The main disadvantage of Mesfet structure is the presence of a Schottky metal gate. The Schottky metal gate limits the voltage on the gate to turn on the voltage of the Schottky diode. The turn on voltage is usually 0.7V for Schottky diodes. Therefore the threshold voltage must be lower than the turn on voltage (0.7V)
There are two main structures that are used for Mesfets;
There are two main structures, Non-Self aligned source and drain and Self aligned source and drain.
Below I have shown Non-Self aligned source and drain structure;
This is another form of Mesfet (Non-Self aligned source and drain). For this form the gate is placed on a section of the channel. The gate does not cover the whole length of the channel as the source and drain are formed before the gates.
Below I have shown a Self aligned source and drain structure;
This is another main form of Mesfet structure which is called the self aligned source and drain structure.
This form of structure mainly reduces the length of the channel and the gate covers the whole length. This occurs as in this structure the gate is formed before the source and drain.
The basic behaviour of the device
One typical application of the device
Mesfets are used in many RF amplifier applications. The semi conductor technology within the Mesfet provides for higher electron mobility, semi-insulating substrates are at lower levels of stray capacitance, because of the combination of both this means it can be an ideal RF amplifier. As a RF amplifier Mesfets can be used as microwave power amplifiers, high frequency low noise RF amplifiers oscillators and within mixers.
Mesfets have been designed to enable amplifiers using these devices that can operate up to 50 GHz – 100 GHz.
Ultra-wideband (UWB) radio is a technology that is being investigated for communications in our modern society
Ultra-wideband is radio technology is developed to transfer large amount of data wirelessly within small distances (1m to 30m), UWB operates by transmitting signals over a wide spectrum of frequencies.
Frequency bands and power levels used in UWB radio applications
Frequency bands used within UWB radio applications
UWB is a unique and new usage of a recently legalized frequency spectrum. UWB devices can use frequencies from 3.1GHz to 10.6GHz. Each bandwidth has approximately 500MHz mainly depending on its centre frequency.
For large bandwidth signals the FCC have put in place broadcast restrictions, because of these UWB devices can use very wide frequency bands while not emitting enough energy to be noticed by narrower band devices nearby. This allows large data to be transferred however it needs be within a small distance.
Power levels used with UWB radio applications
Give an example of an application of a UWB product, explaining briefly how it works, particularly saying why it would be a better solution than a wire-based communications system for that application
There are a large variety of UWB applications.
Examples include camcorders, digital cameras and portable mp3 players all with wireless connectivity.
UWB product Example; Alereon – Alereon is a company which produces products such as the one I have shown below.
Below I have shown an image of a product developed by Alereon; it is a laptop to wireless HDMI solution. It is a UWB product which pushes video
from your laptop using a USB stick to you Hi-def system.
This product will be able to sent and receive signals from 0m to 30m.
Why wireless?
- As this is wireless it would be much safer as there would not be any lose wiring hanging.
- The product can be used while moving around and moving to different rooms.
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Setting up this wireless product would much more efficient as no driver set ups would be needed.
Radio propagation issues that may affect short-range radio performance