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Monostable Multivibrators     Monostable Multivibrators     Monostable Multivibrators

Image Credit: Allied Electronics, Inc. | Digi-Key Corporation | Newark / element14


Monostable multivibrators or one-shots are digital logic devices that have only one stable state. By contrast, flip-flops and latches are bistable devices that can remain in either a set or reset state for an indefinite period of time. Monostable multivibrators remain in their stable state indefinitely, until an external input is applied. Once triggered, the output is temporarily switched to another state. Because they are timed devices, monostable multivibrators can hold their unstable output state for only a limited amount of time. With semiconductor monostable circuits, this timing function is often accomplished through the use of resistors and capacitors. In terms of a mechanical analogy, monostable multivibrators are like momentary contact pushbuttons that spring-return to a normal (stable) position when pressure is moved from the button actuator. Conversely, bistable devices such as flip-flops and latches are like standard wall or toggle switches that turn lights either on or off. 

Types of Monostable Multivibrators


There are two types of monostable multivibrators: non-retriggerable and retriggerable. Non-retriggerable devices cannot produce pulses longer than the prescribed pulse width and cannot be triggered again when the output is in the unstable state. By contrast, retriggerable devices can be triggered again when the output is in the unstable state. In terms of triggering, there are two trigger types. Negative-edge triggers can change the output on only the negative edges of the clock. By contrast, positive-edge triggers can change the output on only the positive edges of the clock. Monostable multivibrators with Schmitt triggers include circuitry to counteract spurious behavior due to noise. Some monostable multivibrators include a master reset or complementary output. Others are hardened against radiation or provide protection against electrostatic discharge (ESD).


Important Specifications

There are several important performance specifications for monostable multivibrators. Propagation delay is the time interval between the application of an input signal and the occurrence of the corresponding output. Power dissipation, the total power consumption of the device, is generally expressed in watts (W) or milliwatts (mW). Supply voltages range from - 5 V to 5 V and include intermediate voltages such as - 4.5 V, - 3.3 V, - 3 V, 1.2 V, 1.5 V, 1.8 V, 2.5 V, 3 V, 3.3 V, and 3.6 V. Operating temperature is a full-required range.


How to Select

Selecting monostable multivibrators requires an analysis of logic families. Transistor-transistor logic (TTL) and related technologies such as Fairchild advanced Schottky TTL (FAST) use transistors as digital switches. By contrast, emitter coupled logic (ECL) uses transistors to steer current through gates that compute logical functions. Another logic family, complementary metal-oxide semiconductor (CMOS), uses a combination of p-type and n-type metal-oxide-semiconductor field effect transistors (MOSFETs) to implement logic gates and other digital circuits. Bipolar CMOS (BiCMOS) is a silicon-germanium technology that combines the high speed of bipolar TTL with the low power consumption of CMOS. Other logic families for monostable multivibrators include cross-bar switch technology (CBT), gallium arsenide (GaAs), integrated injection logic (I2L) and silicon on sapphire (SOS). Gunning with transceiver logic (GTL) and gunning with transceiver logic plus (GTLP) are also available.


Packaging Options

Monostable multivibrators are available in a variety of integrated circuit (IC) package types and with different numbers of pins. Basic IC package types for ALUs include ball grid array (BGA), quad flat package (QFP), single in-line package (SIP), and dual in-line package (DIP). Many packaging variants are available. For example, BGA variants include plastic-ball grid array (PBGA) and tape-ball grid array (TBGA). QFP variants include low-profile quad flat package (LQFP) and thin quad flat package (TQFP). DIPs are available in either ceramic (CDIP) or plastic (PDIP). Other IC package types include small outline package (SOP), thin small outline package (TSOP), and shrink small outline package (SSOP). 


Related Standards