Editing Logic family (section)

==Complementary MOS (CMOS) logic==
{{main | CMOS}}

CMOS logic gates use complementary arrangements of enhancement-mode N-channel and P-channel [[field effect transistor]].  Since the initial devices used oxide-isolated metal gates, they were called '''[[CMOS]]''' (complementary metal–oxide–semiconductor logic).  In contrast to TTL, CMOS uses almost no power in the static state (that is, when inputs are not changing). A CMOS gate draws no current other than leakage when in a steady 1 or 0 state. When the gate switches states, current is drawn from the power supply to charge the capacitance at the output of the gate. This means that the current draw of CMOS devices increases with switching rate (controlled by clock speed, typically).

The first CMOS family of logic integrated circuits was introduced by [[RCA]] as ''CD4000 COS/MOS'', the  [[4000 series]], in 1968. Initially CMOS logic was slower than LS-TTL. However, because the logic thresholds of CMOS were proportional to the power supply voltage, CMOS devices were well-adapted to battery-operated systems with simple power supplies. CMOS gates can also tolerate much wider voltage ranges than TTL gates because the logic thresholds are (approximately) proportional to power supply voltage, and not the fixed levels required by bipolar circuits.

The required silicon area for implementing such digital CMOS functions has rapidly shrunk. [[Very-large-scale integration|VLSI technology]] incorporating millions of basic logic operations onto one chip, almost exclusively uses CMOS. The extremely small capacitance of the on-chip wiring caused an increase in performance by several orders of magnitude. On-chip clock rates as high as 4&nbsp;GHz have become common, approximately 1000 times faster than the technology by 1970.

===Lowering the power supply voltage===
{{main | LVCMOS}}

CMOS chips often work with a broader range of power supply voltages than other logic families. Early TTL ICs required a [[power supply]] [[voltage]] of 5V, but early CMOS could use 3 to 15V.<ref>{{cite book |title=RCA COS/MOS integrated circuits |publisher=RCA Corporation |date=1978 |oclc=4894263 |series=SSD-250A}}<!-- Might be in there if someone could look, page needed --></ref> Lowering the supply voltage reduces the charge stored on any capacitances and consequently reduces the energy required for a logic transition. Reduced energy implies less heat dissipation. The energy stored in a capacitance ''C'' and changing ''V'' volts is ½&nbsp;''CV''<sup>2</sup>. By lowering the power supply from 5V to 3.3V, switching power was reduced by almost 60 percent ([[CPU power dissipation|power dissipation]] is proportional to the square of the supply voltage). Many motherboards have a [[voltage regulator module]] to provide the even lower power supply voltages required by many CPUs.

===HC logic===

Because of the incompatibility of the CD4000 series of chips with the previous TTL family, a new standard emerged which combined the best of the TTL family with the advantages of the CD4000 family. It was known as the 74HC (which used anywhere from 3.3V to 5V power supplies (and used logic levels relative to the power supply)), and with devices that used 5V power supplies and TTL [[logic level]]s.

===The CMOS–TTL logic level problem===
{{Further|logic-level shifter}}
Interconnecting any two logic families often required special techniques such as additional [[pull-up resistor]]s, or purpose-built interface circuits, since the logic families may use different [[logic level|voltage levels]] to represent 1 and 0 states, and may have other interface requirements only met within the logic family.

TTL logic levels are different from those of CMOS – generally a TTL output does not rise high enough to be reliably recognized as a logic 1 by a CMOS input. This problem was solved by the invention of the 74HCT family of devices that uses CMOS technology but TTL input logic levels. These devices only work with a 5V power supply. They form a replacement for TTL, although HCT is slower than original TTL (HC logic has about the same speed as original TTL).

===Other CMOS families===

Other CMOS circuit families within [[integrated circuit]]s include [[cascode voltage switch logic]] (CVSL) and [[pass transistor logic]] (PTL) of various sorts.  These are generally used "on-chip" and are not delivered as building-block medium-scale or small-scale integrated circuits.<ref>{{cite book |last1=Baker |first1=R. Jacob |url=https://books.google.com/books?id=N0XgLh2d2pkC |title=CMOS Circuit Design, Layout, and Simulation |volume=1 |publisher=Wiley |year=2008 |pages=369–370 |isbn=978-0470229415 |accessdate=2021-11-17 }}</ref><ref>{{cite book |last1=Segura |first1=Jaume |last2=Hawkins |first2=Charles F. |url=https://books.google.com/books?id=Vl8naJHBTDIC |title=CMOS Electronics How It Works, How It Fails |publisher=Wiley |date=2004-03-26 |page=132 |isbn=978-0471476696 |accessdate=2021-11-17 }}</ref>