1. A digital mixer comprising: a. a first input adapted to receive an incoming digital signal representing an oversampled representation of a corresponding analog signal; b. a second input adapted to receive a digital reference signal; and c. at least one unclocked data non-destructive readout rapid single flux quantum circuit having dual sets of input ports configured for mixing said incoming digital signal and said digital reference signal, each of said incoming digital signal and said digital reference signal being presented at respective one of said dual sets of input ports, and having a single merged output port adapted for providing an output spectrum having mixed signal products.