The Research And Implementation Of Superconductive CPU And CMOS SRAM Interface Circuit

As the feature size of integrated circuits is approaching the physical limits of silicon materials,Moore's Law is no longer applicable,and at the same time,the information industry is increasingly demanding high-speed and high-performance chips.Therefore,looking for semiconductor materials and other materials that can replace silicon materials has become a hot direction in this field.For example,new semiconductor materials,such as gallium nitride,gallium arsenide and silicon carbide,have developed rapidly in recent years due to their unique advantages.In addition,superconducting computers made of superconducting materials have also become an emerging trend.Superconducting computer refers to a computer composed of superconducting subcircuits.Because superconducting materials have the characteristics of zero resistance,complete diamagnetism,and flux quantization,superconducting circuits and superconducting computers have the characteristics of low power consumption and high operating frequency.However,superconducting circuits also have certain limitations.Mainly because it is difficult to have a wide variety of functional modules like semiconductor circuits,such as large-scale memories,digital-to-analog converters,and power managers.Therefore,when superconducting circuits are used to construct complex digital computing systems,superconducting CPUs are often used as the computing cores,and some of the CPU peripherals use semiconductor circuits.At present,the superconducting circuit can only work in an environment with extremely low temperature(the working environment of the superconducting Nb process is 4.2K liquid helium environment).The voltage amplitude of the superconducting signal is very small,and it is difficult to drive the semiconductor circuit.At the same time,the information exchange between the superconducting circuit and the semiconductor circuit in the normal temperature environment will be affected by noise,which causes the superconducting signal to be easily submerged by noise.Therefore,in order to ensure the correct transmission of the superconducting signal,it is necessary to design the amplifying circuit at the superconducting circuit end to amplify the superconducting signal.The amplifying circuit is used as an interface circuit between the superconducting circuit and the semiconductor circuit,and is used to realize the information transmission from the superconducting circuit to the semiconductor circuit,especially from the superconducting CPU to the CMOS SRAM.At present,interface circuits are mainly divided into two categories,one is a nonlatching interface circuit using DC bias,and the other is a Josephson latching driver(JLD)using AC bias.This thesis mainly studies the latch-type interface circuit using AC bias.In order to realize the signal transmission from superconducting CPU to CMOS SRAM,it is required that the operating frequency of the interface circuit is not less than 1GHz and the output voltage is higher than 40 mV.In this study,a single interface circuit that meets the requirements was first realized,and on this basis,two six-channel interface circuits with output voltages of 42 mV and 52 mV were realized;then the six-channel interface circuit and CMOS SRAM were jointly debugged and tested.The interface circuit is used to control and transmit data to CMOS SRAM.In addition,in this study,JLD and superconducting linear feedback shift register(LFSR)were integrated on-chip to form an ultra-high frequency pseudo-random sequence generator that can be used for high-speed password decryption.The above experiments prove that the design as an interface circuit between superconducting CPU and semiconductor SRAM is satisfactory.After the interface circuit of this design is integrated with superconducting logic circuits such as superconducting CPU,the superconducting circuit can be directly connected with semiconductor circuit connection.In the above studies,the interface circuits are all constructed with single-stage amplification,and there are problems such as unstable operation and small working range.In the following research,in order to ensure the stability of the circuit and isolate the influence of AC bias on the circuit,this thesis designed a DC biased double flux quantum amplifier(DFQA)as the first stage of amplification,and JLD as the second stage.Amplified two-stage amplifying interface circuit.DFQA is driven by a superconducting signal,which is stable and has a large working range.The DFQA designed in this thesis can provide a DC drive current of 0.15 mA for JLD.Therefore,driven by the superconducting signal,the two-stage amplifying interface circuit can work stably,with a bias range of ±14%,which is significantly better than the single-stage amplifying interface circuit,and the operating frequency is above 1GHz.