The written test is separate for hardware and software engineers. The hardware paper has a section on aptitude, a section on digital design and a section on analogue design. We ask the students to select any one section between digital and analogue design. The software paper has an aptitude section and a software section. Candidates who fare well in the written test are shortlisted for interview. From my experience, the interviews are mostly based on problem-solving exercises and test the conceptual understanding rather than rote learning. We don’t pay too much importance to the B.Tech project done by the student,” says Ravikumar.
“For postgraduate students, our process is similar, except that we may go into their thesis. For candidates with a PhD, we also ask for a presentation where we invite our experts,” he adds.
One can understand this field from chip to ship level only by completing a successful project.
—Sasisekar K., President, RCS Online
The earlier, the better. If you ever tinkered with a broken radio set, you have already started. Academically, the right time to acquaint yourself with this niche field of electronics is when you are in the second or third year of engineering.
Dr Karthik points out, “An aspirant in this field is expected to know the physics of semiconductor devices, linear systems, probability and random variables, engineering mathematics (Fourier, Laplace and Z transforms), circuit analysis and engineering electromagnetics. For hiring a fresher, we look for in-depth understanding of second-and third-year engineering course curriculum rather than sector-
Solid Verilog/VHDL skills, familiarity with front-end design cycle, knowledge of synthesis and simulation tools, sound digital design fundamentals and knowledge of microprocessors would be an added advantage for any aspiring candidate.
What’s the right way to get started?
VLSI circuits are everywhere—your personal computer, your cellphone, your brand new state-of-the-art digital camera or for that matter any electronic gadget you dream to buy. Actually, this field involves packing more and more logic devices into progressively smaller areas. So the circuits that would have taken board-full of space can now be put into a small space few millimetres across!
According to Vivek Pawar, CEO, Sankalp Semiconductor, “The best way to start work on VLSI is to build core competency in this field. Component-level knowledge of electronic circuits and devices and thorough understanding of network theory, linear and digital design concepts are must-have.” Further, he emphasises on step-by-step knowledge acquisition of digital design, analogue design, board design and system design using different embedded tools.
To achieve this goal, Sankalp picks up second-and third-year electronics engineering students under its industry-academia ecosystem ‘Eklakshya’ and trains them following the ‘learning by doing’ principle.
According to Dr P.S. Bhat, director, Eklakhshya, “You may start with a typical analogue or digital design flow. For example, a digital design flow is specification→architecture→ RTL coding→RTL verification→synthesis→backend→tape out to foundry to get the end product.” Here the end product is a wafer with repeated number of identical ICs. All modern digital designs start with a designer writing a hardware description of the IC (using HDL) in Verilog/VHDL. A Verilog or VHDL program essentially describes the hardware (logic gates, flip-flops, counters, etc), the functionality and circuit block interconnects. Various electronic design automation (EDA) tools are available to synthesise a circuit based on the HDL. The most widely used synthesis tools come from Synposys and Cadence.
Without going into details, you may consider VHDL as ‘C’ language of the VLSI industry. VHDL stands for ‘VHSIC hardware definition language.’ This language is used to design the circuits at a high level, in two ways. It can either be a behavioural description of what the circuit is supposed to do or a structural description of what the circuit is made of. There are other languages too for describing circuits, such as Verilog, that work in a similar fashion. Both forms of description are then used to generate a very low-level description that actually spells out how all this is to be fabricated on the silicon chips.This results in the manufacturing of the intended IC.
Laying out the circuit components is a task common to all branches of electronics. The speciality in VLSI layout is the number of possible ways available to do this.
—Dr P.S. Bhat, Director, Eklakhshya
For an analogue design, the flow may vary to some extent: specifications → architecture→ circuit design→ simulation →layout→ parametric ex-traction/back annotation→final de-sign→tape out to foundry.
While digital design is highly automated now, very small portion of analogue design can be automated. For analogue, there is a hardware description language called AHDL, but it is not widely used as it does not accurately give the behavioural model of the circuit because of the complex analogue behaviour of the circuit. Many analogue chips are termed as ‘flat’ or non-hierarchical designs. This is true for small-transistor-count chips such as operational amplifiers, filters or power management chips. For more complex analogue chips such as data converters, the design is done at the transistor level, building up to the cell level, then the block level and finally integrated at the chip level. Not many EDA tools are available for analogue design even today and thus analogue design remains a difficult art. SPICE is the most useful simulation tool for analogue as well as digital design.
Keep in mind that digital VLSI circuits are predominantly CMOS-based. So the way normal blocks like latches and gates are implemented is different from what you have seen so far. However, the behaviour remains the same. All the miniaturisation involves new things to consider. A lot of thought has to go into the actual implementation as well as design.
Further, Dr Bhat points out, “Lay-ing out the circuit components is a task common to all branches of electronics. The speciality in VLSI layout is the number of possible ways available to do this; there can be multiple layers of different materials on the same silicon, different arrangements of smaller parts for the same component and so on. Each one has a separate layout.”
Layout is responsible for the functionality of the circuit. Power dissipation and speed in a circuit present a trade-off; if we try to optimise one, the other is affected. The choice between the two is determined by the way you choose to layout the circuit components. Layout can also affect the fabrication of VLSI chips, making it either easy or difficult to implement the components on the silicon.
How to tackle the reality?
Know where to apply your skillset. Analogue designs are mostly used for small-transistor-count precision circuits such as amplifiers, data converters, filters, phase-locked loops and sensors. In digital design, the progress in the fabrication of ICs has enabled designers to create fast and powerful circuits in smaller and smaller devices. This also means that you can pack a lot of functionality into the same area. The biggest application of this ability is in the design of ASICs. These ICs are created for specific purposes. The most common application area for an ASIC is DSP—signal filtering, image compression, etc. To understand better, consider the fact that a digital wristwatch normally consists of a single IC doing all the time-keeping as well as extra features like games, calendar, etc. SoCs (systems on a chip), on the other hand, are highly complex mixed-signal circuits (digital and analogue on the same chip). Network processor chips and wireless radio chips are examples of an SoC.
If it looks complicated to you, here’s an advice: “One can understand this field from chip to ship level only by completing a successful project,” says Sasisekar K., president, RCS Online. He advises to select designs that can address both the cost sensitivity and needs of the Indian market; for example, small chips for e-books or biosensors like blood-sugar monitoring devices. You should even try to get involved in stages like foundry-level fabrication and IP creation. In fact, these kinds of involvements can build a future generation of entrepreneurs in this field.
So don’t panic over the current job scenario; the time is perfect to resurrect your thought process on a very large scale. Devote your time to become an expert in VLSI. It will definitely bring ‘very large’ opportunities in the future.
The author is a consultant-editorial, industry & academia interface at EFY