1. Technical Field
The disclosed embodiments relate to clocking in integrated circuits and more particularly to pulse drive systems for clock drivers.
2. Description of the Related Art
Clock distribution networks account for a significant portion of overall power consumption in most high performance digital circuits today due to the large parasitic capacitance that is connected to the clock network. One aspect of efficient clock distribution is to ensure efficiency in various aspects of the clock system.
In some embodiments, an apparatus includes a delay circuit coupled to receive a clock signal and supply a delayed clock signal. A first transistor is coupled to receive a first pulse control signal and supply an output clock node to generate an output clock signal based in part on the first pulse control signal. An asserted edge of the first control signal is responsive to a falling edge of the delayed clock signal. A second transistor is coupled to receive a second control signal and to supply the output clock node to generate the output clock signal based in part on the second pulse control signal. An asserted edge of the second control signal is responsive to a rising edge of the delayed clock signal.
In another embodiment, a method includes delaying a clock signal in a delay circuit supplying a delayed clock signal, asserting a first pulse control signal responsive to a falling edge of the delayed clock signal, supplying the first pulse control signal to a first transistor as a first gate signal, asserting a second pulse control signal responsive to a rising edge of the delayed clock signal, and supplying the second pulse control signal to the second first transistor as a second gate signal.
In another embodiment, a non-transitory computer-readable medium stores a computer readable data structure encoding a functional description of an integrated circuit. The integrated circuit includes a resonant clock network, a delay circuit coupled to receive a clock signal and supply a delayed clock signal, a first transistor coupled to receive a first pulse control signal as a first gate signal and supply an output clock node, wherein an asserted edge of the first control signal is responsive to a falling edge of the delayed clock signal. A second transistor is coupled to receive a second control signal as a second gate signal and to supply the output clock node, wherein an asserted edge of the second control signal is responsive to a rising edge of the delayed clock signal. A first current carrying terminal of the first transistor is coupled to a first power supply and a second current carrying terminal of the first transistor is coupled to a clock output signal node. A first carrying terminal of the second transistor is coupled to a second power supply and a second current carrying terminal of the second transistor is coupled to the clock output signal node.
The embodiments disclosed herein may be better understood, and its numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings.
The use of the same reference symbols in different drawings indicates similar or identical items.
One promising technique to implement more energy-efficient clock distribution is the use of resonant clocking.
The energy losses in the resonant clock network of
Referring to
One way to improve the pulse drive system is to change the mechanism by which the delay chain impacts the duty cycle of the pulses that drive the clock driver. As described in more detail herein, some embodiments provide a more effective method for pulse mode drive that enables efficient resonant clock operation, is robust to process variation, supports multi-core supply voltage scaling, and supports clock duty cycle tuning for performance optimization in a microprocessor system.
An embodiment of such a system is illustrated in
In contrast to the pulse drive system illustrated in
To maintain an efficiently driven, full amplitude clock waveform, the pulse duty cycle typically needs to be in the 30-40% range. A 30-40% duty cycle for the control pulses is desirable for reduced jitter degradation. To obtain the required 30-40% duty cycle range, the delay chain delay implemented in the embodiment of
The embodiment illustrated in
Modern microprocessors also have to meet phase timing paths arising from the use of dynamic logic or latch-based-designs, which rely on the two phases of the clock to perform computation. A common performance optimization is therefore to vary the duty cycle of the PLL, which propagates to the output of the drivers, and allows for improved performance. The embodiment illustrated in
Most existing microprocessors use a common power supply plane to power all their cores, so that the voltage that is applied to the cores is determined by the core running at the maximum frequency. Often this implies that a core is made to run at a voltage higher than dictated by its frequency (because some other core is running faster). In the pulse drive system of
While the description has contemplated being used in clock networks of microprocessors, embodiments are not limited to microprocessors. Instead the concepts and advantages described herein apply to integrated circuits in general, where voltage margining is required to ensure robust operation in the field.
While circuits and physical structures have been generally presumed in describing embodiments of the invention, it is well recognized that in modern semiconductor design and fabrication, physical structures and circuits may be embodied in a computer readable medium as data structures for use in subsequent design, simulation, test, or fabrication stages. For example, such data structures may encode a functional description of circuits or systems of circuits. The functionally descriptive data structures may be, e.g., encoded in a register transfer language (RTL), a hardware description language (HDL), in Verilog, or some other language used for design, simulation, and/or test. Data structures corresponding to embodiments described herein may also be encoded in, e.g., Graphic Database System II (GDSII) data, and functionally describe integrated circuit layout and/or information for photomask generation used to manufacture the integrated circuits. Other data structures, containing functionally descriptive aspects of embodiments described herein, may be used for one or more steps of the manufacturing process.
Computer-readable media include tangible computer readable media, e.g., a disk, tape, or other magnetic, optical, or electronic storage medium. In addition to computer-readable medium having encodings thereon of circuits, systems, and methods, the computer readable media may store instructions as well as data that can be used to implement embodiments described herein or portions thereof. The data structures may be utilized by software executing on one or more processors, firmware executing on hardware, or by a combination of software, firmware, and hardware, as part of the design, simulation, test, or fabrication stages.
The description of the invention set forth herein is illustrative, and is not intended to limit the scope of the invention as set forth in the following claims. For example, embodiments of the invention are not limited in scope to microprocessors. Rather, the solution described herein applies to integrated circuits in general, where voltage margining is required to ensure robust operation in the field. Other variations and modifications of the embodiments disclosed herein may be made based on the description set forth herein, without departing from the scope of the invention as set forth in the following claims.
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U.S. Appl. No. 13/601,138, filed Aug. 31, 2012, entitled “Transitioning from Resonant Clocking Mode to Conventional Clocking Mode,” naming inventors Visvesh S. Sathe and Samuel Naffziger. |
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Number | Date | Country | |
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20140062565 A1 | Mar 2014 | US |