What is Cmos: Definition and 78 Discussions

Complementary metal–oxide–semiconductor (CMOS, pronounced "see-moss"), also known as complementary-symmetry metal–oxide–semiconductor (COS-MOS), 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 (including CMOS BIOS), and other digital logic circuits. CMOS technology is also used for analog circuits such as image sensors (CMOS sensors), data converters, RF circuits (RF CMOS), and highly integrated transceivers for many types of communication.
Mohamed M. Atalla and Dawon Kahng invented the MOSFET at Bell Labs in 1959, and then demonstrated the PMOS (p-type MOS) and NMOS (n-type MOS) fabrication processes in 1960. These processes were later combined and adapted into the complementary MOS (CMOS) process by Chih-Tang Sah and Frank Wanlass at Fairchild Semiconductor in 1963. RCA commercialized the technology with the trademark "COS-MOS" in the late 1960s, forcing other manufacturers to find another name, leading to "CMOS" becoming the standard name for the technology by the early 1970s. CMOS eventually overtook NMOS as the dominant MOSFET fabrication process for very large-scale integration (VLSI) chips in the 1980s, while also replacing earlier transistor–transistor logic (TTL) technology. CMOS has since remained the standard fabrication process for MOSFET semiconductor devices in VLSI chips. As of 2011, 99% of IC chips, including most digital, analog and mixed-signal ICs, are fabricated using CMOS technology.Two important characteristics of CMOS devices are high noise immunity and low static power consumption.
Since one transistor of the MOSFET pair is always off, the series combination draws significant power only momentarily during switching between on and off states. Consequently, CMOS devices do not produce as much waste heat as other forms of logic, like NMOS logic or transistor–transistor logic (TTL), which normally have some standing current even when not changing state. These characteristics allow CMOS to integrate a high density of logic functions on a chip. It was primarily for this reason that CMOS became the most widely used technology to be implemented in VLSI chips.
The phrase "metal–oxide–semiconductor" is a reference to the physical structure of MOS field-effect transistors, having a metal gate electrode placed on top of an oxide insulator, which in turn is on top of a semiconductor material. Aluminium was once used but now the material is polysilicon. Other metal gates have made a comeback with the advent of high-κ dielectric materials in the CMOS process, as announced by IBM and Intel for the 45 nanometer node and smaller sizes.

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  1. E

    Engineering Negative PSRR of the Two-Stage Op Amp

    From page 4-9 of this lecture note https://pallen.ece.gatech.edu/Academic/ECE_6412/Spring_2004/L180-PSRR-2UP.pdf, it gives example on how to model a Two-Stage Op Amp to find the PSRR- when VBias is connecting to ground as oppose to when VBias is connecting to Vss. One thing I don't understand is...
  2. Joshy

    Engineering Equivalent resistance of an envelope peak detector (RF CMOS)

    Full problem: I don't normally think about circuits like these in terms of energy (Joules) so I was very much confused. What I did was find where the simplified expressions intercepts with each other to get the voltage. I scanned in my work although this text is a walk through of what I did...
  3. M

    Final semester project ideas using CMOS VLSI?

    Guys ! I need your help in choosing a better project for my last semester .Can anyone suggest me projects based on CMOS VLSI Technology.?
  4. jisbon

    Engineering Constructing a CMOS circuit

    As attached below, I have drawn the step down and up diagram. However comparing to the answer, it seems to be way too off. Any idea why? Answer: Is there something wrong with my step down/step up circuit?
  5. jisbon

    Engineering Constructing a CMOS AND circuit with MOSFETs

    Hi all :) So I constructed this based on a video tutorial, p, and n MOS, and was wondering if it was correct before I combine them. Also, it looks very different from what the proposed answer is. Since the equation is z=ab, The pull-down diagram looks like this: and the pull-up is z= a'+b'...
  6. J

    Thermal radiation in CMOS transistors

    Inside a CPU, when applying voltage to the gates of the CMOS transistor(high input), are the gate ore another components of a transistor will generate thermal radiation which will be absorbed by the neighboring transistor?
  7. J

    Frequency divider using CMOS

    I made a table using excel as: D is output. Like this I get Output frequency is same as input frequency. But I'm not sure if this is correct. PS: I'm aware I'm posting many questions, but I got interview exams coming up in August. Companies are going to come to university for recruitment and...
  8. J

    Voltage divider rule for CMOS in 0-state and leakage current

    I use the voltage divider rule as output voltage = Voltage across R1 = 5 * ( 0.5 / (0.5 + 20) ) This comes as 0.122 V I'm not sure why they've mentioned I leakage and does 0-state have any impact on answer.
  9. PainterGuy

    Can a CMOS BIOS Battery Failure Leave Your Computer Useless?

    Hi, I was reading about CMOS BIOS which was once used in computers to store BIOS settings is a CMOS RAM using a battery backup. This article, https://www.makeuseof.com/tag/why-does-my-motherboard-have-a-battery/, says, "If the battery fails on an older computer that stores its BIOS settings...
  10. D

    Finding the CMOS transistor width ratio

    Homework Statement Calculate the ration of ##w_p/w_n## if n and p transistors in CMOS inverter necessary for the least delay time ##t_p## if the circuit is used in a chain of circuits. a) What is ##w_p## in that circuit if you're given : b) Calculate the maximum short circuit current if...
  11. T

    Explore New Business Fields for Light Sensitive Sensors

    Hey :) I am currently doing a project on university in cooperation with CERN where I have to find new business fields for light sensitive sensors (CMOS) which every camera contains. The special feature is the radiation hardness. So you can use it for example for detecting x-rays or you can use...
  12. O

    Threshold voltage calculation of a CMOS gate

    Hello all, I want to know a suitable way to calculate VTL and VTH of a gate having the gate schematic and constituent transistors SPICE model (NMOS/PMOS models). Is there an easier than doing hand calculations ?
  13. B

    Designing Photonic Integrated Circuit: Photodiode to CMOS

    I am now trying to design a photonic integrated circuit which will be used to replace the global interconnect layer of a LSI. I need to somehow take the output of a photodiode w/o TIA (10G signal perhaps) and then transmit that signal to other layer of the LSI by TSV or something. Assume a...
  14. STEMucator

    Implementing Logic Using Conventional CMOS Logic

    Homework Statement This question has several parts, and I'm confused about some of them. Consider ##Z = \overline{(A + B \bar{C})D + E \bar{F}}##. Assume primary and inverted inputs are available. A) Implement the function in conventional CMOS logic style such that only 4 transistors are...
  15. T

    Logic outputs to logic inputs of devices with different Vcc

    Hello engineers! :)I have a question bothering me i quite can't figure out. I have a Priority encoder: http://www.digikey.com/product-search/en?vendor=0&keywords=ls148d&stock=1 datasheet: http://www.ti.com/lit/ds/symlink/sn74ls148.pdfAnd this RF-Switch...
  16. N

    CMOS to Microstrip Impedance Matching

    I need to somehow take the output of a CMOS IC and transmit that signal over a 50 Ohm Microstrip line. The output impedance of the CMOS IC is about 15 megaohms. I see a lot of examples for going from 75 ohms to 50 ohms or similar but nothing on something of this magnitude. Any ideas? CMOS...
  17. O

    Characteristics of CMOS gate

    Homework Statement 1)Determine the min acceptable values for VIH and VOH using VCC = 4.5 V and output current of 20 µA. 2)Determine the maximum acceptable values for VOL and VIL under the same test conditions. 3)Compute the noise margins. Homework Equations i=v/R The Attempt at a Solution...
  18. J

    CMOS Sensor with external reset control

    Hi I've been searching for a CMOS or CCD sensor with raw analog output and external reset/transfer control but has not been able to find this. Doesn't have to be great resolution. Anyone knows if there is a sensor like this on the market today? Best Johan
  19. A

    "Black sun" effect in CMOS sensors

    Hi, I would like to understand the reason for the "Black sun" effect that occurs in CMOS cameras (very bright spots appear as dark). Thanks, ALex
  20. D

    CMOS Current in triode region equation

    Homework Statement Q. I was given a equation for PMOS and NMOS drain current in triode region but I am having some confusion regarding equation please do help. I think drain to source current in PMOS should be negative but in equation value will come out to be positive if I keep V(gs) ,V(ds)...
  21. reddvoid

    Spikes in CMOS Inverter transients

    I am simulating cmos inverter in CADENCE I am getting a sharp spike when output is going from low to high and spike became more amplified like when i made rise time and fall time of input rectangular pulse signal very low . . .can somebody explain why this happening ?
  22. A

    MHB CMOS inverters

    Hello. Can someone explain to me what does $V_i=L$ and $V_i=H$ mean in CMOS inverters?
  23. M

    Understanding CMOS Inverter Behavior: V_i=L and V_i=H Explained

    Hello. Can someone explain to me what does ##V_i=L## and ##V_i=H## mean in CMOS inverters?
  24. vead

    Optimizing Power, Speed, and Size: Tips for CMOS Circuit Design"

    when designer design new circuit, they think what's the requirement step I 1)power dissipation should be less 2)raise time and fall time should be less 3)propagation delay time should be less 4)size should be small as possible step II 1) how can we reduce power dissipation in cmos...
  25. A

    Output states of a CMOS gate

    Please help me with the question in the picture about pull-up and pull-down networks.
  26. L

    SPDT switches in CMOS processes.

    Hi guys, Recently I had to design a SPDT switch for a project, which I was able to design using the trivial circuit with 2 transmission gates and 1 MOS inverter, like this: http://www.semicon.toshiba.co.jp/eng/product/new_products/logic/1326183_37648.html I think that this circuit is not...
  27. W

    Efficient CMOS Comparator Circuit for PWM Experiments with Sawtooth Generator

    I have been experimenting with PWM circuits and I came across this CMOS comparator that seems to work well with the sawtooth generator I am using. I feed a sawtooth wave to the gate of the PMOS M3 transistor and the reference voltage I am comparing to Vin the PMOS M4. I noticed that the...
  28. D

    Engineering CMOS Circuit JSIM: Solving & Coding Help

    Homework Statement uploaded Homework Equations uploaded The Attempt at a Solution I have Jsim installed and working and have the circuit correctly done. I however don't understand how the coding works in Jsim. I essentially need the equivalent circuit in Jsim code. I need help...
  29. K

    Delay through CMOS Inverter.

    When calculating delay, like the fall time delay of the output, through an inverter with rc model of the transistors (assuming Cmos inverter) why do we neglect the short circuit current through the device and what are the assumptions. Can anyone explain this?
  30. S

    Engineering PSPICE - simulation of CMOS astable circuit

    Homework Statement I'm trying to simulate the following circuit in OrCAD PSPICE. Homework Equations The Attempt at a Solution * 8.20 Vdd 1 0 5V MP1 3 2 1 1 PMOD MN1 3 2 0 0 NMOD MP2 4 3 1 1 PMOD MN2 4 3 0 0 NMOD R1 3 2 1000 C1 2 4 1uF .MODEL...
  31. T

    CMOS Regions of Operation Problem

    In the attached photo, I found M2 to be triode region b/c the drain and drain source voltage is 0 which will always be less than the output voltage. However, I am have troubles finding M1's region of operation, VDS >= VGS - VTH. Vout - Vbias >= Vdd - Vbias - VTH **Vbias = 0.8 V...
  32. perplexabot

    Max Current in CMOS Inverter with Given Parameters

    Hi all, I have gave this question a lot of thought but can't seem to get anywhere. Any help will be much appreciated. Homework Statement For a digital logic inverter for which k'n = 120 uA/V^2, k'p = 60 uA/V^2, Vtn = |Vtp| = .7V, VDD = 3V, Ln = Lp = .8 um, Wn = 1.2 um and Wp = 2.4 um...
  33. perplexabot

    How can I calculate Vout for a CMOS inverter?

    Hi all. I don't know if I have given this enough thought but I will ask anyway. I know that a CMOS is an inverter, so for input High you will get output Low, and for input Low you will get output High. I am trying to find this out mathematically (or even just logically) but I can't seem to do...
  34. A

    Mastering CMOS Circuit Drawing: Get Expert Feedback on Your XOR Gate Design

    I understand how to draw a CMOS circuit but I am not so confident if I do it right. I need someone to check if I draw them right. As for the second one which is a XOR gate, I am not sure at all on how to draw it since there are both the 0 and 1 inputs in the circuit.
  35. Z

    Comparing TTL and CMOS gates.

    Homework Statement We just did an experiment on the input and output characteristics of TTL and CMOS NAND gates. We recorded the following data for each of the two gates. 1) Input Threshold Voltage 2) Input Current(for input logic 1 and 0) 3) Output Voltage(for output logic 1 and 0) 4)...
  36. N

    CMOS vs. BJT: Which is Better for Power Management Circuit Design?

    I'm a bit of a noob on all of this, but can anyone help me (or point to a great reference resource) on pro's and con's of each in designing a power management circuit? Specifically, I'm looking for what kinds of voltage and frequency applications each manufacturing process is used nowadays...
  37. N

    Recognizing Gate, Source & Drain for NMOS & PMOS

    Homework Statement I saw this image in the internet. I want to learn how to recognize the gate, source and drain for NMOS and PMOS. The Attempt at a Solution I don't know if I am correct or not. M8 ( with an arrow coming out ) is NMOS. M7B (with an arrow going in) is a PMOS...
  38. N

    CMOS Resistance: Drawing NAND & Solutions

    Homework Statement I drew a NAND in the picture. The Attempt at a Solution I know when A and B are both high ( value 1), resistance will be Rn + Rn because those 2 NMOS will be turned on and resistance will added up since they are in series. Also when A and B are both...
  39. N

    Constructing Complex CMOS Gates | Understanding NAND and NOR Logic

    Homework Statement It given the expression . how to construct the complex CMOS gate by looking at the expression. Homework Equations The Attempt at a Solution This solution is given as well. I don't understand how he construct it. I know NAND is fromed by two PMOS in...
  40. N

    CMOS gate for the logic function

    Hello. One of my friends told me that the logic function for (A.or.B).and.(C.or.D) is From a book, I know the P1, P2 , N1, N2 form a NAND. The same for P3, P4, N3, N4. And P5, P6, N5, N6 form a NOR. My question is, is this circuit the same as (A.or.B).and.(C.or.D) ? Thank you
  41. S

    Engineering Basic Cmos circuit question

    Homework Statement The following question: when Vw is VDD=2.5V, what are the output voltages for VX,VY and VZ Homework Equations N/AThe Attempt at a Solution this is what i though since the p-mos is ON, VX=VW-|Vtp| now the voltage at VY=VX-Vtn =VW-|Vtp|-Vtn and the answer is wrong, can some...
  42. S

    PSPICE error message when simulating CMOS inverter circuit.

    Hi. I receive an error message once simulating in PSPICE. I have attached a file that explains the problem in details. Will be glad to know the source of the problem. Thanks! :redface:
  43. I

    CMOS inverter DC analysis

    Hello, I have a question about how to analyze the CMOS inverter (this circuit: http://www.cs.umass.edu/~weems/CmpSci635A/Lecture2/image10.gif [Broken]). Just to clarify, the input voltage is connected to both gates, and the PMOS on top has its source connected to Vdd. The NMOS on the bottom...
  44. E

    Designing CMOS Logic XOR Gate & 2:1 Multiplexer

    I am designing cmos logic xor gate and 2:1 multiplexer. In my design i am using 8 pmos and 8 nmos for 2:1 mux and 6 pmos and 6 nmos for xor gate. I am using pmos and nmos to implement complement A, means that i am not using complement directly into the circuit. So , i want to know that is it...
  45. S

    Engineering CMOS inverter circuit, spike in simulation

    Hello, I am hoping someone can give me a little bit of help. I have been simulating a CMOS inverter circuit. When I add in a pulse source at the input, and simulate it, I get an output which has a bit of a spikle on the transition. I am hoping someone can help my understand why this is...
  46. C

    Interview Q - CMOS inverter

    Heres an interview question which I am having trouble with: Consider a CMOS inverter. Replace the NMOS in it with a PMOS. How would the VTC curve look like? I was told that one PMOS would always be in saturation. Since the source voltage of the lower PMOS is tied to Vout, how can we...
  47. S

    Can a CMOS sensor be used as a Geiger nounter

    Can a CMOS sensor be used as a Geiger counter To help the folks in Japan protect themselves from contaminated food and to get some assurance of the safety of their homes, we are putting together a team to evaluate the feasibility of writing an iPhone/Android application that would use the CMOS...
  48. J

    5V TTL to 12V Cmos conversion

    Hi, new to these forums and glad I found them! I am working on a project that requires conversion of fairly hi-speed signals (10us pulses) from 5V to 12V. The usual open collector with a pull up is much too slow getting from 0 to 12V. I really need the ramp to happen between .05us to 1us...
  49. L

    Exploring the Logic Behind CMOS Voltage: 3.3V

    Why is the CMOS logic voltage exactly 3.3V, why not 3V or 3.5V?
  50. S

    Rocket Camera, CMOS vs. CCD

    I'm looking for a small camera to use in my rocket. It's about a 7' rocket, 4" diameter and 3" long viewing window. I've heard that the choices are either cmos or ccd but I don't know the difference between the two. I'm only looking to spend up to $100 (really looking in the $50 range). Any...