VLSI - 1

Without doubt, VLSI is top branch of ECE which fascinates many graduates and also a hot cake, henceforth making it a very competitive branch to get into even in your Mtech.

Roughly one can divide VLSI into 3 specializations:

Analog VLSI
Digital VLSI
Device Electronics

Analog VLSI  --- is something that really fascinates many VLSI students but often, doesn't become a career option for many of those bright students. It is much more than the coding stuff. Analog needs your thinking cap to be on always. It needs understanding of device physics too to a reasonable extent.

Any chip that gets taped out has all blocks of analog, digital. Band gap ckts, Reference current sources, IO components, PLLs, Amplifiers, filters, transmitters, receivers and many blocks are all analog in nature.

Most of the digital stuff are coded and even the interface circuits that is A/D convertors, sensors, and D/A convertors are all analog blocks !!!

The real world is analog in nature and any advancements we talk about DSP, can be appreciated only if u have proper interface circuits to convert the analog signal to digital and do DSP and convert it back to analog again.

Difference between fluorescence and phosphorescence

When electron beam hits phosphorus coated screen, some of the energy of these electrons in dissipated as heat and rest is transferred to electrons of phosphorus which makes them jump to higher energy levels. As we know that higher energy state is unstable and when electron comes to its original state energy is emitted in the form of light(color of light depend upon level from which electrons is returning).

In Ph, some energy levels are less stable than others so electrons in this state returns more rapidly than others.

 Hence energy(in the form of light) emitted when these unstable electron return from higher state to its original state while electrons are bombarded on it is called fluorescence.

While the  energy emitted when stable electrons return from higher energy levels to its original energy level once electron beam excitation is removed is called phosphorescence.

most of the light emitted in typical Ph is phosphorescence.

Persistence : It is defined as the time from removal of excitation of electron beam to the time when the phosphorescence has decayed to 10% of initial light output. Typically it is between 10-60 microsecond.