User:Sepvh/Socsep

A System on a Chip is the commonly used term for an integrated circuit (IC) consisting of multiple - otherwise separated digital building blocks. These building blocks can have a variety of functions, typically including the everything a traditional microcontroller offers (central processing unit, program memory and programmable input/output) completed with an amount of on-chip system-level logic, not found on a microcontroller.

As System-on-Chip is a term that can entail many digital electronic designs, the line between a SoC and a microcontroller is rather subtle. Where the components of a microcontroller are - for the most part - similar between manufacturers, a System-on-Chip is an IC consisting of a microcontroller and some application specific system-level logic.

Examples include the PSOC (Programmable System on Chip) devices by Cyprus, which basically consist of a microcontroller and a small FPGA on the same chip, so consumers can add whatever peripherals within the available resources of the FPGA.

History
History of the sillicon market.

Changing landscape of SoC market

System-on-Chip in Systems Design
Contrary to what the name suggest, a System-on-Chip is usually part of a greater system. A cellphone for example is a system consisting of more than one chip, but instead consists of a printed circuit board (PCB) which in turn consists of several Systems-on-chip and their communication interfaces.

The most recent design philosophy in designing electronic systems is to break up the system and abide a divide and conquer strategy. This is in strong contrast to what system design used to be, where a single senior designer would understand every aspect of the chip.

In current projects, the system is divided in multiple layers. To illustrate this, we're using a cellphone as an example system, and break up the system as it was done when it was being designed. The layers are as follows:
 * System level. This is the cellphone in its entirety.
 * Printed Circuit Board. On this level all the electronics are wired together. The PCB has input/output with which the user communicates, as well as a small number of key chips - the System-on-Chip blocks - and their communication interfaces.
 * System-on-Chip. The SoC consists of a number of subsystems, each with their own application specific goal. The Video/Audio processor SoC for example has some processors and I/O (like a traditional microcontroller) as well as video- and audio-specific CODECs and RF interfaces.
 * Subsystems. Each subsystem consists of a number of designs, either original designs or intellectual property (IP) designs from other sources.

As we can see, the System-on-Chip design is one level of the system design hierarchy, consisting top-down of:
 * product design,
 * PCB design,
 * SoC design,
 * IP design.

Very-large-scale integration (VLSI)
...	ASIC

Fabrication
http://www.cl.cam.ac.uk/teaching/1011/SysOnChip/socdam-notes1011.pdf

Fabrication methods
SoC's can be fabricated using a variety of different technologies, each method having caracteristic strenghts and weaknesses.

Full Custom
In full custom design individual transistors and their interconnections are specified a layout. This method can offer maximal performance and minimal size if the layout is well designed, but difficult and extremely time-consuming to implement. It is a such best used when a high volume of highly optimised circuits is needed and impractical for larger SoC.

Standard cell


A standard cell represents an elemental logic funtions such as OR, AND, etc. but can also be a more complex structure like a flipflop. These cells are created using a full custom designed structure that provides the desired function. The benefit of using standard cell methodology is abstraction, when designing a system the psysical implementation does not need to be taken into account. The physical implementations of the cells are already optimised and are provided by a standard cell library. They usually have a fixed size in one dimension (often height) making them easy to line up in rows. The circuit is then made up of these rows off cells with power and grounds lines running inbetween. Standard cell methodology is often used for ASIC design.

SoC-class FPGA
Modern Field-programmable gate arrays (FPGA) have drasticly increased capabilities and often contain one or more processing units, these FPGA's can be classified as SoC's. They can be fully configured using a hardware description language (HDL) such as VHDL. making them excellent for prototyping a design or making SoC's with low development costs.

Authors
Written by Seppe Van Hees & Lars Peeters