cascode amplifier

cascode amplifier

[′ka‚skōd ′am·plə‚fī·ər]
An amplifier consisting of a grounded-emitter input stage that drives a grounded-base output stage; advantages include high gain and low noise; widely used in television tuners.

Cascode amplifier

An amplifier stage consisting of a common-emitter transistor cascaded with a common-base transistor (see illustration). The common-emitter-common-base (CE-CB) transistor pair constitutes a multiple active device which essentially corresponds to a common-emitter stage with improved high-frequency performance. In monolithic integrated-circuit design the use of such active compound devices is much more economical than in discrete designs. A similar compound device is the common-collector-common-emitter connection (CC-CE), also known as the Darlington pair. See Integrated circuits

Cascade amplifierenlarge picture
Cascade amplifier

The cascode connection is especially useful in wideband amplifier design as well as the design of high-frequency tuned amplifier stages. The improvement in high-frequency performance is due to the impedance mismatch between the output of the common-emitter stage and the input of the common-base stage.

Another important characteristic of the cascode connection is the higher isolation between its input and output than for a single common-emitter stage, because the reverse transmission across the compound device stage is much smaller than for the common-emitter stage. In effect, the second (common-base) transistor acts as an impedance transformer. This isolation effect makes the cascode configuration particularly attractive for the design of high-frequency tuned amplifier stages where the parasitic cross-coupling between the input and the output circuits can make the amplifier alignment very difficult. See Amplifier, Transistor

References in periodicals archive ?
Among these products is a low noise RF cascode amplifier that is ideal for use in many RF functional blocks such as buffer amplifiers, low noise amplifiers, mixers, IF amplifiers, and voltage controlled oscillators in a wide variety of RF end-products.