Patent Description:
Typical circuits that implement logic functions can operate based on a clock to synchronize data and/or provide a time-based flow of the logic functions. Circuits that are based on complementary metal-oxide-semiconductor (CMOS) technology can implement a clock to indicate when a given logic circuit or gate is to capture data at one or more inputs for processing or transferring the data to other logic functions. A given clock can thus provide a clock signal to a variety of devices in the circuit to provide the requisite timing information, and thus to substantially synchronize data transfer and timing functions. Other types of circuits can implement clock signals, such as reciprocal quantum logic (RQL) circuits. RQL circuits can implement timing information based on a clock that is provided, for example, as a sinusoidal signal having a substantially stable-frequency. <CIT> proposes a clock signal distribution system. <CIT> proposes a clock distribution system.

One example includes a clock distribution system.

The system includes a resonator feed network comprising a first set of resonant transmission lines and a second set of resonant transmission lines. Each of the first and second sets of resonant transmission lines can have a quantity greater than one and can be configured to propagate a clock signal. The system also includes a first resonator spine conductively coupled to the first set of resonant transmission lines, such that the first resonator spine propagates the clock signal, and a second resonator spine conductively coupled to the second set of resonant transmission lines, such that the second resonator spine propagates the clock signal. The system further includes at least one resonator rib conductively coupled to each of the first and second resonator spines. Each of the at least one resonator rib can be arranged as a standing wave resonator to propagate the clock signal.

This disclosure relates generally to computer systems, and specifically to a clock distribution system. The clock distribution system, as described herein, is arranged as a resonator "spine" and "rib" configuration. As described herein, the term "spine", as pertaining to the resonator, describes a conductor that is configured to propagate a clock signal (e.g., an in-phase or quadrature-phase clock signal). The term "rib", as pertaining to the resonator, describes a conductor that is conductively coupled to the spine and is arranged as a standing-wave resonator that propagates the clock signal. The clock distribution system can include a plurality of resonator ribs that are each conductively coupled to the same resonator spine, and thus can each separately propagate the clock signal from the resonator spine. For example, the clock distribution system can be arranged as dynamic zeroth-order resonators ("DynaZORs") that implement a resonator "spine" and "rib" configuration, such as described in <CIT> (Attorney Docket No. NG(ES)-<NUM> PRI).

The clock distribution system includes a resonator feed network that includes a plurality of resonant transmission lines that are each configured to propagate a clock signal (e.g., a sinusoidal clock signal). As an example, each of the resonant transmission lines of the resonator feed network are conductively coupled to each other and to a clock source at a first end of each of the resonant transmission lines. For example, each of the resonant transmission lines can include at least one transmission line having a predetermined length, such that each of the resonant transmission lines can have a total length of approximately one-half of a wavelength of the clock signal.

The clock distribution system also includes at least one resonator spine that is conductively coupled to at least one of the resonant transmission lines of the resonator feed network. Therefore, the resonator spine(s) can likewise propagate the clock signal. For example, the clock distribution system can include a plurality of resonator spines that are each conductively coupled to at least one of the resonant transmission lines. Each of the resonator spines can therefore be coupled to multiple resonant transmission lines (e.g., at predefined intervals along the length of the resonator spine(s). Because each of the resonant transmission lines can be coupled together at a first end and have approximately one-half wavelength total length, the distance between any two given conductive couplings of respective resonant transmission lines to the resonator spine(s) can have a total length of approximately one wavelength, and therefore approximately equal amplitude. As a result, the coupling of the resonator(s) to the resonator spine(s) can increase uniformity of amplitude of the clock signal along the length of the resonator spine(s). Furthermore, amplitude aberrations of other frequency modes of the clock signal can be suppressed to provide for further uniformity of the amplitude of the clock signal. Accordingly, amplitude variations of the clock signal resulting from frequency mode deviations based on fabrication process variations of a given integrated circuit (IC) can be mitigated.

<FIG> illustrates an example of a clock distribution system <NUM>. The clock distribution system <NUM> can be implemented in a variety of applications, such as superconducting circuits (e.g., a reciprocal quantum logic (RQL) circuits). For example, the clock distribution system <NUM> can be implemented in or as part of an integrated circuit (IC).

The clock distribution system <NUM> includes at least one resonator system <NUM>. As described herein, the term "resonator system" describes at least one resonator that includes a spine and rib architecture to propagate a clock signal CLK. As an example, the clock signal CLK can be a sinusoidal clock signal. The resonator system(s) <NUM> can be configured to provide the clock signal CLK (e.g., generated from an oscillator) to each of a respective one or more circuits <NUM> that may be distributed across an IC in which the clock distribution system <NUM> is implemented, as described herein. In the example of <FIG>, each of the resonator system(s) <NUM> includes at least one resonator feed network <NUM>, at least one resonator spine <NUM>, and at least one resonator rib <NUM>. The resonator spine(s) <NUM> are conductively coupled to at least one resonator of the resonator feed network(s) <NUM>, and the resonator rib(s) <NUM> are each conductively coupled to a given one or more of the resonator spine(s) <NUM>. Thus, the clock signal CLK, provided to the resonator feed network(s) <NUM> (e.g., from a local oscillator), can be provided to propagate through the resonator feed network(s), through the resonator spine(s) <NUM>, and through each of the respective resonator rib(s) <NUM>.

In the example of <FIG>, the circuit(s) <NUM> are coupled to the resonator rib(s) <NUM>, such as inductively via respective transformer-coupling lines, to provide a clock current ICLK to an associated one of the circuit(s) <NUM>. Therefore, the clock current ICLK can be provided to the circuit(s) <NUM> to provide functions (e.g., timing functions and/or power distribution functions) for the associated circuit(s) <NUM>. Because the circuit(s) <NUM> can be distributed across the respective IC, substantial uniformity of the clock signal CLK can provide for more accurate timing and interaction between the circuit(s) <NUM>. Furthermore, due to fabrication and process tolerance mismatches, the frequency of the clock signal CLK can vary relative to the resonant frequency of the resonant transmission lines that form the resonator feed network(s) <NUM>, the resonator spine(s) <NUM>, and the resonator rib(s) <NUM>. The frequency variations of the clock signal CLK can provide for off-resonance frequency modes of the clock signal CLK on a given IC or between separate ICs, which can vary the amplitude of the clock signal CLK along a given length of the resonator spine(s) <NUM>. To mitigate variations in amplitude along the length of the resonator spine(s) <NUM>, as described herein, there can be a multitude of different configurations of the connection of the resonant transmission lines of the resonator feed network(s) <NUM> to the respective resonator spine(s) <NUM>.

<FIG> illustrates an example of a resonator feed network <NUM>. As an example, the resonator feed network <NUM> can be coupled to a carrier supporting one or more ICs (e.g., via bump bonds) to provide the clock signal CLK to the remaining portions of a given resonator system (e.g., resonator spine(s)), as described herein. The resonator feed network <NUM> can correspond to one of the resonator feed network(s) <NUM> in the example of <FIG>. Therefore, reference is to be made to the example of <FIG> in the following description of the example of <FIG>.

The resonator feed network <NUM> includes an oscillator <NUM> configured to generate a clock signal CLK. As an example, the clock signal CLK can be a sinusoidal clock signal, and can correspond to one of the components of a quadrature RQL clock signal (e.g., an in-phase component or a quadrature-phase component). In the example of <FIG>, the resonator feed network <NUM> also includes a plurality of resonant transmission lines <NUM>. The resonant transmission lines <NUM> are demonstrated as conductively coupled together and to the oscillator <NUM> at a node <NUM> at a first end, and include respective outputs <NUM> at a second end. In the example of <FIG>, the outputs <NUM> are demonstrated as a quantity of eleven, and thus provide respective approximately identical clock signals CLKA through CLKK. However, other quantities greater than or less than eleven are possible for the clock distribution system, as described herein. As described herein, the clock signals CLKA through CLKK correspond to approximately equal copies of the clock signal CLK, and are therefore all approximately equal with respect to frequency and amplitude.

In the example of <FIG>, the resonant transmission lines <NUM> are each demonstrated as including two transmission line segments <NUM>. Each of the transmission line segments <NUM> is demonstrated as having a length of "λ/<NUM>", and thus one-quarter of the wavelength "λ" of the clock signal CLK. However, the lengths of the transmission line segments <NUM> can deviate from one quarter wavelength, and are hereinafter understood to be approximately λ/<NUM>. Therefore, the total length of each of the resonant transmission lines <NUM> is approximately λ/<NUM>, and thus approximately half the wavelength of the clock signal CLK. As a result, the length between any two of the outputs <NUM>, through a total of four of the transmission line segments <NUM>, is approximately one wavelength "λ" of the clock signal CLK. Therefore, the amplitude of the clock signal CLK at each of the outputs <NUM> is approximately equal. As described herein, the example of <FIG> is demonstrated diagrammatically, such that the distance between resonant transmission lines <NUM> at the node <NUM> is negligible (e.g., approximately zero).

As described in greater detail herein, the outputs <NUM> of the resonant transmission lines <NUM> are coupled to the resonator spine(s) of the clock distribution system. For example, the resonant transmission lines <NUM> can include two separate λ/<NUM> length transmission line segments <NUM>, as demonstrated in the example of <FIG>, to improve frequency and amplitude response of the resonator <NUM>. As an example, there can be an impedance mismatch between the transmission line segment <NUM> that is coupled to resonator spine at the respective output <NUM> and the transmission line segment <NUM> coupled to the oscillator <NUM> (and the other resonant transmission lines <NUM>). However, the resonant transmission lines <NUM> can instead include transmission line segments of other lengths, such as a single λ/<NUM> length transmission line segment, or any other even multiple of λ/<NUM> length transmission line segments.

<FIG> illustrates another example of a clock distribution system <NUM>. The clock distribution system <NUM> can correspond to a portion of the clock distribution system <NUM> in the example of <FIG>. Therefore, reference is to be made to the example of <FIG> in the following description of the example of <FIG>.

The clock distribution system <NUM> includes a plurality K of resonator spines <NUM>, where K corresponds to the eleventh one of the resonator spines <NUM>. The clock distribution system <NUM> also includes a plurality of sets of resonator ribs <NUM> that are coupled to each of the resonator spines <NUM>. As described above, the clock distribution system <NUM> can include circuits (not shown in the example of <FIG>) that are coupled (e.g., inductively) to the resonator ribs <NUM>. In the example of <FIG>, each of the resonator spines <NUM> receives the clock signal CLK, demonstrated as the respective clock signals CLKA through CLKK as described above. Therefore, each of the resonator spines <NUM> is coupled to one of the outputs <NUM> of the respective resonant transmission lines <NUM> in the example of <FIG>.

In the example of <FIG>, the clock signals CLKA through CLKK are provided at approximately a midpoint along the length of the resonator spines <NUM>. As an example, the resonator spines <NUM> can all be approximately the same length, which can be approximately equal to a wavelength λ or a multiple of the wavelength of the clock signal CLK. As a result, the resonator spines <NUM> can operate as standing-wave resonators. For example, the resonator ribs <NUM> can be conductively coupled to the respective resonator spines <NUM> at approximate antinode portions of the respective clock signals CLKA through CLKK propagating in standing-wave manner on the respective resonator spines <NUM>. Therefore, the resonator ribs <NUM> can each propagate the respective one of the clock signals CLKA through CLKK at an approximately equal amplitude to provide uniformity of the clock current ICLK to respective circuits that are coupled to the resonator ribs <NUM>.

Additionally, because each of the resonator spines <NUM> is provided a respective one of the clock signals CLKA through CLKK, the resonator spines <NUM> can propagate the clock signal CLK approximately uniformly with respect to each other, as opposed to typical resonator systems that provide a clock signal to one resonator (e.g., resonator spine) of a group of resonator spines that implement conductive cross-connections between them (e.g., through ribs or other conductors between the respective resonator spines <NUM>). For example, as described above, the length from one of the resonator spines <NUM> to any other one of the resonator spines <NUM> through the resonant transmission lines <NUM> that provide the respective clock signals CLKA through CLKK is approximately one wavelength λ of the clock signal CLK. Therefore, the resonator spines <NUM> are all conductively coupled through the resonant transmission lines <NUM>, and the amplitude of the clock signals CLKA through CLKK can be approximately uniformly applied to each of the resonator spines <NUM>. As a result, the clock distribution system <NUM> can exhibit greater uniformity of the clock signal CLK in each of the resonator spines <NUM> relative to an arrangement in which the clock signal CLK is provided to only one of the resonator spines <NUM> that are conductively coupled through cross-bars or the resonator ribs <NUM>.

The clock distribution system <NUM> includes a first resonator spine <NUM> and a second resonator spine <NUM>. The clock distribution system <NUM> also includes a plurality of sets of resonator ribs <NUM> that are coupled to each of the resonator spines <NUM> and <NUM>. As an example, the first and second resonator spines <NUM> and <NUM> can nominally be fabricated to be approximately equal in length. As a first example, each of the resonator ribs <NUM> can be coupled to the resonator spines <NUM> and/or <NUM>. As described above, the clock distribution system <NUM> can include circuits (not shown in the example of <FIG>) that are coupled (e.g., inductively) to the resonator ribs <NUM>.

The resonator spines <NUM> and <NUM> receive the clock signal CLK, demonstrated as the respective clock signals CLKA through CLKK as described above. In the example of <FIG>, the clock signals CLKA through CLKF are provided to the first resonator spine <NUM> and the clock signals CLKG through CLKK are provided to the second resonator spine <NUM>. The clock signals CLKA through CLKK can be provided at locations along the length of the resonator spines <NUM> and <NUM> at predetermined equal intervals between the sets of resonator ribs <NUM>. As an example, the intervals between each of the conductive coupling of the clock signals CLKA through CLKF to the first resonator spine <NUM> and the intervals between each of the conductive coupling of the clock signals CLKG through CLKK to the second resonator spine <NUM> can be approximately equal along the length of the respective first and second resonator spines <NUM> and <NUM>.

Based on the coupling of multiple copies of the clock signal CLK (e.g., the clock signals CLKA through CLKF to the first resonator spine <NUM> and the clock signals CLKG through CLKK to the second resonator spine <NUM>), the clock signal CLK can propagate on the first and second resonator spines <NUM> and <NUM> with a substantially more uniform amplitude along the length of the first and second resonator spines <NUM> and <NUM>, as described in greater detail herein. Furthermore, amplitude variations of the clock signal CLK resulting from additional frequency modes that are stimulated when the operating frequency differs from the as-fabricated resonant frequency of the respective first and second resonator spines <NUM> and <NUM>, and the ribs connected to the first and second resonator spines <NUM> and <NUM>, can be suppressed based on the multiple conductive couplings of the clock signal CLK to the first and second resonator spines <NUM> and <NUM>, as described in greater detail herein.

<FIG> illustrates an example diagram <NUM> of resonator spines. The resonator spines are demonstrated in the example of <FIG> as a first resonator spine <NUM> and a second resonator spine <NUM>. The first and second resonator spines <NUM> and <NUM> can correspond to approximately identical resonator spines, as described herein, to demonstrate the effects of a single coupling of the clock signal CLK to each of the first resonator spine <NUM> and the second resonator spine <NUM>. The resonator spines <NUM> and <NUM> in the example of <FIG> therefore demonstrate the relative amplitude variation of the clock signal CLK propagating therein.

In the example of <FIG>, the first and second resonator spines <NUM> and <NUM> are conductively coupled by a periodic arrangement of resonator ribs <NUM>. The first resonator spine <NUM> is demonstrated as receiving the clock signal CLKA at an approximate midpoint along the length of the first resonator spine <NUM> and the resonator spine <NUM> is demonstrated as receiving the clock signal CLKB at an approximate midpoint along the length of the second resonator spine <NUM>. Therefore, the clock signals CLKA and CLKB are conductively coupled to the respective first and second resonator spines <NUM> and <NUM> at an approximately same location along the length of the respective first and second resonator spines <NUM> and <NUM>. As an example, the clock signals CLKA and CLKB can be approximately the same, such as described above in the example of <FIG>.

In the example of <FIG>, the variation of the voltage amplitude of the clock signals CLKA and CLKB is plotted along the length of the resonator spines <NUM> and <NUM> on a graph <NUM>. Variations of the frequency of the clock signals CLKA and CLKB can result in amplitude variations of the clock signals CLKA and CLKB along the length of the resonator spines <NUM> and <NUM>. The amplitude of the clock signals CLKA and CLKB is demonstrated in the graph <NUM> as varying relative to an amplitude ICLK0 that corresponds to a frequency of the clock signals CLKA and CLKB that is equal to the resonant frequency of the first and second resonator spines <NUM> and <NUM>. Therefore, the amplitude of the clock signals CLKA and CLKB varies along the length of the resonator spines <NUM> and <NUM> based on a variation in frequency of the clock signals CLKA and CLKB relative to the resonant frequency of the resonator spines <NUM> and <NUM>.

In the example of <FIG>, the solid line amplitude in the graph <NUM> corresponds to a frequency of the clock signals CLKA and CLKB that is greater than the resonant frequency of the resonator spines <NUM> and <NUM>, and the dotted line amplitude in the graph <NUM> corresponds to a frequency of the clock signals CLKA and CLKB that is less than the resonant frequency of the resonator spines <NUM> and <NUM> (e.g., approximately equal and opposite the resonant frequency relative to the solid line). As demonstrated in the example of <FIG>, the amplitude of the clock signals CLKA and CLKB, driven above the resonant frequency of the resonator spines <NUM> and <NUM>, is demonstrated as varying along the length of the resonator spines <NUM> and <NUM> from the amplitude ICLK0 at a location of the conductive coupling of the clock signals CLKA and CLKB to the respective first and second resonator spines <NUM> and <NUM> to an amplitude ICLK1 at the distal ends of the first and second resonator spines <NUM> and <NUM>. Similarly, the amplitude of the clock signals CLKA and CLKB, driven below the resonant frequency of the resonator spines <NUM> and504, is demonstrated as varying along the length of the resonator spines <NUM> and <NUM> from the amplitude ICLK0 at a location of the conductive coupling of the clock signals CLKA and CLKB to the respective first and second resonator spines <NUM> and <NUM> to an amplitude -ICLK1 at the distal ends of the first and second resonator spines <NUM> and <NUM>. Therefore, at frequencies of the clock signals CLKA and CLKB that are greater than or less than the resonant frequency of the resonator spines <NUM> and <NUM>, the amplitude of the clock signals CLKA and CLKB can exhibit errors relative to the amplitude ICLK0 along the length of the resonator spines <NUM> and <NUM> at distances away from the conductive coupling of the clock signals CLKA and CLKB to the respective first and second resonator spines <NUM> and <NUM>.

<FIG> illustrates another example diagram <NUM> of resonator spines. The resonator spines are demonstrated in the example of <FIG> as a first resonator spine <NUM> and a second resonator spine <NUM>. The first and second resonator spines <NUM> and <NUM> can correspond to approximately identical resonator spines, as described herein, to demonstrate the effects of multiple couplings of the clock signal CLK to each of the first resonator spine <NUM> and the second resonator spine <NUM>. The resonator spines <NUM> and <NUM> in the example of <FIG> therefore demonstrate the relative amplitude variation of the clock signal CLK propagating therein.

In the example of <FIG>, the first and second resonator spines <NUM> and <NUM> are conductively coupled by a periodic arrangement of resonator ribs <NUM>. The first resonator spine <NUM> is demonstrated as receiving a clock signal CLKA and a clock signal CLKB at points approximately one quarter of the length of the first resonator spine <NUM> from the respective ends of the first resonator spine <NUM>. Similarly, the second resonator spine <NUM> is demonstrated as receiving a clock signal CLKc and a clock signal CLKD at points approximately one quarter of the length of the second resonator spine <NUM> from the respective ends of the second resonator spine <NUM>. Therefore, the clock signals CLKA and CLKC are located at approximately the same location along the lengths of the respective resonator spines <NUM> and <NUM>, and the clock signals CLKB and CLKD are located at approximately the same location along the lengths of the respective resonator spines <NUM> and <NUM>.

In the example of <FIG>, the variation of the voltage amplitude of the clock signals CLKA, CLKB, CLKC, and CLKD is plotted along the length of the resonator spines <NUM> and <NUM> on a graph <NUM>. Similar to as described above in the example of <FIG>, inherent variations of the frequency of the clock signals CLKA, CLKB, CLKC, and CLKD can result in amplitude variations of the clock signals CLKA, CLKB, CLKC, and CLKD along the length of the resonator spines <NUM> and <NUM> relative to the amplitude ICLK0 (e.g., corresponding to the resonant frequency of the first and second resonator spines <NUM> and <NUM>). Therefore, the amplitude of the clock signals CLKA, CLKB, CLKC, and CLKD varies along the length of the resonator spines <NUM> and <NUM> based on a variation in frequency of the clock signals CLKA and CLKB relative to the resonant frequency of the resonator spines <NUM> and <NUM>.

In the example of <FIG>, the solid line amplitude in the graph <NUM> corresponds to a frequency of the clock signals CLKA, CLKB, CLKC, and CLKD that is greater than the resonant frequency of the resonator spines <NUM> and <NUM>, and the dotted line amplitude in the graph <NUM> corresponds to a frequency of the clock signals CLKA, CLKB, CLKC, and CLKD that is less than the resonant frequency of the resonator spines <NUM> and <NUM> (e.g., approximately equal and opposite the resonant frequency relative to the solid line). As demonstrated in the example of <FIG>, the amplitude of the clock signals CLKA, CLKB, CLKC, and CLKD, driven above the resonant frequency of the resonator spines <NUM> and <NUM>, is demonstrated as varying along the length of the resonator spines <NUM> and <NUM> from the amplitude ICLK0 at locations of the conductive coupling of the clock signals CLKA, CLKB, CLKC, and CLKD to the respective first and second resonator spines <NUM> and <NUM> to an amplitude ICLK2 between the conductive couplings of the clock signals CLKA, CLKB, CLKC, and CLKD to the respective first and second resonator spines <NUM> and <NUM> and at the distal ends of the first and second resonator spines <NUM> and <NUM>. Similarly, the amplitude of the clock signals CLKA, CLKB, CLKC, and CLKD, driven below the resonant frequency of the resonator spines <NUM> and <NUM>, is demonstrated as varying along the length of the resonator spines <NUM> and <NUM> from the amplitude ICLK0 at locations of the conductive coupling of the clock signals CLKA, CLKB, CLKC, and CLKD to the respective first and second resonator spines <NUM> and <NUM> to an amplitude -ICLK2 between the conductive couplings of the clock signals CLKA, CLKB, CLKC, and CLKD to the respective first and second resonator spines <NUM> and <NUM> and at the distal ends of the first and second resonator spines <NUM> and <NUM>.

The amplitude ICLK2 in the example of <FIG> is less than the amplitude ICLK1 in the example of <FIG>. Therefore, the diagram <NUM> demonstrates that multiple conductive couplings of the clock signal CLK along the length of a resonator spine results in suppression of amplitude variations of the clock signal CLK resulting from frequency deviations of the clock signal CLK (e.g., relative to the resonant frequency of the respective resonator spine). Accordingly, by providing multiple couplings of the clock signal CLK to a given resonator spine, the amplitude of the clock signal CLK can exhibit greater uniformity along the length of the respective resonator spine.

Referring back to the example of <FIG>, as described above, the first and second resonator spine <NUM> and <NUM> can have an approximately equal length. The example of <FIG> demonstrates that the coupling of the clock signals CLKA through CLKF to the first resonator spine <NUM> is staggered relative to the coupling of the clock signals CLKG through CLKK to the second resonator spine <NUM>. Therefore, the coupling of a set of the resonant transmission lines <NUM> to the first resonator spine <NUM> is offset from the coupling of a set of the resonant transmission lines <NUM> to the second resonator spine <NUM> along the relative lengths of the first and second resonator spines from a first end of the each of the first and second resonator spines <NUM> and <NUM> to a second end of each of the first and second resonator spines <NUM> and <NUM>.

As also described above, at least one of the resonator ribs <NUM> in a given set of the resonator ribs <NUM> can be conductively coupled to both of the first and second resonator spines <NUM> and <NUM>. As a result, based on the relative staggered coupling of the resonant transmission lines <NUM> to the resonator spines <NUM> and <NUM>, based on the coupling of the resonator ribs <NUM> to both of the resonator spines <NUM> and <NUM>, and based on the dimensions of the resonator ribs <NUM> (e.g., approximately equal in length to a wavelength of the clock signal CLK), the amplitude variations of the clock signal CLK can be further suppressed. For example, the portions of the resonator spine <NUM> between sets of resonator ribs <NUM> that do not have a conductive coupling to a resonator <NUM> can likewise exhibit suppression of the amplitude variation of the clock signal CLK, similar to portions of the resonator spines <NUM> and <NUM> that have direct conductive coupling to the resonant transmission lines <NUM>. Accordingly, the amplitude variations of the clock signal CLK can be suppressed on multiple resonator spines based on fewer conductive couplings to resonant transmission lines of the resonator feed network, thus reducing circuit complexity and cost.

As described above, amplitude variations of the clock signal CLK resulting from additional frequency modes that deviate from the resonant frequency of a resonator spine can be suppressed based on the multiple conductive couplings of the clock signal CLK to the resonator spine. <FIG> illustrates another example diagram <NUM> of resonator spines. The resonator spines are demonstrated in the example of <FIG> as a first resonator spine <NUM> and a second resonator spine <NUM>. The first and second resonator spines <NUM> and <NUM> can correspond to approximately identical resonator spines, as described herein, to demonstrate the effects of multiple couplings of the clock signal CLK to each of the first resonator spine <NUM> and the second resonator spine <NUM>. The resonator spines <NUM> and <NUM> in the example of <FIG> therefore demonstrate the relative amplitude variation of the clock signal CLK propagating therein.

In the example of <FIG>, the first and second resonator spines <NUM> and <NUM> are conductively coupled by a periodic arrangement of resonator ribs <NUM>. The first resonator spine <NUM> is demonstrated as receiving a clock signal CLKA at a first end of the first resonator spine <NUM> and a clock signal CLKB at approximate two-thirds the length of the first resonator spine <NUM> from the first end of the first resonator spine <NUM>. Similarly, the second resonator spine <NUM> is demonstrated as receiving a clock signal CLKC at approximate one-third the length of the second resonator spine <NUM> from the first end of the second resonator spine <NUM> and a clock signal CLKD at a second end of the second resonator spine <NUM> opposite the first end. Therefore, the clock signals CLKA, CLKB, CLKC, and CLKD are staggered along the lengths of the respective resonator spines <NUM> and <NUM>, similar to as described above in the example of <FIG>.

In the example of <FIG>, the solid line amplitude in the graph <NUM> corresponds to a frequency of the clock signals CLKA, CLKB, CLKC, and CLKD that is greater than the resonant frequency of the resonator spines <NUM> and <NUM>, and the dotted line amplitude in the graph <NUM> corresponds to a frequency of the clock signals CLKA, CLKB, CLKC, and CLKD that is less than the resonant frequency of the resonator spines <NUM> and <NUM> (e.g., approximately equal and opposite the resonant frequency relative to the solid line). As demonstrated in the example of <FIG>, the amplitude of the clock signals CLKA, CLKB, CLKC, and CLKD, driven above the resonant frequency of the resonator spines <NUM> and <NUM>, is demonstrated as varying along the length of the resonator spines <NUM> and <NUM> from the amplitude ICLK0 at locations of any of the conductive coupling of the clock signals CLKA, CLKB, CLKC, and CLKD to the respective one of the first and second resonator spines <NUM> and <NUM> to an amplitude ICLK3 between any of the conductive couplings of the clock signals CLKA, CLKB, CLKC, and CLKD to the respective first and second resonator spines <NUM> and <NUM>. Similarly, the amplitude of the clock signals CLKA, CLKB, CLKC, and CLKD, driven below the resonant frequency of the resonator spines <NUM> and <NUM>, is demonstrated as varying along the length of the resonator spines <NUM> and <NUM> from the amplitude ICLK0 at any of the locations of the conductive coupling of the clock signals CLKA, CLKB, CLKC, and CLKD to the respective first and second resonator spines <NUM> and <NUM> to an amplitude -ICLK3 between any of the conductive couplings of the clock signals CLKA, CLKB, CLKC, and CLKD to the respective first and second resonator spines <NUM> and <NUM>.

The amplitude ICLK3 in the example of <FIG> is less than the amplitude ICLK2 in the example of <FIG>. Therefore, the diagram <NUM> demonstrates that multiple conductive couplings of the clock signal CLK at staggered locations along the length of multiple resonator spines relative to each other, with cross-conductive coupling via resonator ribs, results in further suppression of amplitude variations of the clock signal CLK resulting from frequency deviations of the clock signal CLK (e.g., relative to the resonant frequency of the respective resonator spine). Accordingly, by providing multiple staggered couplings of the clock signal CLK to a multiple resonator spines, with the staggering being relative to each other on the different resonator spines, the amplitude of the clock signal CLK can exhibit greater uniformity along the length of the respective resonator spines. As described above in the example of <FIG>, by providing fewer conductive couplings to resonant transmission lines of the resonator feed network, the complexity and cost of the resonator feed network that provides the clock signal CLK can be significantly reduced.

As a result of the amplitude variation suppression described herein, fabrication process tolerance mismatches that can result in changes to the frequency of the clock signal CLK and/or the resonant frequency of the respective resonator spine can be compensated for by coupling the clock signal to multiple locations along the length of the one or more resonator spines. Accordingly, similar to as described above, resonator ribs (e.g., the resonator ribs <NUM> in the example of <FIG>) can be conductively coupled at multiple locations along the length of the resonator spine <NUM> to propagate the clock signal CLK at approximately uniform amplitudes.

<FIG> illustrates an example diagram <NUM> of resonator feed networks. The diagram <NUM> include a first resonator feed network <NUM> and second resonator feed network <NUM>. As an example, the resonator feed networks <NUM> and <NUM> can be coupled to the substrate of a carrier supporting multiple ICs (e.g., via bump bonds) to provide the clock signal CLK to the remaining portions of a given resonator system (e.g., resonator spine(s) and rib(s) on multiple ICs), as described herein. The resonator feed networks <NUM> and <NUM> can correspond to one or more of the resonator feed network(s) <NUM> in the example of <FIG>. Therefore, reference is to be made to the example of <FIG> in the following description of the example of <FIG>.

The first resonator feed network <NUM> includes an oscillator <NUM> configured to generate an in-phase portion of the clock signal, demonstrated as an in-phase clock signal CLKIP. Similarly, the second resonator feed network <NUM> includes an oscillator <NUM> configured to generate a quadrature-phase portion of the clock signal, demonstrated as a quadrature-phase clock signal CLKQP. As an example, the in-phase and quadrature-phase clock signals CLKIP and CLKQP can be sinusoidal clock signals. For example, the in-phase and quadrature-phase clock signals CLKIP and CLKQP can be provided in a reciprocal quantum logic (RQL) circuit system.

In the example of <FIG>, the first resonator feed network <NUM> also includes a plurality of resonant transmission lines <NUM> and the second resonator feed network <NUM> includes a plurality of resonant transmission lines <NUM>. The resonant transmission lines <NUM> are demonstrated as conductively coupled together and to the oscillator <NUM> at a node <NUM> at a first end, and include respective outputs <NUM> at a second end. Similarly, the resonant transmission lines <NUM> are demonstrated as conductively coupled together and to the oscillator <NUM> at a node <NUM> at a first end, and include respective outputs <NUM> at a second end. In the example of <FIG>, the outputs <NUM> and <NUM> are each demonstrated as a quantity of seven, and thus provide respective approximately identical clock signals CLKA through CLKG and clock signals CLKF through CLKN, respectively. However, other quantities greater than or less than seven for each of the resonator feed networks <NUM> and <NUM> are possible for the clock distribution system, as described herein. As described herein, the clock signals CLKA through CLKG correspond to approximately equal copies of the in-phase clock signal CLKIP, and the clock signals CLKH through CLKN correspond to approximately equal copies of the quadrature-phase clock signal CLKQP. Therefore, the clock signals CLKA through CLKN are all approximately equal with respect to frequency and amplitude, with the clock signals CLKH through CLKN being approximately <NUM>° out-of-phase relative to the clock signals CLKA through CLKG.

Similar to as described above in the example of <FIG>, the resonant transmission lines <NUM> and <NUM> are each demonstrated as including two transmission line segments <NUM> that each have a length of λ/<NUM>. Therefore, the total length of each of the resonant transmission lines <NUM> and <NUM> is approximately λ/<NUM>, and thus approximately half the wavelength of the clock signal CLK. As a result, the length between any two of the outputs <NUM> or between any two of the outputs <NUM>, through a total of four of the transmission line segments <NUM>, is approximately one wavelength "λ" of the clock signals CLKIP and CLKQP.

<FIG> illustrates another example of a clock distribution system <NUM>. The clock distribution system <NUM> can correspond to a portion of the clock distribution system <NUM> in the example of <FIG>. Therefore, reference is to be made to the example of <FIG> and <FIG> in the following description of the example of <FIG>.

The clock distribution system <NUM> includes a first resonator spine <NUM>, a second resonator spine <NUM>, a third resonator spine <NUM>, and a fourth resonator spine <NUM>. The clock distribution system <NUM> also includes a plurality of sets of resonator ribs <NUM> that are each coupled to one or more of the resonator spines <NUM>, <NUM>, <NUM> and <NUM>. The resonator spines <NUM>, <NUM>, <NUM> and <NUM> can nominally be fabricated to be approximately equal in length.

The first and third resonator spines <NUM> and <NUM> receive the in-phase clock signal CLKIP, demonstrated as the respective clock signals CLKA through CLKG as described above. In the example of <FIG>, the clock signals CLKA through CLKD are provided to the first resonator spine <NUM> and the clock signals CLKE through CLKG are provided to the third resonator spine <NUM>. Similarly, the second and fourth resonator spines <NUM> and <NUM> receive the quadrature-phase clock signal CLKQP, demonstrated as the respective clock signals CLKH through CLKN as described above. The clock signals CLKH through CLKJ are provided to the second resonator spine <NUM> and the clock signals CLKK through CLKN are provided to the fourth resonator spine <NUM>.

The clock signals CLKA through CLKG can be provided at locations along the length of the resonator spines <NUM> and <NUM> and the clock signals CLKH through CLKN can be provided at locations along the length of the resonator spines <NUM> and <NUM> at predetermined equal intervals between the respective sets of resonator ribs <NUM>. As an example, the intervals between each of the conductive coupling of the clock signals CLKA through CLKN to the resonator spines <NUM>, <NUM>, <NUM>, and <NUM> can be approximately equal along the length of the respective resonator spines <NUM>, <NUM>, <NUM>, and <NUM>.

As an example, each of the resonator ribs <NUM> can be selective coupled to one or more of the resonator spines <NUM>, <NUM>, <NUM> and <NUM>, such as to propagate the in-phase clock signal CLKIP, the quadrature-phase clock signal CLKQP, or a combination (e.g., varying phase) therebetween. As described above, the clock distribution system <NUM> can include circuits (not shown in the example of <FIG>) that are coupled (e.g., inductively) to the resonator ribs <NUM>.

Each of the resonator spines <NUM>, <NUM>, <NUM>, and <NUM> can therefore suppress amplitude variations of the respective clock signals CLKIP and CLKQP, similar to as described previously. For example, based on the coupling of multiple copies of the respective clock signals CLKIP and CLKQP (e.g., the clock signals CLKA through CLKD to the first resonator spine <NUM>, the clock signals CLKH through CLKJ to the second resonator spine <NUM>, the clock signals CLKE through CLKG to the third resonator spine <NUM>, and the clock signals CLKK through CLKN to the fourth resonator spine <NUM>), the clock signals CLKIP and CLKQP can propagate with a substantially more uniform amplitude along the length of the resonator spines <NUM>, <NUM>, <NUM>, and <NUM>, as described above. Furthermore, amplitude variations of the clock signals CLKIP and CLKQP resulting from additional frequency modes that deviate from the resonant frequency of the respective first and second resonator spines <NUM>, <NUM>, <NUM>, and <NUM> can be suppressed based on the multiple conductive couplings of the clock signals CLKIP and CLKQP to the respective resonator spines <NUM>, <NUM>, <NUM>, and <NUM>, as described above.

Claim 1:
A clock distribution system (<NUM>) comprising:
a resonator feed network (<NUM>) comprising a plurality of resonant transmission lines that each propagate a clock signal;
a plurality of resonator spines (<NUM>), each of the resonator spines (<NUM>) being conductively coupled to at least one of the resonant transmission lines, such that each of the resonator spines (<NUM>) propagates the clock signal; and
at least one resonator rib (<NUM>) conductively coupled to at least two of the resonator spines (<NUM>), each of the at least one resonator rib (<NUM>) being arranged as a standing wave resonator to propagate the clock signal.