Analog VLSI Vs Digital VLSI

VLSI is the current trend of manufacturing electronic integrated circuits. As we know that there are two divisions of electronic circuits(analog and digital) VLSI also have this division. In this article we will have a brief introduction about VLSI and then explain the differences between Analog VLSI and Digital VLSI in all aspects like design,testing,and application.

VLSI

An IC(Integrated Circuit) consisting of a large number of transistors, usually in the range of around 10 K to 1 Billion is called a VLSI circuit. The invention of Planar Technology for fabrication of transistors on a silicon wafer made VLSI circuits possible today. The fabrication techniques are improving every year minimizing process steps,leakage and shrinking transistor size even further. All these help in building power efficient,fast and reliable electronic circuits. Below shown is intel's core-i7 processor chip, it contains 700 Million transistors in just 1.5x1.5 square inches of silicon area.

Analog VLSI

Design aspects:

• It is comparatively difficult to design an analog VLSI circuit than a Digital VLSI circuit.
• Design of circuit is mostly manual.
• It cannot be described using a HDL(Hardware Descriptive Language).
• Analog modules are separated from the entire design because they need separate ground.
• Transistors are operated in linear and conduction regions.
• Transistors used are a bit larger than that used for digital circuits and run at a higher supply voltage.
• Design is not necessarily a CMOS design.

Testing aspects:

• It is difficult to test the circuit because in real system noise affects more and you cannot inject noise directly while testing the circuit.
• Phase delays also effect the circuit operation.

Application aspects:

• Only a small portion of an electronic circuit will be analog as their operation is highly affected by noise.
• These are mostly used for high speed amplifiers in communication.
• Used in ADCs(Analog to Digital Converters).
• Used at the modems,RF-receiver of mobile phones.

Digital VLSI

Design aspects:

• Mostly the design is automated and HDLs are used to describe the design.
• Transistors are much smaller and operate at lower supply levels than analog circuits.
• Transistors are operated in saturation(ON) and cutoff(OFF) regions.
• Regeneration of signal is easy so long wires is not a big problem for digital circuits.
• Design is mostly CMOS which have less power dissipation, high density, low cost and easily fabricated.

Testing aspects:

• Circuit can be tested exhaustively giving all possible inputs increasing reliability.
• Testing is easy and automated.
• Phase delays and noise do not affect the system operation.
• Failure conditions can be determined easily.
• The delays have to be analyzed correctly so that the setup and hold time violations do not happen.

Application aspects:

• Majority of the system is digital.
• Processors and microcontrollers are digital circuits.
• Used almost in all areas of application.

These are the major differences between Analog and Digital VLSI circuits.Did you find I missed any point? Please comment below and help me and my readers.