Four-phase logic

Last updated

Four-phase logic is a type of, and design methodology for dynamic logic. It enabled non-specialist engineers to design quite complex ICs, using either PMOS or NMOS processes. It uses a kind of 4-phase clock signal.

Contents

History

R. K. "Bob" Booher, an engineer at Autonetics, invented four-phase logic and communicated the idea to Frank Wanlass at Fairchild Semiconductor; Wanlass promoted this logic form at General Instrument Microelectronics Division. [1] Booher made the first working four-phase chip, the Autonetics DDA integrator, during February 1966; he later designed several chips for and built the Autonetics D200 airborne computer using this technique. [2]

In April 1967, Joel Karp and Elizabeth de Atley published an article, "Use four-phase MOS IC logic" in Electronic Design magazine. [3] In the same year, Cohen, Rubenstein, and Wanlass published "MTOS four phase clock systems." [4] Wanlass had been director of research and engineering at General Instrument Microelectronics Division in New York since leaving Fairchild Semiconductor in 1964.

Lee Boysel, a disciple of Wanlass [5] and a designer at Fairchild Semiconductor, and later founder of Four-Phase Systems, gave a "late news" talk on a four-phase 8-bit adder device in October 1967 at the International Electron Devices meeting. [6] J. L. Seely, manager of MOS Operations at General Instrument Microelectronics Division, also wrote about four-phase logic in late 1967. [7]

In 1968 Boysel published an article "Adder on a Chip: LSI Helps Reduce Cost of Small Machine" in Electronics magazine; [8] Four-phase papers from Y. T. Yen also appeared that year. [9] [10] Other papers followed shortly. [11]

Boysel recalls that four-phase dynamic logic allowed him to achieve 10X the packing density, 10X the speed, and 1/10 the power compared to other MOS techniques being used at the time (metal-gate saturated-load PMOS logic), using the first-generation MOS process at Fairchild. [12]

Structure

There are two types of logic gates – a '1' gate and a '3' gate. These differ only in the clock phases used to drive them. A gate can have any logic function; thus, potentially, every gate has a customized layout. An example 2-input NAND 1 gate and an inverter 3 gate, together with their clock phases (the example uses NMOS transistors), are shown below:

4phase.jpg

The ϕ1 and ϕ3 clocks need to be non-overlapping, as do the ϕ2 and ϕ4 clocks. Considering the 1 gate, during the ϕ1 clock high time (also known as the precharge time), the output C precharges up to V(ϕ1)−Vth, where Vth represents the threshold of the precharge transistor. During the next quarter clock cycle (the sample time), when ϕ1 is low, and ϕ2 is high, C either stays high (if A or B are low) or C gets discharged low (if A and B are high).

The A and B inputs must be stable throughout this sample time. The output C becomes valid during this time – and therefore, a 1 gate output can't drive another 1 gate's inputs. Hence 1 gates have to feed 3 gates, and they, in turn, have to feed 1 gates.

One more thing is useful – 2 and 4 gates. A 2 gate precharges on ϕ1 and samples on ϕ3:

2gate.png

and a 4 gate precharges on ϕ3 and samples on ϕ1.

Gate interconnection rules are: 1 gates can drive 2 gates and/or 3 gates; 2 gates can drive only 3 gates; 3 gates can drive 4 gates and/or 1 gates; 4 gates can drive only 1 gates:

4phase circle.svg

Usage

Four-phase logic works well; in particular, there are no race hazards because every combinational logic gate includes a register. It's worth noting that the layout does not require the bussing of any power supplies – only clock lines are bussed. Also, since the design technique is ratioless (cf. static logic), many designs can use minimum-size transistors.

There are some difficulties:

The first electronic calculator to be built with large-scale integrated circuits (LSI), the Sharp QT-8D from 1969, used 4-phase logic, which was fabricated by Rockwell International because Japan did not yet have the LSI technology to do it domestically. [13] 4-phase logic was also considered for use in the Intel 4004, but only Rockwell had the design tools and expertise to do large scale 4-phase ICs at that time so Intel settled on 2-phase dynamic logic instead. [14]

Evolution

With the advent of CMOS, the precharge transistor could be changed to be the complement of the logic transistor type, which allows the gate's output to charge quickly up to the high level of the clock line, thus improving the speed, signal swing, power consumption, and noise margin. This technique is used in domino logic.

Related Research Articles

<span class="mw-page-title-main">Logic gate</span> Device performing a Boolean function

A logic gate is an idealized or physical device that performs a Boolean function, a logical operation performed on one or more binary inputs that produces a single binary output.

<span class="mw-page-title-main">Microprocessor</span> Computer processor contained on an integrated-circuit chip

A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit (IC), or a small number of ICs. The microprocessor contains the arithmetic, logic, and control circuitry required to perform the functions of a computer's central processing unit (CPU). The IC is capable of interpreting and executing program instructions and performing arithmetic operations. The microprocessor is a multipurpose, clock-driven, register-based, digital integrated circuit that accepts binary data as input, processes it according to instructions stored in its memory, and provides results as output. Microprocessors contain both combinational logic and sequential digital logic, and operate on numbers and symbols represented in the binary number system.

<span class="mw-page-title-main">MOSFET</span> Type of field-effect transistor

The metal-oxide-semiconductor field-effect transistor is a type of field-effect transistor (FET), most commonly fabricated by the controlled oxidation of silicon. It has an insulated gate, the voltage of which determines the conductivity of the device. This ability to change conductivity with the amount of applied voltage can be used for amplifying or switching electronic signals. A metal-insulator-semiconductor field-effect transistor (MISFET) is a term almost synonymous with MOSFET. Another synonym is IGFET for insulated-gate field-effect transistor.

N-type metal–oxide–semiconductor logic uses n-type (-) MOSFETs to implement logic gates and other digital circuits. These nMOS transistors operate by creating an inversion layer in a p-type transistor body. This inversion layer, called the n-channel, can conduct electrons between n-type "source" and "drain" terminals. The n-channel is created by applying voltage to the third terminal, called the gate. Like other MOSFETs, nMOS transistors have four modes of operation: cut-off, triode, saturation, and velocity saturation.

<span class="mw-page-title-main">CMOS</span> Technology for constructing integrated circuits

Complementary metal–oxide–semiconductor is a type of metal–oxide–semiconductor field-effect transistor (MOSFET) fabrication process that uses complementary and symmetrical pairs of p-type and n-type MOSFETs for logic functions. CMOS technology is used for constructing integrated circuit (IC) chips, including microprocessors, microcontrollers, memory chips, and other digital logic circuits. CMOS technology is also used for analog circuits such as image sensors, data converters, RF circuits, and highly integrated transceivers for many types of communication.

<span class="mw-page-title-main">Static random-access memory</span> Type of computer memory

Static random-access memory is a type of random-access memory (RAM) that uses latching circuitry (flip-flop) to store each bit. SRAM is volatile memory; data is lost when power is removed.

<span class="mw-page-title-main">Dynamic random-access memory</span> Type of computer memory

Dynamic random-access memory is a type of random-access semiconductor memory that stores each bit of data in a memory cell, usually consisting of a tiny capacitor and a transistor, both typically based on metal–oxide–semiconductor (MOS) technology. While most DRAM memory cell designs use a capacitor and transistor, some only use two transistors. In the designs where a capacitor is used, the capacitor can either be charged or discharged; these two states are taken to represent the two values of a bit, conventionally called 0 and 1. The electric charge on the capacitors gradually leaks away; without intervention the data on the capacitor would soon be lost. To prevent this, DRAM requires an external memory refresh circuit which periodically rewrites the data in the capacitors, restoring them to their original charge. This refresh process is the defining characteristic of dynamic random-access memory, in contrast to static random-access memory (SRAM) which does not require data to be refreshed. Unlike flash memory, DRAM is volatile memory, since it loses its data quickly when power is removed. However, DRAM does exhibit limited data remanence.

<span class="mw-page-title-main">Intel 4004</span> 4-bit microprocessor

The Intel 4004 is a 4-bit central processing unit (CPU) released by Intel Corporation in 1971. Sold for US$60, it was the first commercially produced microprocessor, and the first in a long line of Intel CPUs.

In electronics and especially synchronous digital circuits, a clock signal is an electronic logic signal which oscillates between a high and a low state at a constant frequency and is used like a metronome to synchronize actions of digital circuits. In a synchronous logic circuit, the most common type of digital circuit, the clock signal is applied to all storage devices, flip-flops and latches, and causes them all to change state simultaneously, preventing race conditions.

<span class="mw-page-title-main">Federico Faggin</span> Italian-American physicist, engineer, inventor and entrepreneur

Federico Faggin is an Italian physicist, engineer, inventor and entrepreneur. He is best known for designing the first commercial microprocessor, the Intel 4004. He led the 4004 (MCS-4) project and the design group during the first five years of Intel's microprocessor effort. Faggin also created, while working at Fairchild Semiconductor in 1968, the self-aligned MOS (metal-oxide-semiconductor) silicon-gate technology (SGT), which made possible MOS semiconductor memory chips, CCD image sensors, and the microprocessor. After the 4004, he led development of the Intel 8008 and 8080, using his SGT methodology for random logic chip design, which was essential to the creation of early Intel microprocessors. He was co-founder and CEO of Zilog, the first company solely dedicated to microprocessors, and led the development of the Zilog Z80 and Z8 processors. He was later the co-founder and CEO of Cygnet Technologies, and then Synaptics.

<span class="mw-page-title-main">Masatoshi Shima</span> Japanese electronics engineer

Masatoshi Shima is a Japanese electronics engineer. He was one of the architects of the world's first microprocessor, the Intel 4004. In 1968, Shima worked for Busicom in Japan, and did the logic design for a specialized CPU to be translated into three-chip custom chips. In 1969, he worked with Intel's Ted Hoff and Stanley Mazor to reduce the three-chip Busicom proposal into a one-chip architecture. In 1970, that architecture was transformed into a silicon chip, the Intel 4004, by Federico Faggin, with Shima's assistance in logic design.

Bipolar CMOS (BiCMOS) is a semiconductor technology that integrates two semiconductor technologies, those of the bipolar junction transistor and the CMOS logic gate, into a single integrated circuit. In more recent times the bipolar processes have been extended to include high mobility devices using silicon–germanium junctions.

In computer engineering, a logic family is one of two related concepts:

<span class="mw-page-title-main">Depletion-load NMOS logic</span> Form of digital logic family in integrated circuits

In integrated circuits, depletion-load NMOS is a form of digital logic family that uses only a single power supply voltage, unlike earlier NMOS logic families that needed more than one different power supply voltage. Although manufacturing these integrated circuits required additional processing steps, improved switching speed and the elimination of the extra power supply made this logic family the preferred choice for many microprocessors and other logic elements.

In integrated circuit design, dynamic logic is a design methodology in combinational logic circuits, particularly those implemented in metal–oxide–semiconductor (MOS) technology. It is distinguished from the so-called static logic by exploiting temporary storage of information in stray and gate capacitances. It was popular in the 1970s and has seen a recent resurgence in the design of high-speed digital electronics, particularly central processing units (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 capacitive loads being transitioned are smaller so the overall power consumption of dynamic logic may be higher or lower depending on various tradeoffs. When referring to a particular logic family, the dynamic adjective usually suffices to distinguish the design methodology, e.g. dynamic CMOS or dynamic SOI design.

Four-Phase Systems was a computer company, founded by Lee Boysel and others, which built one of the earliest computers using semiconductor main memory and MOS LSI logic. The company was incorporated in February 1969 and had moderate commercial success. It was acquired by Motorola in 1981.

In the field of electronics, a technique where part of the output of a system is used at startup can be described as bootstrapping.

In semiconductor electronics fabrication technology, a self-aligned gate is a transistor manufacturing approach whereby the gate electrode of a MOSFET is used as a mask for the doping of the source and drain regions. This technique ensures that the gate is naturally and precisely aligned to the edges of the source and drain.

<span class="mw-page-title-main">PMOS logic</span> Family of digital circuits

PMOS or pMOS logic is a family of digital circuits based on p-channel, enhancement mode metal–oxide–semiconductor field-effect transistors (MOSFETs). In the late 1960s and early 1970s, PMOS logic was the dominant semiconductor technology for large-scale integrated circuits before being superseded by NMOS and CMOS devices.

<span class="mw-page-title-main">Memory cell (computing)</span> Part of computer memory

The memory cell is the fundamental building block of computer memory. The memory cell is an electronic circuit that stores one bit of binary information and it must be set to store a logic 1 and reset to store a logic 0. Its value is maintained/stored until it is changed by the set/reset process. The value in the memory cell can be accessed by reading it.

References

  1. ↑ Bassett, Ross Knox (2007). To the Digital Age: Research Labs, Start-up Companies, and the Rise of MOS Technology. JHU Press. pp. 129–130. ISBN   978-0-8018-8639-3.
  2. ↑ Booher, R. (1968). "MOS GP Computer". Managing Requirements Knowledge, International Workshop on, SAN FRANSISCO[sic]. p. 877–. doi:10.1109/AFIPS.1968.126.
  3. ↑ Karp, J.; DeAtley, E. (1967). "Use four-phase MOS IC logic". Electronic Design. 15 (7): 62–66.
    Finn, Bernard; Bud, Robert; Trischler, Helmuth (2000). Exposing electronics. CRC Press. p. 133. ISBN   978-90-5823-057-7.
  4. ↑ Cohen, L.; Rubenstin, R.; Wanlass, F. (1–3 November 1967), "MTOS four phase clock systems", Northeast Electronics Research and Engineering Meeting (NEREM) Record, vol. 9, pp. 170–1
  5. ↑ Bassett, Ross Knox (2007). To the Digital Age: Research Labs, Start-up Companies, and the Rise of MOS Technology. JHU Press. p. 122. ISBN   978-0-8018-8639-3.
  6. ↑ Boysel, L.; Kelley, J.; Cole, R. (October 1967), "MOS/LSI 8-Bit Parallel Accumulator", International Electron Devices Meeting (IEDM), vol. 15, no. 6, pp. 2–3, Bibcode:1968ITED...15..410B, doi:10.1109/T-ED.1968.16205
  7. ↑ Seely, J.L. (March 1967). "Advances in the state-of-the-art of MOS device technology". Solid State Technology. 10: 55–62. ISBN   9780070231498.
  8. ↑ Boysel, Lee L. (18 March 1968). "Adder on a Chip: LSI Helps Reduce Cost of Small Machine". Electronics . 41 (6): 119–123. ISSN   0013-5070.
  9. ↑ Yen, Y.T. (September 1968). "A Mathematical Model Characterizing Four-Phase MOS Circuits for Logic Simulation". IEEE Transactions on Computers (9): C-17. doi:10.1109/TC.1968.229140. S2CID   27138705.
  10. ↑ Yen, Y.T. (June 1969). "Intermittent Failure Problems of Four-Phase MOS Circuits". IEEE Journal of Solid-State Circuits. SC-4 (3): 107–110. Bibcode:1969IJSSC...4..107.. doi:10.1109/JSSC.1969.1049972.
  11. ↑ Hatt, R.J.; Jackets, A.E.; Jarvis, D.B. (May 1969). "Four-phase Logic Circuits using Integrated m-o-s Transistors". Mullard Technical Communication (99). ISSN   0027-3139. OCLC   2448783.
  12. ↑ Boysel, Lee (12 October 2007). "Making Your First Million (and other tips for aspiring entrepreneurs)". U. Mich. EECS Presentation / ECE Recordings. Archived from the original on 15 November 2012.
  13. ↑ "Sharp QT-8D". VintageCalculators.
  14. ↑ "The New Methodology for Random Logic Design Used in the 4004 and All the Early Intel Microprocessors: The Silicon Gate Design Methodology". The Intel 4004 Microprocessor and the Silicon Gate Technology.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.