Q. Practical properties of operational amplifiers?

To achieve voltage gain and consequently power gain, the op amp must be biased by a dc source. The biasing network is comprised of the power supply and the passive circuit elements surrounding the device that provide the correct dc levels at the terminals. Terminals at which the dc bias is to be connected are provided on the op-amp package with the actual biasing networks connected internally. The manufacturer specifies the permissible range of supply-voltage values and the corresponding op-amp characteristics.

Manufacturers add prefixes to type numbers such as 741 to indicate their own codings, even though the specifications are similar. For example,

µA 741 Fairchild

LM 741 National Semiconductors

An extra letter is sometimes added to indicate a temperature specification. For example,

µA 741 A Military specification for guaranteed operation between -55 and +125°C

µA 741 C Commercial specification for temperature range of 0 to 70°C

Practical op amps are composed of several amplifier stages, a typical structure of which is shown in Figure. The three building blocks are the input differential amplifier, the common emitter stage, and the emitter follower output stage. Some of the op-amp practical properties follow.