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61-481: Depletion-mode n-type MOSFETs as load transistors allow single voltage operation and achieve greater speed than possible with pure enhancement-load devices. This is partly because the depletion-mode MOSFETs can be a better current source approximation than the simpler enhancement-mode transistor can, especially when no extra voltage is available (one of the reasons early PMOS and NMOS chips demanded several voltages). The inclusion of depletion-mode NMOS transistors in

122-508: A ) × P ( 1 − s ) + P ( b ) × P ( s ) {\displaystyle y=P(a)\times P(1-s)+P(b)\times P(s)} , where a and b are the input bitstream and s is the select input. Using the select input = 0.5 yields: y = P ( a ) + P ( b ) 2 {\displaystyle y={\frac {P(a)+P(b)}{2}}} While this approach doesn't yield exact addition but rather scaled addition, it

183-528: A de facto standard solution to (mainly) sodium contaminants in the gates until the development of ion implantation (see below). Already by 1970, HP was making good enough nMOS ICs and had characterized it enough so that Dave Maitland was able to write an article about nMOS in the December, 1970 issue of Electronics magazine. However, NMOS remained uncommon in the rest of the semiconductor industry until 1973. The production-ready NMOS process enabled HP to develop

244-462: A demultiplexer (or demux ) is a device taking a single input and selecting signals of the output of the compatible mux , which is connected to the single input, and a shared selection line. A multiplexer is often used with a complementary demultiplexer on the receiving end. An electronic multiplexer can be considered as a multiple-input, single-output switch, and a demultiplexer as a single-input, multiple-output switch. The schematic symbol for

305-604: A NOT gate. While this is mathematically correct, a direct physical implementation would be prone to race conditions that require additional gates to suppress. Larger multiplexers are also common and, as stated above, require ⌈ log 2 ⁡ ( n ) ⌉ {\displaystyle \left\lceil \log _{2}(n)\right\rceil } selector pins for n {\displaystyle n} inputs. Other common sizes are 4-to-1, 8-to-1, and 16-to-1. Since digital logic uses binary values, powers of 2 are used (4, 8, 16) to maximally control

366-476: A certain amount of pseudo nMOS circuitry. Depletion-load processes differ from their predecessors in the way the Vdd voltage source, representing 1 , connects to each gate. In both technologies, each gate contains one NMOS transistor which is permanently turned on and connected to Vdd. When the transistors connecting to 0 turn off, this pull-up transistor determines the output to be 1 by default. In standard NMOS,

427-598: A channel length of 3 microns, which was reduced to 2 for the HMOS II, and 1.5 for HMOS III. By the time HMOS III was introduced in 1982, Intel had begun a switch to their CHMOS process, a CMOS process using design elements of the HMOS lines. One final version of the system was released, HMOS-IV. A significant advantage to the HMOS line was that each generation was deliberately designed to allow existing layouts to die-shrink with no major changes. Various techniques were introduced to ensure

488-430: A current source until the output approaches 1 , then acts as a resistor. The result is a faster 0 to 1 transition. Depletion-load circuits consume less power than enhancement-load circuits at the same speed. In both cases the connection to 1 is always active, even when the connection to 0 is also active. This results in high static power consumption. The amount of waste depends on the strength, or physical size, of

549-457: A depletion-mode MOSFET, the device is normally on at zero gate–source voltage. Such devices are used as load "resistors" in logic circuits (in depletion-load NMOS logic, for example). For N-type depletion-load devices, the threshold voltage might be about −3 V, so it could be turned off by pulling the gate 3 V negative (the drain, by comparison, is more positive than the source in NMOS). In PMOS,

610-475: A device connected that way goes as the square of the voltage across the load, it provides poor pullup speed relative to its power consumption when pulled down. A resistor (with the current simply proportional to the voltage) would be better, and a current source (with the current fixed, independent of voltage) better yet. A depletion-mode device with gate tied to the opposite supply rail is a much better load than an enhancement-mode device, acting somewhere between

671-473: A more complicated manufacturing process. MOS ICs were considered interesting but inadequate for supplanting the fast bipolar circuits in anything but niche markets, such as low power applications. One of the reasons for the low speed was that MOS transistors had gates made of aluminum which led to considerable parasitic capacitances using the manufacturing processes of the time. The introduction of transistors with gates of polycrystalline silicon (that became

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732-446: A multiplexer and demultiplexer are combined into a single piece of equipment, which is simply referred to as a multiplexer . Both circuit elements are needed at both ends of a transmission link because most communications systems transmit in both directions . In analog circuit design, a multiplexer is a special type of analog switch that connects one signal selected from several inputs to a single output. In digital circuit design,

793-432: A multiplexer is an isosceles trapezoid with the longer parallel side containing the input pins and the short parallel side containing the output pin. The schematic on the right shows a 2-to-1 multiplexer on the left and an equivalent switch on the right. The s e l {\displaystyle sel} wire connects the desired input to the output. Multiplexers are part of computer systems to select data from

854-412: A multiplexer with n selector inputs. The variables are connected to the selector inputs, and the function result, 0 or 1, for each possible combination of selector inputs is connected to the corresponding data input. If one of the variables (for example, D ) is also available inverted, a multiplexer with n -1 selector inputs is sufficient; the data inputs are connected to 0, 1, D , or ~ D , according to

915-454: A number of inputs for the given number of selector inputs. The Boolean equation for a 4-to-1 multiplexer is: Which can be expressed as a truth table : The following 4-to-1 multiplexer is constructed from 3-state buffers and AND gates (the AND gates are acting as the decoder): [REDACTED] The subscripts on the I n {\displaystyle I_{n}} inputs indicate

976-451: A resistor and a current source. The first depletion-load NMOS circuits were pioneered and made by the DRAM manufacturer Mostek , which made depletion-mode transistors available for the design of the original Zilog Z80 in 1975–76. Mostek had the ion implantation equipment needed to create a doping profile more precise than possible with diffusion methods, so that the threshold voltage of

1037-558: A similar but more robust product for the 9800 series calculators, contributed IC fabrication experience from their 4-kbit ROM project to help improve Intel DRAM’s reliability, operating-voltage, and temperature range. These efforts contributed to the heavily enhanced Intel 1103 1-kbit pMOS DRAM, which was the world’s first commercially available DRAM IC. It was formally introduced in October 1970, and became Intel’s first really successful product. Early MOS logic had one transistor type, which

1098-451: A simple demultiplexer; and while the demultiplexing still occurs technically, it may never be implemented discretely. This would be the case when, for instance, a multiplexer serves a number of IP network users; and then feeds directly into a router , which immediately reads the content of the entire link into its routing processor; and then does the demultiplexing in memory from where it will be converted directly into IP sections. Often,

1159-656: A single output line. The selection is directed by a separate set of digital inputs known as select lines. A multiplexer of 2 n {\displaystyle 2^{n}} inputs has n {\displaystyle n} select lines, which are used to select which input line to send to the output. A multiplexer makes it possible for several input signals to share one device or resource, for example, one analog-to-digital converter or one communications transmission medium , instead of having one device per input signal. Multiplexers can also be used to implement Boolean functions of multiple variables. Conversely,

1220-413: A specific source, be it a memory chip or a hardware peripheral. A computer uses multiplexers to control the data and address buses, allowing the processor to select data from multiple data sources In digital communications, multiplexers allow several connections over a single channel, by connecting the multiplexer's single output to the demultiplexer's single input (Time-Division Multiplexing). The image to

1281-798: A substantially improved performance over its metal-gate counterpart. In less than 10 years, the silicon gate MOS transistor replaced bipolar circuits as the main vehicle for complex digital ICs. There are a couple of drawbacks associated with PMOS: The electron holes that are the charge (current) carriers in PMOS transistors have lower mobility than the electrons that are the charge carriers in NMOS transistors (a ratio of approximately 2.5), furthermore PMOS circuits do not interface easily with low voltage positive logic such as DTL-logic and TTL-logic (the 7400-series). However, PMOS transistors are relatively easy to make and were therefore developed first — ionic contamination of

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1342-523: A transistor with lower parasitic capacitances that could be manufactured as part of an IC (and not only as a discrete component ). This new type of pMOS transistor was 3–5 times as fast (per watt) as the aluminum-gate pMOS transistor, and it needed less area, had much lower leakage and higher reliability. The same year, Faggin also built the first IC using the new transistor type, the Fairchild 3708 (8-bit analog multiplexer with decoder ), which demonstrated

1403-399: Is enhancement mode so that it can act as a logic switch. Since suitable resistors were hard to make, the logic gates used saturated loads; that is, to make the one type of transistor act as a load resistor, the transistor had to be turned always on by tying its gate to the power supply (the more negative rail for PMOS logic , or the more positive rail for NMOS logic ). Since the current in

1464-498: Is always true, the demultiplexer acts as a binary decoder . This means that any function of the selection bits can be constructed by logically OR-ing the correct set of outputs. If X is the input and S is the selector, and A and B are the outputs: A = ( X ∧ ¬ S ) {\displaystyle A=(X\wedge \neg S)} B = ( X ∧ S ) {\displaystyle B=(X\wedge S)} For 7400 series part numbers in

1525-420: Is due only to the transient power draw when the output state is changed and the p- and n-transistors thereby briefly conduct at the same time. However, this is a simplified view, and a more complete picture has to also include the fact that even purely static CMOS circuits have significant leakage in modern tiny geometries, as well as the fact that modern CMOS chips often contain dynamic and/or domino logic with

1586-423: Is equivalent to an 8-to-1. For 7400 series part numbers in the following table, "x" is the logic family. Demultiplexers take one data input and a number of selection inputs, and they have several outputs. They forward the data input to one of the outputs depending on the values of the selection inputs. Demultiplexers are sometimes convenient for designing general-purpose logic because if the demultiplexer's input

1647-402: Is the number of inputs. For example, 9 to 16 inputs would require no fewer than 4 selector pins and 17 to 32 inputs would require no fewer than 5 selector pins. The binary value expressed on these selector pins determines the selected input pin. A 2-to-1 multiplexer has a Boolean equation where A {\displaystyle A} and B {\displaystyle B} are

1708-552: The Intel 80386 and certain microcontrollers . A few years later, in the late 1980s, BiCMOS was introduced for high-performance microprocessors as well as for high speed analog circuits . Today, most digital circuits, including the ubiquitous 7400 series , are manufactured using various CMOS processes with a range of different topologies employed. This means that, in order to enhance speed and save die area (transistors and wiring), high speed CMOS designs often employ other elements than just

1769-556: The bipolar 7400 series and the CMOS 4000 series , although designs with several second source manufacturers often achieved something of a de facto standard component status. One example of this is the NMOS 8255 PIO design, originally intended as an 8085 peripheral chip, that has been used in Z80 and x86 embedded systems and many other contexts for several decades. Modern low power versions are available as CMOS or BiCMOS implementations, similar to

1830-428: The complementary static gates and the transmission gates of typical slow low-power CMOS circuits (the only CMOS type during the 1960s and 1970s). These methods use significant amounts of dynamic circuitry in order to construct the larger building blocks on the chip, such as latches, decoders, multiplexers, and so on, and evolved from the various dynamic methodologies developed for NMOS and PMOS circuits during

1891-399: The de facto standard from the mid-1970s to early 2000s) was an important first step in order to reduce this handicap. This new self-aligned silicon-gate transistor was introduced by Federico Faggin at Fairchild Semiconductor in early 1968; it was a refinement (and the first working implementation) of ideas and work by John C. Sarace, Tom Klein and Robert W. Bower (around 1966–67) for

Depletion-load NMOS logic - Misplaced Pages Continue

1952-408: The manufacturing process demanded additional manufacturing steps compared to the simpler enhancement-load circuits; this is because depletion-load devices are formed by increasing the amount of dopant in the load transistors channel region, in order to adjust their threshold voltage . This is normally performed using ion implantation . Although the CMOS process replaced most NMOS designs during

2013-496: The 1960s. The first IBM NMOS product was a memory chip with 1   kb data and 50–100 ns access time , which entered large-scale manufacturing in the early 1970s. This led to MOS semiconductor memory replacing earlier bipolar and ferrite-core memory technologies in the 1970s. In the late 1960s, bipolar junction transistors were faster than (p-channel) MOS transistors then used and were more reliable, but they also consumed much more power, required more area, and demanded

2074-423: The 1970s. Compared to static CMOS, all variants of NMOS (and PMOS) are relatively power hungry in steady state. This is because they rely on load transistors working as resistors , where the quiescent current determines the maximum possible load at the output as well as the speed of the gate (i.e. with other factors constant). This contrasts to the power consumption characteristics of static CMOS circuits, which

2135-402: The 1970s; the process supported both enhancement-mode and depletion-mode transistors, and typical logic circuits used enhancement-mode devices as pull-down switches and depletion-mode devices as loads, or pull-ups. Logic families built in older processes that did not support depletion-mode transistors were retrospectively referred to as enhancement-load logic, or as saturated-load logic, since

2196-588: The 1971 Intel 4004 used enhancement-load silicon-gate PMOS logic , and the 1976 Zilog Z80 used depletion-load silicon-gate NMOS. The original two types of MOSFET logic gates, PMOS and NMOS, were developed by Frosch and Derick in 1957 at Bell Labs. In 1963, both depletion- and enhancement-mode MOSFETs were described by Steve R. Hofstein and Fred P. Heiman at RCA Laboratories . In 1966, T. P. Brody and H. E. Kunig at Westinghouse Electric fabricated enhancement- and depletion-mode indium arsenide (InAs) MOS thin-film transistors (TFTs). In 2022,

2257-526: The 1980s, some depletion-load NMOS designs are still produced, typically in parallel with newer CMOS counterparts. One example of this is the Z84015 and Z84C15. The original two types of MOSFET logic gates, PMOS and NMOS , were developed by Frosch and Derick in 1957 at Bell Labs. Following this research, Atalla and Kahng proposed demonstrated a working MOS device with their Bell Labs team in 1960. Their team included E. E. LaBate and E. I. Povilonis who fabricated

2318-442: The 7400-series. Intel's own depletion-load NMOS process was known as HMOS , for High density, short channel MOS . The first version was introduced in late 1976 and first used for their static RAM products, it was soon being used for faster and/or less power hungry versions of the 8085, 8086, and other chips. HMOS continued to be improved and went through four distinct generations. According to Intel, HMOS II (1979) provided twice

2379-531: The area-economy considerably although the effect on the speed is complex. Processors built with depletion-load NMOS circuitry include the 6800 (in later versions), the 6502 , Signetics 2650 , 8085 , 6809 , 8086 , Z8000 , NS32016 , and many others (whether or not the HMOS processors below are included, as special cases). A large number of support and peripheral ICs were also implemented using (often static) depletion-load based circuitry. However, there were never any standardized logic families in NMOS, such as

2440-439: The decimal value of the binary control inputs at which that input is let through. Larger Multiplexers can be constructed by using smaller multiplexers by chaining them together. For example, an 8-to-1 multiplexer can be made with two 4-to-1 and one 2-to-1 multiplexers. The two 4-to-1 multiplexer outputs are fed into the 2-to-1 with the selector pins on the 4-to-1's put in parallel giving a total number of selector inputs to 3, which

2501-404: The density and four times the speed/power product over other typical contemporary depletion-load NMOS processes. This version was widely licensed by 3rd parties, including (among others) Motorola who used it for their Motorola 68000 , and Commodore Semiconductor Group , who used it for their MOS Technology 8502 die-shrunk MOS 6502 . The original HMOS process, later referred to as HMOS I, had

Depletion-load NMOS logic - Misplaced Pages Continue

2562-462: The desired output for each combination of the selector inputs. Multiplexers have found application in unconventional stochastic computing (SC), particularly in facilitating arithmetic addition. In this paradigm, data is represented as a probability bitstream where the number of '1' bits signifies the magnitude of a value. Thus, the function of a 2-to-1 multiplexer can be conceptualized as a probability function denoted as: y = P (

2623-524: The device; M. O. Thurston, L. A. D’Asaro, and J. R. Ligenza who developed the diffusion processes, and H. K. Gummel and R. Lindner who characterized the device. However, the NMOS devices were impractical, and only the PMOS type were practical working devices. In 1965, Chih-Tang Sah , Otto Leistiko and A.S. Grove at Fairchild Semiconductor fabricated several NMOS devices with channel lengths between 8   μm and 65   μm. Dale L. Critchlow and Robert H. Dennard at IBM also fabricated NMOS devices in

2684-495: The enhancement-mode transistors were typically connected with gate to the V DD supply and operated in the saturation region (sometimes the gates are biased to a higher V GG voltage and operated in the linear region, for a better power–delay product (PDP), but the loads then take more area). Alternatively, rather than static logic gates, dynamic logic such as four-phase logic was sometimes used in processes that did not have depletion-mode transistors available. For example,

2745-412: The first dual-mode organic transistor that behaves in both depletion mode and enhancement mode was reported by a team at University of California-Santa Barbara. Multiplexer In electronics , a multiplexer (or mux ; spelled sometimes as multiplexor ), also known as a data selector , is a device that selects between several analog or digital input signals and forwards the selected input to

2806-486: The following table, "x" is the logic family. Bi-directional multiplexers are built using analog switches or transmission gates controlled by the select pins. This allows the roles of input and output to be swapped so that a bi-directional multiplexer can function both as a demultiplexer and multiplexer. Multiplexers can also be used as programmable logic devices , to implement Boolean functions. Any Boolean function of n variables and one result can be implemented with

2867-429: The gate junction would forward bias if the gate were taken more than a little from source toward drain voltage. Such devices are used in gallium arsenide and germanium chips, where it is difficult to make an oxide insulator. Some sources say "depletion type" and "enhancement type" for the device types as described in this article as "depletion mode" and "enhancement mode", and apply the "mode" terms for which direction

2928-415: The gate oxide from etching chemicals and other sources can very easily prevent (the electron based) NMOS transistors from switching off, while the effect in (the electron-hole based) PMOS transistors is much less severe. Fabrication of NMOS transistors therefore has to be many times cleaner than bipolar processing in order to produce working devices. Early work on NMOS integrated circuit (IC) technology

2989-401: The gate–source voltage differs from zero. Moving the gate voltage toward the drain voltage "enhances" the conduction in the channel, so this defines the enhancement mode of operation, while moving the gate away from the drain depletes the channel, so this defines depletion mode. Depletion-load NMOS logic refers to the logic family that became dominant in silicon VLSI in the latter half of

3050-592: The highest performing versions of the chip had access times of less than 100ns, taking MOS memories close to the speed of bipolar RAMs for the first time. Depletion-load NMOS processes were also used by several other manufacturers to produce many incarnations of popular 8-bit, 16-bit, and 32-bit CPUs. Similarly to early PMOS and NMOS CPU designs using enhancement mode MOSFETs as loads, depletion-load nMOS designs typically employed various types of dynamic logic (rather than just static gates) or pass transistors used as dynamic clocked latches . These techniques can enhance

3111-474: The industry’s first 4-kbit IC ROM . Motorola eventually served as a second source for these products and so became one of the first commercial semiconductor vendors to master the NMOS process, thanks to Hewlett-Packard. A while later, the startup company Intel announced a 1-kbit pMOS DRAM, called 1102 , developed as a custom product for Honeywell (an attempt to replace magnetic core memory in their mainframe computers ). HP’s calculator engineers, who wanted

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3172-434: The load transistors could be adjusted reliably. At Intel, depletion load was introduced in 1974 by Federico Faggin, an ex-Fairchild engineer and later the founder of Zilog . Depletion-load was first employed for a redesign of one of Intel's most important products at the time, a +5V-only 1Kbit NMOS SRAM called the 2102 (using more than 6000 transistors). The result of this redesign was the significantly faster 2102A , where

3233-480: The polarities are reversed. The mode can be determined by the sign of the threshold voltage (gate voltage relative to source voltage at the point where an inversion layer just forms in the channel): for an N-type FET, enhancement-mode devices have positive thresholds, and depletion-mode devices have negative thresholds; for a P-type FET, enhancement-mode have negative, and depletion-mode have positive. Junction field-effect transistors ( JFETs ) are depletion-mode, since

3294-422: The pull-up is the same kind of transistor as is used for logic switches. As the output voltage approaches a value less than Vdd , it gradually switches itself off. This slows the 0 to 1 transition, resulting in a slower circuit. Depletion-load processes replace this transistor with a depletion-mode NMOS at a constant gate bias, with the gate tied directly to the source. This alternative type of transistor acts as

3355-580: The pull-up. Both (enhancement-mode) saturated-load and depletion-mode pull-up transistors use greatest power when the output is stable at 0 , so this loss is considerable. Because the strength of a depletion-mode transistor falls off less on the approach to 1 , they may reach 1 faster despite starting slower, i.e. conducting less current at the beginning of the transition and at steady state. Depletion and enhancement modes In field-effect transistors (FETs), depletion mode and enhancement mode are two major transistor types, corresponding to whether

3416-445: The right demonstrates this benefit. In this case, the cost of implementing separate channels for each data source is higher than the cost and inconvenience of providing the multiplexing/demultiplexing functions. At the receiving end of the data link a complementary demultiplexer is usually required to break the single data stream back down into the original streams. In some cases, the far end system may have functionality greater than

3477-569: The selector wires are of digital value. In the case of a 2-to-1 multiplexer, a logic value of 0 would connect I 0 {\displaystyle I_{0}} to the output while a logic value of 1 would connect I 1 {\displaystyle I_{1}} to the output. In larger multiplexers, the number of selector pins is equal to ⌈ log 2 ⁡ ( n ) ⌉ {\displaystyle \left\lceil \log _{2}(n)\right\rceil } where n {\displaystyle n}

3538-471: The systems worked as the layout changed. HMOS, HMOS II, HMOS III, and HMOS IV were together used for many different kinds of processors; the 8085 , 8048 , 8051 , 8086 , 80186 , 80286 , and many others, but also for several generations of the same basic design, see datasheets . In the mid-1980s, faster CMOS variants, using similar HMOS process technology, such as Intel's CHMOS I, II, III, IV, etc. started to supplant n-channel HMOS for applications such as

3599-537: The transistor is in an on state or an off state at zero gate–source voltage. Enhancement-mode MOSFETs (metal–oxide–semiconductor FETs) are the common switching elements in most integrated circuits. These devices are off at zero gate–source voltage. NMOS can be turned on by pulling the gate voltage higher than the source voltage, PMOS can be turned on by pulling the gate voltage lower than the source voltage. In most circuits, this means pulling an enhancement-mode MOSFET's gate voltage towards its drain voltage turns it on. In

3660-654: The two inputs, S 0 {\displaystyle S_{0}} is the selector input, and Z {\displaystyle Z} is the output: Which can be expressed as a truth table : Or, in simpler notation: These tables show that when S 0 = 0 {\displaystyle S_{0}=0} then Z = A {\displaystyle Z=A} but when S 0 = 1 {\displaystyle S_{0}=1} then Z = B {\displaystyle Z=B} . A straightforward realization of this 2-to-1 multiplexer would need 2 AND gates, an OR gate, and

3721-416: Was presented in a brief IBM paper at ISSCC in 1969. Hewlett-Packard then started to develop NMOS IC technology to get the promising speed and easy interfacing for its calculator business. Tom Haswell at HP eventually solved many problems by using purer raw materials (especially aluminum for interconnects) and by adding a bias voltage to make the gate threshold large enough; this back-gate bias remained

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