Regeneration Analysis of Junction Transistor Multivibrators

The two-transistor, collector-coupled relaxation circuit is a prototype configuration from which various switching circuits such as monostable multivibrators and flip-flops can be derived. Although the operational possibilities derived from the basic configuration, e.g., astable, monostable, or bistable, may differ in the details of triggering and stable point operation, the circuits of this class will have in common the key factor of the regenerative switching behavior. In addition, the circuits will have similar transient behavior immediately following the regeneration, having to do with the drive of one transistor off and the other into saturation. The operation of the transistors for a complete cycle of operation can be divided into regions, each region of which can be characterized by an approximate linear equivalent circuit. Hence, a piece-wise linear analysis can be made of the operation of these circuits. In this paper, attention will be centered on the analysis of the regenerative switching mechanism which occurs when the transistors are in the active region. A major result of the analysis is the derivation of a simple formula for the switching time. The analysis also provides a fundamental inequality which must be satisfied in order to obtain regenerative switching. An extension of the results leads to an expression for the maximum repetition frequency. In setting up the regeneration analysis, elementary design data are established. From this data, a minimum value for can be specified if sharp, rectangular output waveforms are desired.