Abstract A superconducting circuit including at least two DC SQUID stages (10, 10') integrated on the same superconducting chip and coupled by a circuit (28) providing efficient transfer of current from the first SQUID stage (10) to the second SQUID stage (10') with large bandwidth. Each SQUID stage is comprised of a superconducting loop (12) having at least two Josephson devices (J1, J2) therein, therebeing shunt resistors (R.) across the Josephson devices to render them nonhysteretic. The coupling means (28) between stages is directly connected to the shunt resistors of the first stage and includes a transmission line and an impedance circuit for measuring the impedance of the transmission line (30), where the impedance circuit provides a real impedance over a large frequency range up to approximately the frequency of Josephson oscillation of the Josephson devices in the DC SQUID. Feedback from the second SQUID stage to the first SQUID stage can be provided to improve the input dynamic range and the linearity of the circuit.
Superconducting SQUID circuit comprising a DC SQUID stage (10) including a superconducting loop with at least two Josephson devices (Jl, J2), each shunted with a resistor (R ) to render the devices nonhysteretic, means (26) for providing a DC current to the loop, input means (16) for applying input signals to the SQUID, and an output terminal (3) for delivering output currents from the SQUID, characterized in that coupling means are provided which connect the output terminal (3) of the SQUID to the input of a current sensitive or magnetic field sensitive device (10'), these coupling means including a transmission line (30) connected to the shunt resistors (R ) and a s filter (28) for providing a real impedance and for preventing the transmission of high frequency oscillations, the filter having an impedance that is matched with that of the transmission line.
Claim 2
Dependent Claim
142 words
Superconducting SQUID circuit comprising a DC SQUID stage (10) including a superconducting loop with at least two Josephson devices (Jl, J2), each shunted with a resistor (R ) to render the devices nonhysteretic, means (26) for providing a DC current to the loop, input means (16) for applying input signals to the SQUID, and an output terminal (3) for delivering output currents from the SQUID, characterized in that coupling means are provided which connect the output terminal (3) of the SQUID to the input of a current sensitive or magnetic field sensitive device (10'), these coupling means including a transmission line (30) connected to the shunt resistors (R ) and a s filter (28) for providing a real impedance and for preventing the transmission of high frequency oscillations, the filter having an impedance that is matched with that of the transmission line.
Claim 3
Dependent Claim
24 words
A circuit as claimed in claim 1, characterized in that the current or magnetic field sensitive device (10') is a second DC biased SQUID.
Claim 4
Dependent Claim
32 words
A circuit as claimed in claim 2, characterized in that a feedback path (34) is provided connecting the output of the second SQUID stage to the input of the first SQUID stage.
Claim 5
Dependent Claim
16 words
A circuit as claimed in claim 1, characterized in that the Josephson devices are tunnel junctions.
Claim 6
Dependent Claim
34 words
A circuit as claimed in claim 4, characterized in that the filter (28) is comprised of a RLC network having a substantially real impedance up to the frequencies of oscillation of the tunnel junctions.
Claim 7
Dependent Claim
47 words
A circuit as claimed in claim 1, characterized in that the shunt resistors (R ) are included in a network arranged in parallel with the Josephson devices and that the coupling means (28, 30) are electrically connected to that network at a node between the shunt resistors.
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