Limits
A pseudomorphic heterojunction bipolar transistor developed at the University of Illinois at Urbana-Champaign, built from indium phosphide and indium gallium arsenide and designed with compositionally graded collector, base and emitter, was demonstrated to cut off at a speed of 710 gigahertz.
Besides being record breakers in terms of speed, HBTs made of InP/InGaAs are ideal for monolithic optoelectronic integrated circuits. A PIN-type photo detector is formed by the base-collector-subcollector layers. The bandgap of InGaAs works well for detecting 1.55μm-wavelength infrared laser signals used in optical communication systems. Biasing the HBT to obtain an active device, a photo transistor with high internal gain is obtained. Among other HBT applications are mixed signal circuits such as analog-to-digital and digital-to-analog converters.
Read more about this topic: Heterojunction Bipolar Transistor
Famous quotes containing the word limits:
“The limits of my language mean the limits of my world.”
—Ludwig Wittgenstein (1889–1951)
“Whatever appeals to the imagination, by transcending the ordinary limits of human ability, wonderfully encourages and liberates us.”
—Ralph Waldo Emerson (1803–1882)
“Caring for children is a dance between setting appropriate limits as caretakers and avoiding unnecessary power struggles that result in unhappiness.”
—Charlotte Davis Kasl (20th century)