CMOS INVERTERS BASIC AND TUTORIALS

WHAT ARE CMOS INVERTERS? APPLICATION OF CMOS INVERTERS

As shown in Fig. 8.17(a), the CMOS inverter consists of an enhancement NMOS as the driving transistor, and a complementary enhancement PMOS load transistor. The driving transistor is off when Vin is low, and the load transistor is off when Vin is high. 

Thus, one of the two series transistors is always off (equivalently, drain current and power dissipation are zero) except during switching,when both transistors are momentarily on. The resulting low-power dissipation is an important CMOS advantage and makes it an attractive alternative in VLSI design. 

NMOS circuits are ratioed in the sense that the pull up never turns off, and VOL is determined by the inverter ratio. CMOS is ratioless in this sense, since VOL is always the negative rail. If one desires equal sourcing and sinking currents, however, the pull-up device must be wider than the pull-down device by the ratio of the electron-to-hole mobilities, typically about 2.5 to 1. 

This also gives a symmetrical voltage transfer curve, with the voltage at which Vin = VO having a value of VDD/2. This voltage is referred to as the inverter voltage Vinv.

The voltage transfer for the CMOS inverter is shown in Fig. 8.17(b). Note that the voltage transfer characteristic approaches that of the ideal logic inverter. These characteristics are best obtained with computer circuit simulation programs. 

As with the depletion load NMOS inverter, useful insights may be gained by performing an analytical solution. The analysis proceeds as previously described for the depletion load NMOS inverter. 

Note that the VTC of Fig. 8.17(b) has been divided into regions as in Fig. 8.15(a). In each region, the appropriate expressions for the load and driving transistor drain currents are equated so that VO can be computed for any given Vin. 

To find VI L and VI H, the condition that dVO/dVin = −1 at such critical voltages is applied to the drain current equation.Note that the drain current equations for the PMOS are the same as for NMOS, except for reverse voltage polarities for the PMOS.

HISTORY OF SOLID STATE ELECTRONICS BASICS

SOLID STATE ELECTRONICS BRIEF HISTORY

The crystal detectors used in early radios were the forerunners of modern solid-state devices. However, the era of solid-state electronics began with the invention of the transistor in 1947 at Bell Labs.

The inventors were Walter Brattain, John Bardeen, and William Shockley. PC (printed circuit) boards were introduced in 1947, the year the transistor was invented. Commercial manufacturing of transistors began in Allentown, Pennsylvania, in 1951.

The most important invention of the 1950s was the integrated circuit. On September 12, 1958, Jack Kilby, at Texas Instruments, made the first integrated circuit. This invention literally created the modern computer age and brought about sweeping changes in medicine, communication, manufacturing, and the entertainment industry.

Many billions of "chips"-as integrated circuits came to be called-have since been manufactured. The 1960s saw the space race begin and spurred work on miniaturization and computers.

The space race was the driving force behind the rapid changes in electronics that followed. The first successful "op-amp" was designed by Bob Widlar at Fairchild Semiconductor in 1965. Called the flA709, it was very successful but suffered from "latch-up" and other problems.

Later, the most popular op-amp ever, the 741, was taking shape at Fairchild. This opamp became the industry standard and influenced design of op-amps for years to come.

By 1971, a new company that had been formed by a group from Fairchild introduced the first microprocessor. The company was Intel and the product was the 4004 chip, which had the same processing power as the Eniac computer.

Later in the same year, Intel announced the first 8-bit processor, the 8008. In 1975, the first personal computer was introduced by Altair, and Popular Science magazine featured it on the cover of the January, 1975, issue.

The 1970s also saw the introduction of the pocket calculator and new developments in optical integrated circuits.

By the 1980s, half of all U.S. homes were using cable hookups instead of television antennas. The reliability, speed, and miniaturization of electronics continued throughout the 1980s, including automated testing and calibrating of PC boards. The computer became a part of instrumentation and the virtual instrument was created. Computers became a standard tool on the workbench.

The 1990s saw a widespread application of the Internet. In 1993, there were 130 websites, and now there are millions. Companies scrambled to establish a home page and many of the early developments of radio broadcasting had parallels with the Internet.

In 1995, the FCC allocated spectrum space for a new service called Digital Audio Radio Service. Digital television standards were adopted in 1996 by the FCC for the nation's next generation of broadcast television.

The 21st century dawned in January 2001. One of the major technology stories has been the continuous and explosive growth of the Internet. Internet usage in North America has increased by over 100% from 2000 to 2005.

The rest of the world experienced almost 200% growth during the same period. The processing speed of computers is increasing at a steady rate and data storage media capacity is increasing at an amazing pace. Carbon nanotubes are seen to be the next step forward for computer chips, eventually replacing transistor technology.