Chapter 17

Basic analog IC design elements

As already stated, it is necessary for designers to know about the behavior and properties of components and basic circuits and about techniques and particular aspects of implementation. This is why, before going further these elements are grouped together in this part for those who might not be completely familiar with. Analog IC design is a branch of analog design. The difference comes from the integration that has many practical consequences. In turn, these particularities do not allow direct integration of a board schematic and then have an impact on the design:

  • The production cost of an IC is linked to the circuit area, not to the number of components. The larger the circuit, the higher the cost whatever the contents.
  • NRE costs for developing an IC are much higher than for developing a PCB. Delays between a design decision and feedback are much longer than for a breadboard.
  • Absolute values tolerances of components are poor, only matching can be reasonably good.
  • Passive components sizes are proportional to their value.
  • The cost of a 100 pF capacitor in an IC is about the same as 1500 gates in a 0.18 μ mCMOS process.
  • Changing a component value or a connection requires weeks to months and costs tens of thousand dollars.

17.1 Integrated components

Analog integrated circuits include both active devices and passive devices connected together in order to achieve their functionality. Integrated components as simple objects are defined by their material, shape and size.

  • Material: Mainly silicon, oxide and aluminum.
  • Shape: Depends on component type but most components are build from a number rectangles.
  • Size: Depends on component value or parameter.

The integrated components will be analyzed in terms of their characteristics and behavior, not in terms of technology except when a direct link exists between process and characteristics.

17.2 Devices

Integrated components belong to three families:

Availability of particular devices depends on process and options.

17.2.1 Active devices

These devices are bipolar transistors, MOS transistors and various diodes.

17.2.2 Passive devices

These devices are resistors, capacitors and inductors.

17.2.3 Parasitic devices

These devices include parasitic capacitors and resistors, isolation diodes, parasitic MOS, parasitic bipolar transistors and parasitic thyristors.