Understanding VLSI Integrated Circuit design

In the world we live in, Electronic Gadgets have become an inseparable part of our lives. Add to this is the COVID pandemic, which has increased our dependence on gadgets to multifold. Electronics has also completely eliminated the Distance barrier throughout the World. Now, anyone can work for Any client from any part of the world.

Today, in this COVID era, We live in a World where physical meetings and discussions are avoided to the maximum extent. In these times of crisis, It is only due to the advancements in the field of Science and Technology that the World is going through a transition from  Physical to Online Meetings and discussions in a rather smooth way.

Needless to say, Advancements in the field of Electronics and Communication have been at the forefront of these transitions.

Role of Electronic Gadgets in our life

Electronic Gadgets like Mobile, Tablet, Laptops, and communication mediums like the Internet have become the most important weapons for this generation than ever.

A day or an hour, without a Mobile phone or internet is next to impossible to imagine for this generation.

Everything which comes into existence has primarily two parts to it. Front end and the Back end. When it comes to Gadgets and communication mediums like the Internet, we often tend to focus more on the Front end part of it like Interface, Apps, speed, and so on. We rarely think of what goes on at the Back end in order to provide such a smooth and reliable experience.

Today, the devices which we use in our daily life are very much faster, reliable, and cheaper than ever thought. This leads to a whole set of questions like:

How are these electronic devices designed to operate at such high speeds?
How are these devices becoming smaller and smaller?
How do these devices adapt to the ever-increasing demands of computation?
What does it take to design these Devices?
What is that one thing which is behind the designing and delivering of these incredibly efficient and high-speed devices?

In this post, Let’s answer some of these questions by having a look at one of the most important industries at the forefront of Technology revelations. Before we deep dive into the process of understanding What it takes to design, develop and bring highly efficient and intelligent gadgets into the market, let’s take a step back and think about what all questions arise when we see use Electronic gadgets from a functioning point of view.

Inside of an Electronic Gadget

Have you ever wondered how a small gadget like a Mobile phone has brought the whole world literally into our hands?

It’s not just into our hands but also into our pockets which we could have never imagined. It has also opened a plethora of opportunities to explore and understand almost everything we want. But how is this even possible?

What is inside the Mobile phone or be it any Electronic gadget that has this capability to perform the task assigned to it with extreme accuracy and reliability? let us have a look at what is inside of a Mobile phone.

As you can see from the above image, Every electronic gadget consists of a board on which all IC’s (Integrated Circuits) and other components like Resistor, capacitor, inductor, microphone are fabricated. Among all these components, the most important component is the Integrated Circuit.

The industry which specializes in the design, development, and manufacturing of these IC’s is VLSI (Very Large Scale Integration) Industry. The whole world is dependent on the VLSI industry and its IC’s to power and support all other industries.

In the next section, Let’s have a look at the history of the VLSI industry

History of VLSI

Very-large-scale integration (VLSI) is the process of creating an integrated circuit (IC) by combining millions of MOS transistors onto a single chip. VLSI began in the 1970s when MOS integrated circuit chips were widely adopted, enabling complex semiconductor and telecommunication technologies to be developed. The microprocessor and memory chips are VLSI devices.

Before the introduction of VLSI technology, most ICs had a very limited set of functions they could perform. An electronic circuit might consist of a CPU, ROM, RAM, Graphic cards, ALU, input and output ports, and so on. VLSI lets IC designers add all of these into one chip.

The history of the transistor dates to the 1920s when several inventors attempted devices that were intended to control current in solid-state diodes and convert them into triodes. Success came after World War II when the use of silicon and germanium crystals as radar detectors led to improvements in fabrication and theory. Scientists who had worked on radar returned to solid-state device development. With the invention of the first transistor at Bell Labs in 1947, the field of electronics shifted from vacuum tubes to solid-state devices.

With the small transistor at their hands, electrical engineers of the 1950s saw the possibilities of constructing far more advanced circuits. However, as the complexity of circuits grew, problems arose.[1] One problem was the size of the circuit. A complex circuit like a computer was dependent on speed. If the components were large, the wires interconnecting them must belong. The electric signals took time to go through the circuit, thus slowing the computer.

The advancements in the field of VLSI led to more powerful, portable, and smaller devices that are in use today.

Evolution of VLSI

The invention of the integrated circuit by Jack Kilby and Robert Noyce solved this problem by making all the components and the chip out of the same block (monolith) of semiconductor material. The circuits could be made smaller, and the manufacturing process could be automated. This led to the idea of integrating all components on a single-crystal silicon wafer, which led to small-scale integration (SSI) in the early 1960s, and then medium-scale integration (MSI) in the late 1960s.

The growth which the whole world is experiencing int the field of VLSI is dedicated to Gordon Moore, who is also called the father of VLSI.  He had formulated Moore’s Law in 1970 which is true even till today.

Moore’s law states that the Number of the Transistor of Transistors on a chip doubles every 18 months.

The prediction has become a target for miniaturization in the semiconductor industry and has had widespread impact in many areas of technological change.

Moore also co-founded a company NM Electronics which later became INTEL Corporation.

INTEL corporation gave rise to a Multi-million dollar industry which is Today referred to as VLSI Semiconductor Industry.

In the next section, let’s have a look at What is an ASIC and the process involved in Designing and Manufacturing an ASIC.

ASIC applications

Application-specific integrated circuit (ASIC ) is an IC targeted for a specific application, e.g., chips designed to run graphics on a game console, standard interfaces like USB, PCI bus to consumer electronics, special functions to control automotive electronics, and chips for smartphones.

In the early days of chip design, ASICs were a few thousand gates. With advancements in deep submicron technology, today’s ASICs run into millions of gates. Today, some of the more complex ASICs combine processors, memory blocks, and other ASIC or ASIC derivatives called IPs (intellectual property). These are called SoCs or System On Chip.

The reality is today’s SoCs will become the blocks or IPs for the future SoC design. This complex nature of ASIC development requires a well-structured design flow that is scalable and provides enough flexibility to designers and SoC integrators alike to define a methodology for a seamless design.

It is only because of the results of Advancements in SOC designing that today, we have the most powerful and efficient devices which are so small and portable that we can carry them anywhere and everywhere.

In the next section, let’s have a detailed look at the role of electronics and IC’s in different applications.

Smartphones

Today, A single Smartphone has replaced many things in our lives. Smartphones have replaced cameras, watches, alarm clocks, voice recorders, ipods, digital music players, calculators, maps, telephone directories, Television, scanners to name a few.

But the point to be noted is how is this possible?

This is only possible because of the different IC’s and the programs written for functioning of these IC’s based on the applications. Some of the applications for which IC’s are used in Smartphones are:

  1. Central Processing Unit (CPU): Samsung, Qualcomm IC’s
  2. RAM memory: Samsung IC’s
  3. Flash memory: Samsung, Toshiba IC’s
  4. 3G/4G modem: Qualcomm, Broadcomm IC’s
  5. Bluetooth: Murata IC’s
  6. Wifi: Broadcom IC’s
  7. NFC (Near Field Communication): Broadcom, NXP IC’s
  8. GPS: Broadcom, Qualcomm IC’s
  9. Accelerometer: STMicroelectronics IC’s
  10. Temperature Sensor IC’s
  11. Pressure Sensor IC’s
  12. Audio Codec IC’s: Qualcomm, Wolfson
  13. Voltage Regulator IC’s
  14. Power Management: Texas Instruments, Maxim Integrated IC’s.

Consumer Electronics

When we think of consumer electronics, devices which  mainly come to our mind are Television, Laptops, Desktops, Washing Machines, Tablets, POS machines, Wifi routers etc.

All these devices have Printed Circuit Boards (PCBs) which consist of a number of IC’s for various functionalities. For Television, IC’s are used for Power Supply Control, Picture Control, Connectivity, and so on. Similarly, for Laptops and Desktops, IC’s are used for Processing, Memory, Bluetooth, Wi-Fi and Ethernet Connectivity, Power control, camera, music, and so on.

Aviation Industry

Electronics play a very important role in the aviation industry. Its importance is such that there is a separate field dedicated to Aviation Electronics which is termed as Avionics.

Avionics are the electronic systems that are used in Aircraft, Artificial satellites, and spacecraft. Avionics systems include communications, navigation, the display and management of multiple systems, and hundreds of systems that are fitted to aircraft to perform individual functions. These can be as simple as a searchlight for a police helicopter or as complicated as the tactical system for an airborne early warning platform.

Electronic IC’s are used Communication systems to connect the flight deck to the ground and the flight deck to the passengers. On-board communications are provided by Public Address Systems (PAS) and Aircraft intercoms which also consist of multiple IC’s.

For a more detailed understanding of the Aviation Industry, I recommend you to visit the website http://aviationgeek.in/aviation-industry-in-india/

From the next section onwards, let’s deep dive into the designing part of Integrated Circuits.

ASIC Design Flow

A typical ASIC flow can be broadly categorized into logical design and physical design.

The above figure shows the detailed steps for ASIC design.

The logical design begins with high-level design specification and chip architecture. The chip architect captures high-level functional, power (how much power should the design consume), and timing (at what speed should the design operate) requirements.

This is followed by an RTL (Register Transfer-Level) description of the design. Commonly referred to as RTL (register transfer level), this provides an abstraction of the functional behavior of the circuit in terms of how the logical operations on signals enable data to flow between registers (flops) in a design. This is typically captured using hardware description languages (also referred to as HDL s) like Verilog, SystemVerilog, and VHDL.

Once the functionality of the design is coded, it is verified using simulation. Simulation is a process where various stimuli are applied to a representation of a design and the response of the design is captured. The objective is to validate that the resulting output matches
the desired functionality of the circuit. For example, if you implement an adder, which includes two inputs and one output, the test vector will emulate inputs as two numbers that need to be added, and output should represent the sum of these numbers.

At this stage, the design is ready for synthesis. Synthesis (or logic synthesis) is the step where RTL description is translated to a
the gate-level representation which is a hardware equivalent implementation of the functionality described in the HDL.

Synthesis tool will map this RTL description to a positive-edge-triggered flip flop with asynchronous reset. An HDL description is said to be synthesizable RTL if it can be consumed by industry-standard synthesis tools to map to a unique and unambiguous implementation. In this step, the designer also captures certain design and timing characteristics which are representative of the high-level objectives set
forth by the chip architect, like clock frequency, delays available in the block, and target library, so that the synthesis tool can optimize the design to meet the requirements.

After synthesis, the design is prepared for testability. DFT or design for testability is the technique to ensure that there are enough hooks in place to perform tests on the IC after manufacturing so that faulty parts don’t get shipped. One such technique is called scan insertion, also known as test-point insertion.

After synthesis and scan insertion, the hardware equivalent representation needs to be verified against the original RTL description so that the design intent is preserved. This is called equivalence checking and uses formal verification techniques.

At this stage, the design is also ready for STA or static timing analysis. It is worthwhile to note that equivalence checking only verifies the functionality of the implemented gate-level representation against the original description but not whether it meets the frequency target of the implementation, which is the responsibility of STA.

STA is a method of checking the ability of the design to meet the intended timing requirements, statically without the need for simulation. Most STA engines require the designers to specify timing constraints that model how the chip needs to be characterized at its periphery and what assumption to make inside the design so as to meet the timing requirements set forth by the chip architect.

STA step completes the logical design step and acts as the bridge between logical design and physical design.

Physical design begins with floor planning. After preliminary timing analysis, the logical blocks of the design are placed with the aim of optimizing area, aspect ratio, and how signals between the blocks interact. The objective is to ensure that there isn’t too much of inter-block interaction that causes congestion or difficulty in routing. These factors have a direct impact on power, area, timing, and performance.

Once the optimal floor plan is achieved, the connections between blocks are routed. During the synthesis stage, many assumptions are made about the clock network since that level of design information is not available until after the floorplan.

Floorplanning is followed by clock tree synthesis to distribute the clock as evenly as possible so as to reduce clock skew between different parts of the design. This step of floor planning, placement, and routing are called the layout of a design.

During the physical design, STA may be done multiple times to perform a more accurate timing analysis as the assumptions made during the initial implementation are gradually solidified.

Conclusion

VLSI is a very vast field. It is an ocean in itself. It is highly impossible to understand VLSI in a single post. I have tried my best to cover the overview of VLSI design. Hope you got a fair understanding of what VLSI actually is and what it takes to get into this Domain.

From my next post onwards, I will be deep-diving into VLSI Back end flow and it will be mainly dedicated to Physical Design.

Hope you liked this post. I request to provide comments to this post and subscribe to my newsletter for future posts on VLSI.

PS: This article is part of an assignment from Digital Deepak internship program. You can find out more about the Blog and his internship program  from the link  DigitalDeepak.com 

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