Lim Hoi Yen - 36715

Microwave oscillators & low power amplifiers are made from:

Bipolar transistors Field-effect transistors (FETs) High electron mobility transistors (HEMTs) Varactor multipliers IMPATTS (IMPact ionization Avalanche Transit- Time diode) Transferred electron devices (Gunn devices)

Briefly explain each component

Lim Hoi Yen - 36715

Bipolar transistors

The transistor parameters α and β characterizes the current gain of the BJT. It is this gain that allow BJTs to be used as the building blocks of electronic amplifiers. The three main BJT amplifier topologies are common emitter, common base and common collector. It also can amplify analog or digital signals. It can also switch DC or function as an oscillator. Physically, a bipolar transistor amplifies current, but it can be connected in circuits designed to amplify voltage or power.

Field-effect transistors (FETs)

All FETs have source, drain, and gate terminals that correspond roughly to the emitter, collector, and base of BJTs. Most FETs have a fourth terminal called the body, base, bulk, or substrate.

High electron mobility transistors (HEMTs)

A high power pseudomorphic (PM) AlGaAs/InGaAs high electron mobility transistor (HEMT) with improved gain at 94 GHz. The transistor includes an InGaAs quantum well having a silicon planar doping layer located at the bottom. A donor layer comprises AlGaAs with a silicon planar doping layer. The resulting transistor exhibits superior gain and noise characteristics that relatively high power levels when operating at 94 GHz. The transistor is produced using an optimized growth process which involves growing the quantum well at a relatively low temperature and then raising the temperature to grow subsequent layers.

Varactor multipliers

Varactor multipliers use a variable-capacitance diode to generate harmonics of a lower frequency microwave signal. They are most useful for low harmonic conversion (multiplier factors of 2–4), while step-recovery diodes are able to generate more power at higher harmonics.

IMPATTS (IMPact ionization Avalanche Transit- Time diode)

IMPATTS use avalanche breakdown of a reverse-biased p-n junction to generate electrons and transmit time effects to have the electrons come out of the device exactly one half-cycle. The GaAs IMPATTS are fabricated utilizing low dislocation epitaxial grown doping structures and with high temperature metallization processes. They are also designed to have high output power when measured in a critically coupled cavity at the frequency of operation.

Transferred electron devices (Gunn devices)

Gunn devices use the properties of gallium arsenide to generate microwaves. They have three regions exist: two of those are heavily N-doped on each terminal, with a thin layer of lightly n-doped material between. In addition, they do not conduct in only one direction and cannot rectify alternating current like other diodes, which is why some sources do not use the term diode but prefer TED.