Superconducting digital mixer
Digital mixers which permit mixing of asynchronous signals may be constructed of Rapid Single Flux Quantum (RSFQ) logic elements. The logic elements may include an RSFQ non-destructive readout cell (NDRO), an RSFQ D flip-flop, an RSFQ XOR circuit, and an RSFQ T flip-flop. A binary tree arrangement of T flip-flops can be used to provide in-phase and quadrature phase-divided replicas of a reference signal. The mixing elements can be either an XOR circuit, a dual port NDRO circuit functioning as a multiplexer or an RS type NDRO functioning as an AND gate. The RSFQ logic elements utilize Josephson junctions which operate in superconducting temperature domains.
1. A digital mixer comprising:
an input circuit adapted to receive an incoming signal;
a reference circuit, adapted to receive a reference signal not synchronized with said incoming signal; and
a mixing circuit adapted to mix said incoming signal and said reference signal to generate an output signal having a spectrum with mixed signal products, comprising at least one superconducting non-destructive readout cell which does not receive a clock signal;
wherein at least one of the incoming signal and the reference signal is a multibit amplitude representation digital signal, generated by a circuit comprising a plurality of elements which are configured to generate concurrent digital data signals each having respectively a different magnitude relationship to the represented multibit amplitude.
2. The digital mixer of claim 1 , wherein said mixing circuit comprises a Rapid Single Flux Quantum circuit.
3. The digital mixer of claim 2 , wherein said mixing circuit further comprises an XOR gate.
4. The digital mixer of claim 1 , wherein said mixing circuit comprises a pair of multiplexers.
5. The digital mixer of claim 1 , wherein at least one of said input and reference circuit comprises a D flip-flop.
6. The digital mixer of claim 1 , wherein at least one of said input and reference circuit comprises a T flip-flop.
7. A cross correlator using the digital mixer of claim 1 .
8. A digital receiver using the cross correlator of claim 7 .
9. A mixer for mixing a square wave reference signal with an incoming signal comprising:
a reference circuit adapted to receive said reference signal and adapted to produce a plurality of local signals with respectively different phases;
an input circuit adapted to receive said incoming signal and adapted to produce a plurality of input signals having respectively different phases;
wherein at least one of said plurality of local signals and said plurality of input signals is a multibit amplitude digital signal, generated by a circuit comprising a plurality of elements which are configured to generate concurrent digital data signals each having respectively a different magnitude relationship to the represented multibit amplitude;
a plurality of substantially unclocked mixing circuits, each adapted to receive a complementary set of said plurality of local signals and a complementary set of said plurality of input signals, each comprising a superconducting dual-port non-destructive readout cell; and
an output from each mixing circuit adapted to provide an output signal having a spectrum with mixed signal products of the incoming signal and a respective phase of the reference signal.
10. The mixer of claim 9 , wherein said plurality of mixing circuits comprise Rapid Single Flux Quantum circuits.
11. The mixer of claim 10 , wherein said plurality of mixing circuits further comprise an XOR gate.
12. The mixer of claim 9 , in which said plurality of mixing circuits each comprise a multiplexer.
13. The mixer of claim 9 , in which at least one of said reference circuit and said input circuit comprises a D flip-flop.
14. The mixer of claim 9 , in which at least one of said reference circuit and said input circuit comprises a T flip-flop.
15. A digital mixing method, comprising:
receiving an incoming signal;
receiving a reference signal not synchronized with said incoming signal; and
mixing said incoming signal and said reference signal in a mixing circuit comprising at least one superconducting non-destructive readout cell which does not receive a clock signal, to generate an output signal having a spectrum with mixed signal products;
wherein at least one of the incoming signal and the reference signal is a concurrent multibit amplitude representation digital signal, each bit of the multibit amplitude representation having respectively a different magnitude relationship to the represented multibit amplitude.
16. The method of claim 15 , wherein said mixing circuit comprises a Rapid Single Flux Quantum circuit.
17. The method of claim 16 , wherein said mixing circuit comprises an XOR gate.
18. The method of claim 15 , wherein said mixing circuit comprises a pair of multiplexers.
19. The method of claim 15 , wherein at least one of said input signal and reference signal is received from a circuit comprising a D flip-flop.
20. The method of claim 15 , wherein at least one of said input signal and reference signal is received from a circuit comprising a T flip-flop.