228:), or processor bus cycle extension mechanisms such as WAIT inputs, using hardware to gate the clock to a static-core CPU is simpler, is more temporally precise, uses no program code memory, and uses almost no power in the CPU while it is waiting. In a basic design, to start waiting, the CPU would write to a register to set a binary latch bit which would be ANDed or ORed with the processor clock, stopping the processor. A signal from a peripheral device would reset this latch, resuming CPU operation. The hardware logic must gate the latch control inputs as necessary to ensure that a latch output transition does not cause the clock signal level to instantaneously change and cause a clock pulse, either high or low, that is shorter than normal.
257:, and uses slow PMOS transistors for logic. Dynamic logic can be harder to work with, but it may be the only choice when increased processing speed is needed. Most electronics running at over 2 GHz these days require dynamic logic, although some manufacturers such as Intel have designed chips using completely static logic to reduce power consumption. Note that reducing power use not only extends the running time with limited power sources such as batteries or solar arrays (as in spacecraft), but it also reduces the thermal design requirements, reducing the size of needed heatsinks, fans, etc., which in turn reduces system weight and cost.
446:, as long as it functions correctly. The power dissipation can be minimized by keeping the load capacitance low. This, in turn, reduces the maximum cycle time, requiring a higher minimum clock frequency; the higher frequency then increases power consumption by the relation mentioned. Therefore, it is impossible to reduce the idle power consumption (when both inputs are high) below a certain limit derived from an equilibrium between clock speed and load capacitance.
277:
182:, there is not always a mechanism driving the output high or low. In the most common version of this concept, the output is driven high or low during distinct parts of the clock cycle. During the time intervals when the output is not being actively driven, stray capacitance causes it to maintain a level within some tolerance range of the driven level.
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are high, so that the output is low, the circuit will pump one capacitor load of charge from Vdd to ground for each clock cycle, by first charging and then discharging the capacitor in each clock cycle. This makes the circuit (with its output connected to a high impedance) less efficient than the
421:
Dynamic logic has a few potential problems that static logic does not. For example, if the clock speed is too slow, the output will decay too quickly to be of use. Also, the output is only valid for part of each clock cycle, so the device connected to it must sample it synchronously when it is
189:
fast enough that the output state of each dynamic gate is used or refreshed before the charge in the output capacitance leaks out enough to cause the digital state of the output to change, during the part of the clock cycle that the output is not being actively driven.
223:
Being able to pause a system at any time for any duration can also be used to synchronize the CPU to an asynchronous event. While there are other mechanisms to do this, such as interrupts, polling loops, processor idling input pins (for example, RDY on the
131:, in that dynamic RAM stores state dynamically as voltages on capacitances, which must be periodically refreshed. But there are also differences in usage; the clock can be stopped in the appropriate phase in a system with dynamic logic and static storage.
264:
that can be implemented in a dynamic logic based system. In addition, each rail can convey an arbitrary number of bits, and there are no power-wasting glitches. Power-saving clock gating and asynchronous techniques are much more natural in dynamic logic.
122:
circuits. For most implementations of combinational logic, a clock signal is not even needed. The static/dynamic terminology used to refer to combinatorial circuits is related to the use of the same adjectives used to distinguish memory devices, e.g.
81:(CPUs). Dynamic logic circuits are usually faster than static counterparts and require less surface area, but are more difficult to design. Dynamic logic has a higher average rate of voltage transitions than static logic, but the
399:, which represents the load capacitance of this gate, becomes charged. Because the transistor at the bottom is turned off, it is impossible for the output to be driven low during this phase.
175:; however, even in these cases, the circuit is intended to be used within a larger system where some mechanism will drive the output, and they do not qualify as distinct from static logic.
328:
260:
In general, dynamic logic greatly increases the number of transistors that are switching at any given time, which increases power consumption over static CMOS. There are several
197:—the clock can be paused indefinitely. While it may seem that doing nothing for long periods of time is not particularly useful, it leads to three advantages:
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a fully-static system can instantly resume exactly where it left off; a person doesn't have to wait for the system to boot up or resume.
159:, this principle can be rephrased as a statement that there is always a low-impedance DC path between the output and either the supply
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151:, there is always some mechanism to drive the output either high or low. In many of the popular logic styles, such as
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Besides its use of dynamic state storage via voltages on capacitances, dynamic logic is distinguished from so-called
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static version (which theoretically should not allow any current to flow except through the output), and when the
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in its implementation of combinational logic. The usual use of a clock signal is to synchronize transitions in
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are also high, the output will be pulled low. Otherwise, the output stays high (due to the load capacitance).
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being able to pause a system at any time makes debugging and testing much easier, enabling techniques such as
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of dynamic logic may be higher or lower depending on various tradeoffs. When referring to a particular
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387:. In the setup phase, the output is driven high unconditionally (no matter the values of the inputs
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246:, which improves transistor sizing optimizations. Static logic is slower because it has twice the
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When properly designed, dynamic logic can be over twice as fast as static logic. It uses only the
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235:—CPUs designed with fully static technology—are usable in space satellites owing to their higher
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are low, the output will be pulled high. At all times, the output is pulled either low or high.
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167:. As a side note, there is, of course, an exception in this definition in the case of high
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73:. It was popular in the 1970s and has seen a recent resurgence in the design of high-speed
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inputs are constant and both high, the dynamic NAND gate uses power in proportion to the
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93:, the dynamic adjective usually suffices to distinguish the design methodology, e.g.
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The largest difference between static and dynamic logic is that in dynamic logic, a
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As an example, consider the static logic implementation of a CMOS NAND gate:
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Consider now a dynamic logic implementation of the same logic function:
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The dynamic logic circuit requires two phases. The first phase, when
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Chapter 9, "Dynamic logic circuits" (chapter 7 in the 2nd edition)
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In particular, although many popular CPUs use dynamic logic, only
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Introduction to CMOS VLSI Design – Lecture 9: Circuit
Families
27:
Design methodology for combinatorial logic integrated circuits
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61:(MOS) technology. It is distinguished from the so-called
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are both high, the output will be pulled low. If either
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510:
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CMOS digital integrated circuits: analysis and design
292:
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65:by exploiting temporary storage of information in
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732:SOI design: analog, memory and digital techniques
520:SOI design: analog, memory and digital techniques
85:being transitioned are smaller so the overall
778:
759:– David Harris' lecture notes on the subject.
8:
730:Andrew Marshall; Sreedhar Natarajan (2002).
712:CMOS: Circuit Design, Layout, and Simulation
571:Bruce Jacob; Spencer Ng; David Wang (2007).
517:Andrew Marshall; Sreedhar Natarajan (2002).
208:being able to run a system at extremely low
57:circuits, particularly those implemented in
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665:
544:A. Albert Raj, T. Latha (21 October 2008).
283:This circuit implements the logic function
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771:
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908:Current mode logic / Source-coupled logic
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291:
646:. Translated by Moe, Don. Archived from
147:. In most types of logic design, termed
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690:Sung-Mo Kang; Yusuf Leblebici (2003).
550:. PHI Learning Pvt. Ltd. p. 167.
7:
323:{\displaystyle Out={\overline {AB}}}
673:"The Dark Knight: Intel's Core i7"
25:
726:Chapter 14, "Dynamic logic gates"
574:Memory systems: cache, DRAM, disk
216:to run longer on a given battery.
185:Dynamic logic requires a minimum
577:. Morgan Kaufmann. p. 270.
872:Direct-coupled transistor logic
746:Chapter 7, "Dynamic SOI Design"
604:. Morgan Kaufmann. p. 38.
493:. Academic Press. p. 37.
1:
694:(3rd ed.). McGraw-Hill.
379:, and the second phase, when
114:in that dynamic logic uses a
53:) is a design methodology in
18:Dynamic logic (digital logic)
714:(3rd ed.). Wiley-IEEE.
601:Skew-tolerant circuit design
449:A popular implementation is
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193:Static logic has no minimum
32:theoretical computer science
902:Transistor–transistor logic
135:Static versus dynamic logic
36:dynamic logic (modal logic)
977:
890:Integrated injection logic
29:
896:Resistor–transistor logic
884:Gunning transceiver logic
820:Depletion-load NMOS logic
523:. Springer. p. 125.
59:metal–oxide–semiconductor
43:integrated circuit design
626:"PocketBook II hardware"
79:central processing units
710:R. Jacob Baker (2010).
490:DSP integrated circuits
487:Lars Wanhammar (1999).
383:is high, is called the
244:faster NMOS transistors
860:Diode–transistor logic
371:is low, is called the
364:
324:
280:
262:powersaving techniques
878:Emitter-coupled logic
832:Pass transistor logic
598:David Harris (2001).
363:
353:Dynamic logic example
325:
279:
214:low-power electronics
290:
269:Static logic example
143:is used to evaluate
171:outputs, such as a
145:combinational logic
75:digital electronics
55:combinational logic
30:For the subject in
848:Other technologies
684:General references
640:"No RISC, No Fun!"
365:
320:
281:
237:radiation hardness
948:
947:
826:Complementary MOS
741:978-0-7923-7640-8
721:978-0-470-88132-3
701:978-0-07-246053-7
611:978-1-55860-636-4
584:978-0-12-379751-3
557:978-81-203-3431-1
530:978-0-7923-7640-8
500:978-0-12-734530-7
318:
87:power consumption
71:gate capacitances
16:(Redirected from
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940:Four-phase logic
822:(including HMOS)
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650:on 13 April 2013
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468:Sequential logic
425:Also, when both
404:evaluation phase
385:evaluation phase
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178:In contrast, in
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155:and traditional
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83:capacitive loads
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638:GĂĽlzow, Peter.
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51:clocked logic
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935:Domino logic
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838:Bipolar–CMOS
734:. Springer.
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654:15 September
652:. Retrieved
648:the original
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463:Domino logic
451:domino logic
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91:logic family
63:static logic
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40:
855:Diode logic
547:VLSI Design
402:During the
373:setup phase
210:clock rates
129:dynamic RAM
815:NMOS logic
810:PMOS logic
474:References
444:clock rate
255:thresholds
248:capacitive
195:clock rate
187:clock rate
125:static RAM
910:(CML/SCL)
397:capacitor
316:¯
253:, higher
169:impedance
955:Category
840:(BiCMOS)
644:AMSAT-DL
457:See also
395:). The
107:design.
102:dynamic
95:dynamic
930:Dynamic
422:valid.
375:or the
251:loading
212:allows
163:or the
161:voltage
925:Static
874:(DCTL)
828:(CMOS)
738:
718:
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608:
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165:ground
34:, see
918:Types
904:(TTL)
898:(RTL)
886:(GTL)
880:(ECL)
862:(DTL)
834:(PTL)
408:Clock
381:Clock
369:Clock
127:from
67:stray
892:(IL)
868:(OC)
736:ISBN
716:ISBN
696:ISBN
656:2021
606:ISBN
579:ISBN
552:ISBN
525:ISBN
495:ISBN
438:and
429:and
414:and
391:and
337:and
226:6502
157:CMOS
97:CMOS
69:and
345:or
333:If
153:TTL
104:SOI
100:or
41:In
957::
664:^
642:.
509:^
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406:,
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675:.
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628:.
614:.
587:.
560:.
533:.
503:.
440:B
436:A
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427:A
416:B
412:A
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389:A
347:B
343:A
339:B
335:A
312:B
309:A
303:=
300:t
297:u
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205:.
38:.
20:)
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