cascode amplifier

cascode amplifier

[′ka‚skōd ′am·plə‚fī·ər]
(electronics)
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 ?
The replica folded cascode amplifier gives a low output offset voltage (lesser than 8 mV) up to 300 MHz, and the source-buffered folded cascode amplifier shows a low output offset voltage beyond 300 MHz's.
The proposed folded cascode amplifier uses transistor dimensions that are identical to the folded cascode amplifier, in order to make a fair comparison.
The basic circuit topology is a cascode amplifier with a large number of on-chip passive networks to satisfy the dual-band LNA specification.
In this topology, the Miller effect is more serious than in a cascode amplifier, since the first common source amplifier has a large voltage gain.
Some recent examples are the successful design and fabrication of a 5 to 100 GHz MMIC distributed amplifier with 5 dB gain,|4~ a 75 to 100 GHz MMIC cascode amplifier with 8 dB gain,|5~ and a 12 GHz MMIC low noise amplifier with 0.
Tan, "100 GHz High-Gain InP MMIC Cascode Amplifier," IEEE GaAs IC Symp.