Abstract: A Josephson quantizer is driven by a sinusoidal microwave generator whose output is combined with a digital two-level code representing a desired waveform. The result is to produce a bipolar drive signal of increased frequency and a bipolar Josephson output with voltage increased significantly. Output voltage is developed according to the relationship V=Nnmfs/KJ, where N is the number of junctions, n is the Josephson junction constant voltage step number, fs is the sampling frequency, m is an integer multiple of the sampling frequency and is ≧2, and KJ is the Josephson constant. The digital code generator receives the output of an improved modulator which incorporates a three-level to two-level transformation on the output of a standard three-level modulator in one embodiment. In a second embodiment, a modified two-level modulator produces a bit sequence where the polarity of the next bit is allowed to change only if there is an odd number of consecutive bits of the same polarity.