitor C is electrically charged for only a period tl, the potential difference AV1 between the ends of the capacitor C is given as: Il tl/C. In the circuit of Fig. 1 V1 as V2 and the capacitor C has no impedance in terms of AC current. Therefore, t2 = t1 and the duty of the output pulse signal Po is 50% if I1 12. If Il \ 12, or more specifically, Il = 1 and 12 = 1 + t (Al > 0), t1 and t2 will be given: 1 = I + bI 21 + Al T t2 2I + Al Hence, the duty cycle of the output pulse signal Po can be other than 50% if I1 is not equal to I2. In other words, the duty cycle of the output pulse signal Po can be of any desired value only if currents I1 and I2 are different and the ratio of current I1 to current I2 has a proper value. In order to make currents I1 and 12 different from each other, it is sufficient to use transistors of different sizes, thus giving them different output current characteristics. Fig. 3 is a block diagram of a doubler circuit which is provided with the pulse duty conversion circuit shown in Fig. 1. Figs. 4A through 4C are timing charts of the signals supplied to various elements of the circuit shown in Fig. 3. The pulse duty conversion circuit 31 is designed to convert an input pulse signal into a pulse signal whose duty is 50%. The doubler circuit further comprises a monostable multivibrator 32 of dual trigger type. The multivibrator 32 is designed to receive an output pulse signal Po from the pulse duty conversion circuit 31 and generate two pulses as each pulse of the signal Po rises and falls. When an input pulse signal Pi, such as is shown in Fig. 4A, is supplied to the pulse duty conversion circuit 31, the circuit 31 generates an output pulse signal Po which is shown in Fig. 4B and whose duty is 50%. The pulse signal Po is supplied to the multivibrator 32. The multivibrator 32 generates two pulses in synchronism with the leading edge and trailing edge of each pulse of the signal Po. Therefore, it generates such a pulse signal Pf as shown in Fig. 4C. As evident from Figs. 4A, 4B and 4C, the pulse signal Pf has a frequency twice that of the input pulse signal Pi (Fig. 4A). The present invention is not limited to the embodiment described above. As will be well understood from the above, other embodiments are possible within the scope of the invention. For example, the current source circuit consisting of the transistors Q1, Q2 and Q3 and the resistor R1 may be replaced by any other circuit that can determine any desired ratio of the current I1 to the current I2. Further, the reference potential may be other than the ground potential, so far as it is lower than the power source potential Vcc. Still further, the NPN transistors used in the embodiment may be replaced by PNP transistors and the PNP transistors used in the embodiment may be replaced by NPN transistors. If this is the case, the power source potential VCC and the reference potential will, of course, be interchanged. As described above, the pulse duty conversion circuit according to the invention comprises only a few transistors Q4, Q5 and Q6, only one capacitor C and only two resistors R4 and R5, besides a current source circuit consisting of transistors Q1, Q2 and Q3 and a resistor R1. Its structure is simple. Yet it can convert an input pulse signal into a pulse signal of any desired pulse duty merely by changing the ratio of the current Il to the current I 2 If the pulse duty conversion circuit is combined with a monostable multivibrator of dual trigger type, its pulse duty is set to 50% and its output pulse signal is supplied to the multivibrator, a doubler circuit with a simple structure will be provided.

Claims: Claims: 1. A pulse duty conversion circuit characterized by comprising: a first current source means (Q2) for supplying a first electric current; a second current source means (Q3) for supplying a second electric current; a first transistor (Q4), the collector thereof connected to said first current source means (Q2), the emitter thereof connected to a reference potential and the base thereof connected to receive an input pulse signal; a second transistor (Q6), the collector thereof connected to said first current source (Q2) and the emitter thereof connected to the reference potential; ; a third transistor (Q5), the base thereof connected to said second current source (Q3), the emitter thereof connected to the reference potential and the collector thereof connected to the base of said second transistor (Q6) through an impedance means (R5) and to a power source potential through a load means (R4); and a capacitor means (C) connected between the base of said third transistor (Q5) and the collectors of said first and second transistors (Q4, Q6). 2. A pulse duty conversion circuit according to claim 1, characterized in that said first current source means (Q2) and said second current source means (Q3) have substantially the same output current characteristic. 3. A pulse duty conversion circuit according to claim 1, characterized in that said first current source means (Q2) and said second current source means (Q3) have different output current characteristics. 4. A pulse duty conversion circuit according to claim 1, characterized in that said first current source means (Q2) is a fourth transistor, and said second current source means (Q3) is a fifth transistor. 5. A pulse duty conversion circuit according to claim 4, characterized in that said fourth and fifth transistors are substantially the same size. 6. A pulse duty conversion circuit according to claim 4, characterized in that said fourth and fifth transistors are different in size. 7. A pulse duty conversion circuit according to claim 1, characterized in that said load means (R4) is a resistor. 8. A pulse duty conversion circuit according to claim 1, characterized in that said impedance means (R5 is a resistor. 9. A pulse conversion circuit characterized by comprising: a first current source (Q2) for supplying a first electric current; a second current source (Q3) for supplying a second electric current; a capacitor means (C) connected between said first and second current source means (Q2, Q3); a first switching means (Q4) connected between said first current source means (Q2) and a reference potential and controlled by an input pulse signal; a second switching means (Q6) connected in parallel to said first switching means (Q4); ; lnd a third switching means (Q5) connected at one end to a power source potential through a load means (R4) and at the other end to said reference potential and controlled by the potential of said capacitor means (C), the potential at one one end of said third switching means (Q5) being applied on said second switching means (Q6) through an impedance means (R5) to control said second switching means (Q6). 10. A pulse duty conversion circuit according to claim 9, characterized in that said first switching means (Q4) is a first transistor (Q4), the collector thereof connected to said first current source means (Q2), the emitter thereof connected to the reference potential and the base thereof connected to receive the input pulse signal, said second switching means (Q6) is a second transistor (Q6), the collector thereof connected to said first current source means (Q2) and the emitter thereof connected to the reference potential, and said third switching means (Q5) is a third transistor (Q5), the base thereof connected to said second current source means (Q3), the emitter thereof connected to the reference potential and the collector thereof connected to the base of said second transistor (Q6) through said impedance means (R5) and to the power source potential through the load means (R4). 11. A pulse duty conversion circuit according to claim 9, characterized in that said first current source means (Q2) and said second current source means (Q3) have substantially the same output current characteristics. 12. A pulse duty conversion circuit according to claim 9, characterized in that said first current source means (Q2) and said second current source means (Q2) have different output current characteristics. 13. A pulse duty conversion circuit according to claim 9, characterized in that said first current source moans (Q2) is a fourth transistor, and said second current source means (Q3) is a fifth transistor. 14. A pulse duty conversion circuit according to claim 13, characterized in that said fourth and fifth transistors are substantially the same size. 15. A pulse duty conversion circuit according to claim 13, characterized in that said fourth and fifth transistors are different in size. 16. A pulse duty conversion circuit according to claim 9, characterized in that said load means (R4) is a resistor. 17. A pulse duty conversion circuit according to claim 9, characterized in that said impedance means (R5) is a resistor.

Inventors: AGAWA, YASUSHI, TEZUKA, HIDEHARU
Applicants: KABUSHIKI KAISHA TOSHIBA
Application year: 1983
Main classification: H03K3
IPC codes: H03K5, H03K3