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Serial multiplier and serial spreading code generators are vital elements of the RSFQ multiuser detector. We have designed different versions of both circuits to achieve maximum speed and at the same time minimize Josephson junction count. Comparison of different serial multipliers architectures supporting signed multiplication favored for asynchronous shifting over zero circuits based on carry save adder and co-flow distribution of the partial product and the clock. A 25-bit spreading code generator supporting parallel input/output has been designed for 4 kA/cm2 (TRW) and for 1 kA/cm2 (HYPRES) processes. The corresponding maximum simulated clock speed of 52 GHz and 26 GHz and effective device area of 1×0.12 mm2 and 1.9×0.2 mm2.