Posts Tagged cmos

HOW CMOS WORKS: MOSFETS, JFETS, IGFETS AND MORE

CMOS opened the door for many if not most of the properties needed for today’s highly integrated circuits and low power portable and mobile devices. This really couldn’t happen until the speeds and current drive capabilities of CMOS caught up to the other technologies, but catch up they did.

Nowadays CMOS Small Scale Integration (SSI) logic families, I.E. the gates used in external logic, offer very fast speeds and high current drive capability as well as supporting the low voltages found in modern designs. Likewise the Very Large Scale Integration (VLSI) designs, or Very Very Large Scale if you like counting the letter V when talking, are possible due to low power dissipation as well as other factors.

HOW CMOS IS DESIGNED

CMOS, which means Complementary Metal Oxide Semiconductor, is based on combining two polarities of MOSFETS; Metal Oxide Semiconductor Field Effect Transistors.

BJTRegular transistors, known as Bipolar Junction Transistors (BJT) meaning that they are made from junctions that have a positive and a negative (PN) junction utilize current as the input and create gain by controlling output current. As all of these current flows add up it means that at the end of the day there is a lot of current flowing which results in power being dissipated which ultimately results in heat.

JFETThe Junction Field Effect Transistor (JFET) utilizes voltage instead of current on its Gate input, somewhat like the Base on a Bipolar Transistor, to control the output voltage. Since the Gate is not insulated from the other terminals, known as the Source and Drain, there is a leakage current in JFETs that would not be present if the Gate was insulated from the Source and Drain.
Enter the Insulated Gate FET (IGFET) which is the basis for most of the transistor devices found on large scale integrated chips today. Looking at the diagram, the MOSFETs all show a distinct space between the Gate and the rest of the structure. The other two pins are the Source and the Drain.

Read more at Hackaday.com

 

 

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GATES TO FPGAS: TTL ELECTRICAL PROPERTIES

On the path to exploring complex logic, let’s discuss the electrical properties that digital logic signals are comprised of. While there are many types of digital signals, here we are talking about the more common voltage based single-ended signals and not the dual-conductor based differential signals.

Simulated "Real Life"
Single-ended Logic Signal

I think of most logic as being in one of two major divisions as far as the technology used for today’s logic: Bipolar and CMOS. Bipolar is characterized by use of (non-insulated gate) transistors and most often associated with Transistor Transistor Logic (TTL) based logic levels. As CMOS technology came of age and got faster and became able to drive higher currents it began to augment or offer an alternative to bipolar logic families. This is especially true as power supply voltages dropped and the need for low power increased

Read more at Hackaday.com

 

 

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