Three-level cascode differential current switch

摘要

A three-level input voltage level conversion circuit for three-level emitter coupled logic (ECL) cascode circuit provides three unique input levels. The input voltage level conversion circuit has a level shift up circuit for the top level input, a direct input to the middle level input, and a conventional emitter follower input for the bottom level input. The shift up circuit consists of a differential pair with differential inputs to the bases of each transistor. The collectors of these transistors are coupled to the upper level of the three-level cascode logic circuit. The emitters of the differential pair are coupled to the collector of a current source transistor. The base of the current source transistor is connected to an activation potential, and the emitter is coupled through a resistor to a reference potential. The down shift is accomplished with a differential transistor pair with bases directly coupled to a differential input pair. The collectors of these transistors are coupled to a positive potential and the emitters are coupled through resistors to a reference potential. The emitters are the differential output of the circuit and are directly coupled to the lower level of the cascode circuit.