The regenerative analysis of junction-transistor multivibrators

Summary form only given, as follows. A two-transistor, collector-coupled multivibraior is representative of the class of relaxation circuits which includes most multivibrators and flip-flops. Although the specific circuits may differ in the details of triggering and stable point of operation, the circuits of this class of relaxation circuit will have in cnnmon the all important regenerative switching behavior as the circuit switches from one state to the other. In addition, the transient behavior of transistor operation immediately following the regeneration (having to do with the drive of one transistor off and the other into saturation) will be similar. The analysis of the recovery from these last mentioned effects is the treatment usually referred to as multivibrator transient analysis. Piece-wise linear approximations can be made of the transistors during a complete cycle of operations; and during the regeneration period when both transistors are traversing the active region, a simple, linear equivalent circuit is shown to be valid. Thus, a linear transient analysis of the regeneration period can be made. The analysis provides not only the rate of switching, but also simple formulas with which to calculate the actual switching time. The analysis also provides a fundamental restraint, relating transistor and passive circuit parameters, which must be satisfied to obtain regenerative switching. This restraint leads in turn to an approximate upper bound on the maximum repetition rate of the multivibrator. In setting up the regeneration analysis, elementary design data are established to obtain desired output swings, repetition rata for the astable mode and sharp rectangular waveforms. E.g., it can be shown that for a sharp, rectangular waveform, a. should be grater than approximately 0.97