Digital circuit

Abstract

A digital circuit is formed by transistors operable in an unsaturated state. A pair of first transistors are connected in a differential relationship with their emitters commonly connected. A pair of second transistors are also connected in a differential relationship and have their emitters connected in common and their collectors connected respectively to the bases of the first transistors. At least one of the first transistors is connected to the bases of the second transistors to form a feedback loop. First and second current sources are connected to the emitters of the first and second transistors respectively. The state of the circuit is switched by a control signal applied to the bases of one pair of transistors.

What is claimed is: 
     
       1. A digital circuit employing transistors operable in an unsaturated state comprising: a pair of first transistors connected in a differential relationship with their emitters connected in common;   a pair of second transistors connected in a differential relationship with their emitters connected in common and with their collectors connected respectively to the bases of said first transistors, the collector of at least one of said first transistors being connected to the bases of the second transistors thereby forming a positive feedback loop between said pairs of transistors;   a first current source connected to the emitters of said first transistors;   a second current source connected to the emitters of said second transistors;   a first terminal for supplying a first constant voltage;   a first pair of resistors by which the first terminal is connected to the bases of the first transistors;   a second terminal for supplying a second constant voltage; and   a second pair of resistors by which the second terminal is connected to the bases of the second transistors;   whereby the state of the digital circuit is switched alternately in response to a control signal applied to the bases of one pair of transistors.   
     
     
       2. The circuit of claim 1, wherein the first transistors are PNP transistors and the second transistors are NPN transistors. 
     
     
       3. The circuit of claim 1, wherein the first transistors form part of a P-type current switching circuit and the second transistors form part of an N-type current switching circuit. 
     
     
       4. The circuit of claim 3, wherein each of the switching circuits includes a constant current source. 
     
     
       5. The circuit of claim 1, wherein the collector of another of the first transistors is connected to the bases of the second transistors thereby forming a second positive feedback loop. 
     
     
       6. The circuit of claim 1, further comprising a pair of additional transistors connected emitter to emitter and collector to collector to each of the first transistors respectively, the bases of the additional transistors providing additional input terminals. 
     
     
       7. The circuit of claim 6, wherein the first transistors and the additional transistors are PNP transistors.