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Abstract -This article represents a novel monostable multivibrator circuit in which width and height of the pulse output can be independent electronically adjusted. In addition, the pulse width of output is not restricted to be wider or narrower than that of input pulse as conventionally employed. Namely, there is no restriction on the width of input and output pulse, the circuit's implementation is thus more convenient. The proposed circuit is composed of one MOSFET, Zener diodes, variable capacitors. The simplicity of the circuit makes it is suitable to be fabricated for integrated circuit. The results of circuit simulation is accordance well with theoretical analysis.

I. Introduction

MONOSTABLE multivibrator or one-shot timer is widely used in communication system, such as pulse position modulation, FM demodulation, clock recovery circuit. One of many conventional monostable multivibrator circuits that is typically employed for this purpose is the IC 555. It is composed of voltage comparator, timing resistor, timing capacitor and flip-flop. The basic operation of this circuit is RC series network. With the provided voltage source, the capacitor is charged and discharged where the voltage across capacitor rises and falls exponentially. When the charged voltage reaches an upper threshold level, it results in the changing of the flip-flop's state. The positive output pulse is then generated. The height of output pulse depends on the supply's voltage whereas the pulse width is directly proportional to the RC time constant. However, it is interesting to mention about some disadvantages of the conventional monostable circuits. Firstly, the input pulse width has an effect on the operation of the circuits. Namely, most circuits require the input pulse width to be either wider or narrower than the output pulse width. Secondly, the output pulse height of most circuits cannot be electronically adjusted which is important in some application.

In this project, a novel monostable multivibrator circuit is presented where its output pulse width and height can be electronically tuned. In addition, the circuit operation does not depend heavily on the input pulse width. In other words, there is no restriction between pulse width of input and output. The proposed circuit scheme is composed of resistors, zener diodes and an nmos . It is seen that the components of this circuit are fewer than that of proposed by [1]. The outline of this project will be arranged as follows. In section II, the circuit description and operation are discussed where the experimental and simulation results are given in section III. Finally the conclusion is presented in section IV

II. circuit principle

Variation in the output pulse width can be observed with the change in capacitance value. It can be made equal to the trigger width or even narrower. The height of the output pulse i.e., the pulse amplitude can be varied by varying the supply voltage level.

An equivalent circuit for 555 timer is made using a mosfet, Zener diodes. It can be used for making monostable multivibrator.

CIRCUIT DIAGRAM:

III. SIMULATION RESULTS

This circuit is designed by using zener diodes, resistors and an N-MOSFET. The standard values taken are

COMPONENTS	VALUES
RA	10K
R	10K
C	1U
C1	0.01U
C2	1U
C3	0.01U
VCC	5V
R1	500e9
R2	500e9
R3	75e3
R4	75e3
R5	75e3
R6	1e3
R7	1e3
R8	150e3
R9	500e9
R10	1e3
R11	1e3
R12	150e3
R13	150e3
R14	150e3
R15	150e3
R16	1e3
R17	150e3
R18	1e3
R19	500e9
E1	1000
E2	1000
E3	1000
E4	1000
E5	1000
E6	1000
M1
D1-D16

For these values, output of the monostable multivibrator is coming as an impulse with width of high less than the trigger input pulse width. The output waveform is:

When C = 1UF, C1 = 0.01U, C2 = 1UF, C3 = 0.1U,I.e., when C1 is reduced, the width of output pulse is reduced. The output wave form is:

C1	tp
0.01uf	20ms
0.1uf	50ms

CONCLUSION

The novel monostable multivibrator is presented in this project. The main advantage of this proposed scheme is that there is no restriction on the input's pulse width. Namely, it can be greater than that of the output's pulse width. The operation of this scheme only depends on the positive edge of the input signal. In addition, the proposed circuit can be applied for PWM, PPM, DM circuits. With the less compactness of the circuit structure, the proposed scheme can be built easily.