On-chip long Josephson junction (LJJ) clock technology

Details On-chip long Josephson junction (LJJ) clock technology On-chip long Josephson junction (LJJ) clock technology

2000-06-22

2001-12-18

Grimm, Siegfried H. (Department: 2817)

Oscillators

Solid state active element oscillator

Significant distributed parameter resonator

C327S528000, C505S853000

Reexamination Certificate

active

06331805

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to on-chip clock circuits made with long Josephson junction (LJJ) technology and to clock signal distribution schemes which allow integration with rapid-single-flux-quantum (RSFQ) digital circuits and including circuits such as analog-to-digital converters realized in (RSFQ) technology.
A need exists for, on-chip, high-frequency low jitter oscillators and clock circuits which are suitable for numerous different signal processing applications.
SUMMARY OF THE INVENTION
One aspect of the invention is directed to on-chip high-frequency, low-jitter clock circuits including long Josephson junction (LJJ) oscillators usable as clock sources. The on-chip clock circuit may include a clock selector circuit and a clock distribution scheme and may be integrated with RSFQ circuits and/or with a wideband analog-to-digital converter (ADC) comparator. LJJ oscillators embodying the invention may be formed using either “linear” or “annular” long Josephson junctions. This invention enables the generation and distribution of a stable high-frequency on-chip single flux quantum (SFQ) clock. This will enable the design of a simpler and cheaper instrument prototype. Applicants' on-chip clocking scheme may have an extensive impact on all future superconducting electronic systems.
The invention also includes a new fluxon “sender” circuit suitable for synchronizing the LJJ oscillator with another oscillator, either on-chip or external to the chip. The new sender circuit may also enable the realization of a novel phase-locked loop (PLL) circuit.
In accordance with the invention, an on-chip, multi-GHz, single flux quantum (SFQ) master clock source using a long Josephson junction (LJJ) oscillator may be used to clock rapid-single-flux-quantum (RSFQ) circuits. Coupling a multi-GHz LJJ master clock coupled to an RSFQ clock decimator (e.g., a frequency divider) permits the production of clock frequencies ranging from the low GHz range to 100 or more GHz.
The invention also includes a clock selector circuit to enable transmission of SFQ clock pulses on impedance-matched striplines. The clock selector allows a user to choose between a master clock and its binary subharmonics and improves the range of operation (including the testability) of clocked digital circuits and/or analog-to-digital converter (ADC) circuitry. Although Josephson transmission lines (JTLs) are commonly used to distribute clock pulses in RSFQ circuits, they are generally unsuitable for clock distribution in the Flash ADC architecture because of the delays they introduce. To overcome this problem, applicants developed a ballistic transport of SFQ pulses on stripline transmission lines. Hybrid JTL/stripline structures that are essential for the proposed clock distribution scheme were designed and characterized. The invention may include a chip with a wideband ADC clocked with an LJJ oscillator and clock selector circuitry. A clock distribution scheme embodying the invention includes the measurement of the delay and additional jitter introduced by a JTL network. It also includes the design of a passive transmission structure using matched, low-impedance microstrip lines. It also includes the design of a hybrid transmission structure with JTLs used only for splitting the clock and microstrip lines for long-distance transmission.
Oscillators (see
FIGS. 6
,
6
A and
6
B) made with an annular long junction in accordance with the invention have some significant advantages. The annular junction has no boundary effects and may be operated to generate only one SFQ pulse per cycle. In the linear LJJ, every time a trapped fluxon hits a boundary, it reverses direction and travels to the other boundary as an antifluxon. This corresponds to a phase change of 4&pgr; and two SFQ pulses are emitted in each cycle. An annular junction is generally easier to bias and more stable than a linear junction. To use the circulating fluxon(s) in the annular junction as clock pulses, a JTL may be weakly coupled to the LJJ resonator. Resonant soliton (fluxon) oscillations in a linear LJJ may be triggered by injecting an SFQ pulse from one end. A soliton is an electromagnetic pulse that maintains its shape while propagating. A fluxon (or a quantum of magnetic flux, &PHgr;
0
=h/2e) in a long junction travelling back and forth between the two ends along the long dimension of the junction has the properties of a soliton. The term “soliton” and “fluxon” are used interchangeably, although “soliton” is more particularly used to denote a fluxon in a long Josephson junction (LJJ)


REFERENCES:
patent: 4181902 (1980-01-01), Scott

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