We review a few type of single flux quantum logic (SFQL) and discuss m
erits and defects of each circuit. At the same time, a new type of SFQ
L is gave an outline. The new circuit is a level logic system and oper
ates in a non-latching mode like a semiconductor FET circuit. We also
mention problems to be solved when SFQL is fabricated by using a high
temperature superconductive material.