What is VLSI?

Very Large Scale Integration = analog and digital design for integrated circuits by combining transistors into analog or digital functionality. There are pure analog chips, pure digital chips and mixed-signal chips. First of all, analog design is mainly manual work and simulation. Digital on the other hand is via a high level description (HDL) and automated (regression) verification. Mixed signal is a combination of the two (for example in automotive a charge pump and oscillator is inside the chip (analog) and there is also a digital part (maybe a microcontroller and/or some control logic, calibration and/or status and/or control logic). For digital chips, a library is available based on the foundry tech and consists of gates, flops, glitch free clock gaters, memories. So, this is a chip (or IC).

What is an ASIC?

For specific applications, like a cable modem, a bitcoin miner, specific chips are designed, so called application specific IC or ASIC. They cost millions in development and are only cost effective in high volume. For lower volumes and prototyping, an FPGA is available, this is an ASIC but you can erase and reconfigure so you can map any design on it, or develop a design with many iterations. An FPGA is a field programmable gate array, but in fact an ASIC with an abstraction layer on top of it (cells, configurable routing, DSP blocks, blockrams). Smaller designs can be implemented on PLD’s. Next to ASIC, there is also ASSP, application specific standard product. An ASIC is devloped by a semiconductor company or by a subcontractor for that company. Hence the use if for one company. An ASSP, is targeted at more than one company. For example, in automotive a door lock module or a stepper motor driver with programmability can be used by more than one automotive module development company. Hence it is standard (multi customer) but also specific, like for headlamp/HVAC steppers.